JOURNAL OF ELECTRONIC MATERIALS
	ABSTRACTS Volume 24, Number 9, September 1995 This Month Featuring: Proceedings of the 1994 U.S. Workshop on the Physics and Chemistry of HgCdTe and Other IR Materials. View September 1995 Table of Contents.

SPECIAL ISSUE PAPERS

Subject areas discussed at the 1994 workshop include substrate technology, epitaxial material growth, surface and interface properties, defects, electrical and noncontact optical characterization. Forty-three of the 57 papers presented at the workshop appear in this publication. Much of the credit goes to the referees for their careful and prompt review of the manuscripts and to the authors for choosing this forum for presenting their results. The proceedings of the first ten workshops (from 1981-91) have been published in the Journal of Vacuum Science and Technology. Papers from the workshop from 1992 onwards appear in special issues of Journal of Electronic Materials.

Ishwara B. Bhat
Electrical, Computer & Systems Engineering Department
Rensselaer Polytechnic Institute
Troy, NY 12180-3590

Two-Dimensional Molecular Beam Epitaxy of {001} CdTe on Cd and Zn Terminated{001} GaAs
N.K. DHAR,¹ C.E.C. WOOD,² P.R. BOYD,³ H.K. POLLEHN,³ M. MARTINKA,⁴ J.D. BENSON,⁴ and J.H. DINAN⁴
1--Electrical Engineering Department, University of Maryland, College Park, MD 20742. Present address: Army Research Laboratory, Fort Belvoir, VA 22060. 2--Electrical Engineering Department, University of Maryland, College Park, MD 20742. 3--Army Research Laboratory, Fort Belvoir, VA 22060-5838. 4--Night Vision & Electronic Sensors Directorate, Fort Belvoir, VA 22060.

KEY WORDS CdTe/GaAs, growth modes, molecular beam epitaxy (MBE)

Amorphous layers of CdTe deposited on Cd or Zn terminated GaAs {001} surfaces can be recrystallized above ~200°C. Subsequent molecular beam epitaxy of CdTe proceeds in a two-dimensional mode and leads to layers which are specular and single domain {001}. Threading dislocation density in these layers was 1-2 x 10⁵ cm^-2. Values of full width at half maximum for x-ray rocking curves were as low as 80 arc-s.

Studies on the Growth of CdTe on Si Using Ge Interfacial Layer in an Organometallic Vapor Phase Epitaxial System
WEN-SHENG WANG and ISHWARA B. BHAT
Electrical, Computer and Systems Engineering Department, Rensselaer Polytechnic Institute, Troy, New York 12180.

KEY WORDS CdTe, organometallic vapor phase epitaxy (OMVPE), Ge interfacial layer

Epitaxial CdTe layers were grown using organometallic vapor phase epitaxy on Si substrates with a Ge buffer layer. Ge layer was grown in the same reactor using germane gas and the reaction of germane gas with the native Si surface is studied in detail at low temperature. It is shown that germane gas can be used to "clean" the Si surface oxide prior to CdTe growth by first reducing the thin native oxide that may be present on Si. When Ge layer was grown on Si using germane gas, an induction period was observed before the continuous layer of Ge growth starts. This induction period is a function of the thickness of the native oxide present on Si and possible reasons for this behavior are outlined. Secondary ion mass spectrometry (SIMS) data show negligible outdiffusion and cross contamination of Ge in CdTe.

Thermomigration of Tellurium Precipitates in CdZnTe Crystals Grown by Vertical Bridgman Method
T.S. LEE,¹ J.W. PARK,¹ Y.T. JEOUNG,¹ H.K. KIM,¹ C.H. CHUN, J.M. KIM,¹ I.H. PARK,² J.M. CHANG,² S.U. KIM,² and M.J. PARK²
1--Agency for Defense Development, Youseong P.O. Box 35, Taejeon, Korea. 2--Korea University, Anamdong 5-1, Seongbugku, Seoul, Korea.

KEY WORDS CdZnTe, effective diffusion coefficient, Te precipitates, thermomigration velocity, x-ray diffraction

Te precipitates in CdZnTe have been characterized by x-ray diffraction at room and higher temperatures. From the x-ray results at room temperature, it has been confirmed that Te precipitates in CdZnTe have the same structural phase as observed in elemental Te under high pressure. The x-ray results at higher temperature indicate that Te precipitates melt around 440°C. CdZnTe samples containing Te precipitates have been annealed at temperatures below and above 440°C with thermal gradient of ~70°C/cm. Results of the observation with infrared microscope before and after the annealings indicate distinct occurrence of thermomigration of Te precipitates in samples annealed at temperature above 440°C compared with ones annealed at temperature below 440°C. Thermo- migration velocity obtained from these results is ~50 µm/h. The average value for the effective diffusion coefficient of the metallic atoms in Te precipitates calculated by using the thermomigration velocity is ~3 x 10^-5 cm²/s.

Vertical Bridgman Techniques to Homogenize Zinc Composition of CdZnTe Substrates
T.S. LEE,¹ S.B. LEE,¹ J.M. KIM,¹ J.S. KIM,² S.H. SUH,² J.H. SONG,³ I.H. PARK,³ S.U. KIM,³ and M.J. PARK³
1--Agency for Defense Development, Youseong P.O. Box 35, Taejeon, Korea. 2--Korea Institute of Science and Technology, P.O. Box 131, Cheongryangri, Seoul, Korea. 3--Korea University, Anamdong 5-1, Seongbugku, Seoul, Korea.

KEY WORDS CdZnTe, modified Bridgman technique, numerical simulation, Zn homogeneity

In order to improve the Zn homogeneity along the axial direction of CdZnTe boule, we have employed a modified Bridgman technique using a (Cd, Zn) alloy source in communication with the melt, whose temperature has been gradually changed from 800 to 840°C during growth. Electron probe microanalysis (EPMA) measurements of Zn composition in the boule shows an excellent homogeneity of Zn along the axis of the CdZnTe boule compared with results in a boule grown by using a fixed source temperature. We have performed a numerical simulation to obtain the approximate temperatures of additional heating and cooling needed to improve the radial Zn homogeneity. CdZnTe boule has been grown by seeded vertical Bridgman furnace with two zones of heater and cooler. Ultraviolet/visible spectroscopic measurements of Zn composition over the length of the boule indicate that the radial distribution of Zn composition is very homogeneous in the body region of the boule, where the radial variation of Zn composition is ±0.0005.

Assessment of the Purity of Cadmium and Tellurium as Components of the CdTe-Based Substrates
R. TRIBOULET, A. AOUDIA, and A. LUSSON
CNRS, Laboratoire de Physique des Solides de Bellevue, 1, Place Aristide Briand, F 92195 MEUDON Cedex, France.

KEY WORDS Bridgman growth, CdTe, impurity incorporation

In order to assess the purity of their Cd and Te components, CdTe crystals have been grown by Bridgman using commercial batches of elements of purity ranging from 5N to 6N⁺. The assessment has been achieved through the classical optical and electrical techniques that solid state physics offers, on as-grown and annealed crystals. Some contamination by residual acceptors like Cu, Li, and P is shown to occur during the high temperature growth, mainly if uncoated silica tubes are used, as is emphasized within a comparison between the electrical and optical properties of crystals grown by melt-growth or at lower temperature by solution-growth.

Molecular Beam Epitaxial HgCdTe Material Characteristics and Device Performance: Reproducibility Status
J. BAJAJ, J.M. ARIAS, M. ZANDIAN, J.G. PASKO, L.J. KOZLOWSKI, R.E. DE WAMES, and W.E. TENNANT
Rockwell International Science Center, Thousand Oaks, CA 91360.

KEY WORDS Double layer heterostructures, focal plane array (FPA), HgCdTe, molecular beam epitaxy (MBE), p-n photodiodes

Extensive material, device, and focal plane array (FPA) reproducibility data are presented to demonstrate significant advances made in the molecular beam epitaxial (MBE) HgCdTe technology. Excellent control of the composition, growth rate, layer thickness, doping concentration, dislocation density, and transport characteristics has been demonstrated. A change in the bandgap is readily achieved by adjusting the beam fluxes, demonstrating the flexibility of MBE in responding to the needs of infrared detection applications in various spectral bands. High performance of photodiodes fabricated on MBE HgCdTe layers reflects on the overall quality of the grown material. The photodiodes were planar p-on-n junctions fabricated by As ion-implantation into indium doped, n-type, in situ grown double layer heterostructures. At 77K, diodes fabricated on MBE Hg_1-xCd_xTe with x 0.30 (_co 5.6 µm), x 0.26 (_co 7 µm), x 0.23 (_co 10 µm) show R₀A products in excess of 1 x 10⁶ ohm-cm², 7 x 10⁵ ohm-cm², and 3 x 10² ohm-cm², respectively. These devices also show high quantum efficiency. As a means to assess the uniformity of the MBE HgCdTe material, two-dimensional 64 x 64 and 128 x 128 mosaic detector arrays were hybridized to Si multiplexers. These focal plane arrays show an operability as high as 97% at 77K for the x 0.23 spectral band and 93% at 77K for the x 0.26 spectral band. The operability is limited partly by the density of void-type defects that are present in the MBE grown layers and are easily identified under an optical microscope.

Metalorganic Chemical Vapor Deposition of HgCdTe p/n Junctions Using Arsenic and Iodine Doping
P. MITRA,¹ T.R. SCHIMERT,¹ F.C. CASE,¹ S.L. BARNES,¹ M.B. REINE,² R. STARR,² M.H. WEILER,² and M. KESTIGIAN²
1--Loral Vought Systems Corporation, P.O. Box 650003, Dallas, TX 75265-0003. 2--Loral Infrared & Imaging Systems, Lexington, MA 02173-7393.

KEY WORDS Doping, heterojunctions, HgCdTe, metalorganic chemical vapor deposition (MOCVD)

We report new results on metalorganic chemical vapor deposition (MOCVD) in situ growth of long wavelength infrared (LWIR) P-on-n and medium wavelength infrared (MWIR) n-on-P HgCdTe heterojunction photodiodes using the interdiffused multilayer process (IMP). The n-type regions are doped with iodine using the precursor ethyl iodide (EI). I-doped HgCdTe using EI has mobilities higher than that obtained on undoped background annealed films and are comparable to LPE grown In-doped HgCdTe. The p-type layers are doped with arsenic from either tertiarybutylarsine (TBAs) or a new precursor, tris-dimethylaminoarsenic (DMAAs). The substrates used in this work are lattice matched CdZnTe oriented (211)B or (100)4°;<110>. Junction quality was assessed by fabricating and characterizing backside-illuminated arrays of variable-area circular mesa photodiodes. This paper presents four new results. First, carrier lifetimes measured at 80K on arsenic doped single HgCdTe layers are generally longer for films doped from the new precursor DMAAs than from TBAs. Second, we present data on the first P-on-n HgCdTe photodiodes grown in situ with DMAAs which have R₀A products limited by g-r current at 80K for _co = 7-12 µm, comparable to the best R₀A products we have achieved with TBAs. Third, we report the first experimental data on a new HgCdTe device architecture, the n-on-P heterojunction, with a wide gap p-type layer which allows radiation incident through the substrate to be absorbed in a narrower gap n-type layer, thereby eliminating interface recombination effects. With the n-on-P architecture, MWIR photodiodes were obtained reproducibly with classical spectral response shapes, high quantum efficiencies (70-75%) and R₀A products above 2 x 10⁵ ohm-cm² for _co = 5.0 µm at 80K. Fourth, we report 40K data for LWIR P-on-n HgCdTe heterojunction photodiodes (using TBAs), with R₀A values of 2 x 10⁴ ohm-cm² for _co = 11.7 µm and 5 x 10⁵ ohm-cm² for _co = 9.4 µm. These are the highest R₀A values reported to date for LWIR P-on-n heterojunctions grown in situ by MOCVD.

Real-Time Control of HgCdTe Growth by Organometallic Vapor Phase Epitaxy Using Spectroscopic Ellipsometry
SRIKANTESWARA DAKSHINA MURTHY, ISHWARA BHAT,¹ BLAINE JOHS,² SHAKIL PITTAL,² and PING HE²
1--ECSE Department, Rensselaer Polytechnic Institute, Troy NY 12180. 2--J.A. Woollam Co., 650 J Street, Suite 39, Lincoln, NE 68508.

KEY WORDS HgCdTe, in-situ monitoring, real-time control, spectroscopic ellipsometry

The use of spectroscopic ellipsometry for monitoring the vapor phase epitaxial growth of mercury cadmium telluride (Hg_1-xCd_xTe) in real-time is demonstrated. The ellipsometer is used to perform system identification of the chemical vapor deposition reactor used for the growth of CdTe and to measure the response of the reactor to different growth conditions. The dynamic behavior of the reactor is also studied by evaluating the gas transport delay. The optical constants of Hg_1-xCd_xTe are determined at the growth temperature for different compositions. In-situ real-time composition control is performed during the growth of Hg_1-xCd_xTe. The required target compositions are attained by the ellipsometer and appropriate corrections are also made by the controller when a noise input in the form of a temperature variation is introduced.

Low Temperature Growth of (100) HgCdTe Layers with DtBTe in Metalorganic Vapor Phase Epitaxy
K. YASUDA, H. HATANO, T. FERID, K. KAWAMOTO, T. MAEJIMA, and M. MINAMIDE
Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466, Japan.

KEY WORDS CdTe, growth characteristics, HgCdTe, HgTe, lattice strain, metalorganic vapor phase epitaxy (MOVPE)

Growth characteristics of (100) HgCdTe (MCT) layers by MOVPE at low temperature of 275°C were studied using ditertiarybutyltelluride as a tellurium precursor. Growths were conducted in a vertical narrow-spacing growth cell at atmospheric pressure. Cd composition of MCT layers were controlled from 0 to 0.98 using dimethylcadmium (DMCd) flow. The growth rate was constant for increase of DMCd flow. During the growth, Cd was incorporated preferentially into the MCT layers. Enhancement of Cd incorporation in the presence of Hg was also observed. Crystal quality and electrical properties were also evaluated, which showed that high quality MCT layers can be grown at 275°C. Strain in CdTe layers grown at 425 and 275°C was also evaluated. Lattice parameter of layers grown at 425°C approached bulk value at thickness of 5 µm, while layers grown at 275°C relaxed at 1 µm. The rapid strain relaxation of layers grown at 275°C was considered due to the layer growth on the strain relaxed buffer layer. The effect of the thermal stress on the relaxation of CdTe lattice strain was also discussed.

The Growth and Characterization of (211) and (133) Oriented (Hg,Cd)Te Epilayers (211)B GaAs by Organometallic Vapor Phase Epitaxy
G.J. GOUWS and R.J. MULLER
Mikomtek, CSIR, P.O. Box 395, Pretoria, South Africa.

KEY WORDS CdTe, HgCdTe, organometallic vapor phase epitaxy (OMVPE), orientation effects

The growth of CdTe buffer layers on (211)B GaAs substrates by organometallic vapor phase epitaxy (OMVPE) was studied, and it was found that, depending on the growth conditions, either the (211) or (133) epitaxial orientation could be formed. In some cases, an epilayer showing a mixed (211) and (133) orientation was also observed. The influence of several growth parameters on the orientation of the CdTe layer was investigated, and it was found that the Te/Cd ratio, together with the growth temperature, have the most significant effect in determining the epilayer orientation. From these results, it was then possible to select nominally optimized growth conditions for CdTe buffer layers of both orientations. (Hg,Cd)Te layers of the same orientations could then be grown and characterized. Although double crystal x-ray diffraction measurements indicated a somewhat better crystalline perfection in the (133) (Hg,Cd)Te layers, these layers showed a poor surface morphology compared to the (211) orientation. Measurement of etch pit densities also indicated defect densities to be typically half an order of magnitude higher in the (133) orientation. Diodes were formed by ion implantation in both orientations and significantly better results were obtained on the (211) (Hg,Cd)Te layers.

Improvement in HgCdTe Diode Characteristics by Low Temperature Post-Implantation Annealing
AKIRA AJISAWA and NAOKI ODA
Material Development Center, NEC Corporation, Kawasaki Kanagawa 216, Japan.

KEY WORDS HgCdTe, IR photodiodes, low temperature thermal annealing

Hg_1-xCd_xTe diodes (x~0.22) with different carrier concentrations in p type materials have been fabricated by employing an ion-implantation technique. The performances of the diodes, prior to and after low temperature post-implantation annealing, have been investigated in detail by model fitting, taking into account dark current mechanisms. Prior to the annealing process, dark currents for diodes with relatively low carrier concentrations are found to be limited by generation-recombination current and trap-assisted tunneling current, while dark currents for diodes with higher carrier concentrations are limited by band-to-band tunneling current. These dark currents in both diodes have been dramatically decreased by the low temperature annealing at 120~150°C. From the model fitting analyses, it turned out that trap density and the density of the surface recombination center in the vicinity of the pn junction were reduced by one order of magnitude for a diode with lower carrier concentration and that the carrier concentration profile in a pn junction changed for a diode with higher carrier concentration. The improvements are explained by changes in both carrier concentration profile and pn junction position determined by interaction of interstitial Hg with Hg vacancy in the vicinity of the junction during the annealing process.

Effect of Cooling Procedure After Annealing on Electrical Properties of Cd_0.2Hg_0.8Te Epitaxial Films Grown by Liquid Phase Epitaxy
Z. KAWAZU, S. OCHI, T. SONODA, and S. TAKAMIYA
Optoelectronic and Microwave Devices Laboratory, Mitsubishi Electric Corporation, 4-1, Mizuhara, Itami, Hyogo, 664 Japan.

KEY WORDS HgCdTe, Hg-rich annealing, Hg vacancies, thermal annealing

Effect of cooling procedure after annealing on the electrical properties of Cd_0.2Hg_0.8Te (CMT) epitaxial films grown by liquid phase epitaxy has been investigated to obtain the CMT films with low carrier concentration of 10¹⁴ cm^-3 reproducibly. Annealing has been performed at the temperature range from 260 to 350°C for 8 h in a fixed Hg vapor pressure. The quenching and the gradual cooling over a duration of 200 min after annealing have been employed for the cooling procedures. For quenched CMT samples, hole concentration decreases with decreasing anneal temperature and conduction type conversion from p to n is observed at 300°C. For the gradual cooling, all samples show n-type conduction for all annealing temperatures. Electrical properties of annealed layers strongly depend on the cooling procedure. The difference in electrical properties of the annealed CMT between two types of cooling procedure is mainly attributed to the difference in the annihilation of Hg vacancies during cooling procedure. The decrease of Hg vacancies during quenching is negligible, while Hg vacancies are annihilated during gradual cooling by rapid Hg diffusion. The diffusion coefficient of Hg is estimated more than 10^-9 cm²/s and this value is two orders of magnitude larger than that obtained by radiotracer technique.

Theoretical Evaluation of InTlP, InTlAs, and InTlSb As Long-Wave Infrared Detectors
A. SHER,¹ M. VAN SCHILFGAARDE,¹ S. KRISHNAMURTHY,¹ M.A. BERDING,¹ and A.-B. CHEN²
1--SRI International, Menlo Park, CA 94025. 2--Physics Department, Auburn University, AL 36849.

KEY WORDS HgCdTe, InTlP, InTlAs, InTlSb, IR detectors

We have evaluated three III-V semiconductor alloys--In_1-xTl_xP (ITP), In_1-xTl_xAs (ITA), and In_1-xTl_xSb (ITS)--as possible candidates for future long-wave infrared (LWIR) detector materials. The cohesive energies, elastic constants, band structures, electron mobilities, and phase diagrams are calculated and are compared to those of Hg_1-xCd_xTe (MCT) alloys. The band gaps of all three III-V alloys change from negative to positive values as the alloy composition x decreases from 1 to 0. The x values for the 0.1-eV gap are estimated to be 0.67, 0.15, and 0.08, respectively, for ITP, ITA, and ITS. While both ITP and ITA form stable zincblende solid solutions for all alloy compositions, zincblende ITS is stable only for a range of x less than 0.15. The complication of the phase diagram in ITS is caused by the existence of a stable CsCl phase for pure TlSb. The alloy mixing enthalpies for ITP and ITA are comparable to those in MCT, and their phase diagrams should be qualitatively similar, characterized by simple lens-shape liquidus and solidus curves. Both ITP and ITA have considerably larger cohesive energies and elastic constants than those of MCT, indicating that they are structurally robust. At a 0.1-eV gap, the band structures near the gap and the electron mobilities in ITP, ITA, and ITS are also found to be comparable to those of MCT. Since the lattice constants of TlP and TlAs are less than 2% larger than the respective values in InP and InAs, the latter should provide natural substrates for the growth of active LWIR alloys and offer a potential to integrate the detector array and read-out circuit.

Temperature Dependence of Band Gaps in HgCdTe and Other Semiconductors
SRINIVASAN KRISHNAMURTHY,¹ A. SHER,¹ M. VAN SCHILFGAARDE,¹ and A.-B. CHEN²
1--SRI International, Menlo Park, CA 94025. 2--Physics Department, Auburn University, Auburn, AL 36349.

KEY WORDS III-V semiconductors, band offset, electron-phonon interactions, HgCdTe and alloys, temperature-dependent band structures

Band-edge shifts induced by the electron-phonon interaction are calculated for HgCdTe alloys and various semiconductor compounds starting from accurate zero-temperature band structures. The calculated temperature variation of gaps agrees with experiments to better than 10% in all materials except InAs and InSb where the deviation is about 50%. While the simple picture that the intra (inter)-band transitions reduce (increase) the gap still holds, we show that both the conduction band edge E_c and valence band edge E_v move down in energy. These shifts in E_v affect the valence band offsets in heterojunctions at finite temperature. The temperature variations of valence band offset and the electron effective mass are also reported.

Defect Modeling Studies in HgCdTe and CdTe
M.A. BERDING, A. SHER, and M. VAN SCHILFGAARDE
SRI International, Menlo Park, CA 94025.

KEY WORDS CdTe, defect complexes, defects, HgCdTe

We have used a quasichemical formalism to calculate the native point defect densities in x = 0.22 Hg_1-xCd_xTe and CdTe. The linearized muffin-tin orbital method, based on the local density approximation and including gradient corrections, has been used to calculate the electronic contribution to the defect reaction free energies, and a valence force field model has been used to calculate the changes to the vibration free energy when a defect is created. We find the double acceptor mercury vacancy is the dominant defect, in agreement with previous interpretations of experiments. The tellurium antisite, which is a donor, is also found to be an important defect in this material. The mercury vacancy tellurium antisite pair is predicted to be well bound and is expected to be important for tellurium antisite diffusion. We consider the possibilities that the tellurium antisite is the residual donor and a Shockley-Read recombination center in HgCdTe and suggestions for further experimental work are made. We predict that the cadmium vacancy, a double acceptor, is the dominant defect for low cadmium pressures, while the cadmium interstitial, a double donor, dominates at high cadmium pressures.

Process Simulation for HgCdTe Infrared Focal Plane Array Flexible Manufacturing
C.R. HELMS,¹ J.L. MELéNDEZ,² H.G. ROBINSON,¹ S. HOLANDER,¹ J. HASAN,¹ and S. HALEPETE¹
1--Department of Electrical Engineering, Stanford University, Stanford, CA 94305. 2--Department of Electrical Engineering, Stanford University, Stanford, CA 94305. Current address: Texas Instruments, Inc., P.O. Box 655936, Dallas, TX 75265.

KEY WORDS Flexible manufacturing, HgCdTe, infrared focal plane arrays (IRFPAs), process simulations

The strategy and status of a process simulator for the flexible manufacture of HgCdTe infrared focal plane arrays is described. It has capabilities to simulate Hg vacancy and interstitial effects and cation impurity diffusion, for various boundary conditions in one dimension. Numerical complexity of these problems stems from the necessity of solving diffusion equations for each defect that are coupled to each other via nonlinear interaction terms. The simulator has already led to the prediction of heretofore unexplained experimental data. Current extensions of the one-dimensional simulator planned over the next few years include the addition of Te antisites, antisite-Hg vacancy pairs, and In-Hg vacancy pairs, ion implantation, and various energetic processes (such as ion milling). The sequential effect of various processes will be possible with the input to the simulator looking much like a process run sheet.

Effect of Dislocations on 1/f Noise of Long Wavelength Infrared Photodiodes Fabricated with HgCdTe Layers Grown on GaAs by Metalorganic Vapor Phase Epitaxy
S. MURAKAMI, H. NISHINO, H. EBE, and Y. NISHIJIMA
Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi, 243-01, Japan.

KEY WORDS 1/f noise, HgCdTe, IR photodiodes, metalorganic vapor phase epitaxy (MOVPE)

We studied the effect of dislocations on the 1/f noise current of long wavelength infrared photodiodes fabricated with HgCdTe layers grown on GaAs by metalorganic vapor phase epitaxy. N-on-p junctions were formed by boron ion implantation into Hg-vacancy doped epilayers. The 1/f noise dominated from 0.5 to 100 Hz, and shot noise caused by photocurrent dominated at higher frequencies. We observed two types of 1/f noise. One is caused by the leakage current generated at dislocations, and the other is induced by the photocurrent. The 1/f noise current increased with the photon flux in the low-etch pit density (EPD) range independently of EPD. It increased with EPD in the high-EPD range. The 1/f noise current measured at zero field of view increased with EPD. This suggests that the 1/f noise generated by the photocurrent dominated in the low-EPD range, and that the 1/f noise current caused by dislocations dominated in the high-EPD range. In order to obtain a thermal image of a room-temperature object, the 1/f noise current induced by background photon flux is as high as that caused by dislocations of more than 10⁷ cm^-2. Therefore, the 1/f noise current induced by the photocurrent is dominant in photodiodes fabricated with HgCdTe layers on GaAs, since the EPD is less than 2 x 10⁶ cm^-2. We expect the detectivity to be as high as with LPE-layers. We fabricated 64 x 64 photodiode arrays, and obtained a thermal image.

The Role of Surface Adsorbates in the Metalorganic Vapor Phase Epitaxial Growth of (Hg,Cd)Te onto (100) GaAs Substrates
J. GIESS,¹ J.E. HAILS,¹ A. GRAHAM,¹ G. BLACKMORE,¹ M.R. HOULTON,¹ J. NEWEY,¹ M.L. YOUNG,¹ M.G. ASTLES,¹ W. BELL,² and D.J. COLE-HAMILTON²
1--Defence Research Agency, St. Andrews Road, Malvern, Worcestershire, WR14 3PS, UK. 2--School of Chemistry, University of St. Andrews, St. Andrews, Fife, KY16 9ST, UK.

KEY WORDS HgCdTe, metalorganic vapor phase epitaxy (MOVPE), surface adsorption

It has been established that a compound present as an impurity in the propan-2-ol used in the preparation of GaAs (100) substrates for the metalorganic vapor phase epitaxy growth of (Hg,Cd)Te has a marked effect on the crystalline perfection and surface morphology of the resulting layers. In particular, the presence of this species, which contains Na, ensures that (i) the epitaxial overgrowth is of (100) orientation without the need for ZnTe nucleation layers, and (ii) the density of pyramidal hillocks on the surface can be reproducibly <10 cm^-2.

Reaction Chemistry and Resulting Surface Structure of HgCdTe Etched in CH₄/H₂ and H₂ ECR Plasmas
ROBERT C. KELLER, M. SEELMANN-EGGEBERT, and H.J. RICHTER
Fraunhofer Institut für Angewandte Festkörperphysik, 79108 Freiburg, Germany.

KEY WORDS Electron cyclotron resonance (ECR) plasma, ellipsometry, HgCdTe, plasma etching, x-ray photoelectron spectroscopy (XPS)

We report on several new aspects of etching of Hg_1-xCd_xTe (x = 0.22), HgTe, and CdTe in CH₄/H₂/Ar plasmas generated by an electron cyclotron resonance plasma source. Using a residual gas analyzer, we have identified elemental Hg, TeH₂, Te(CH₃)₂, and Cd(CH₃)₂ as the primary reaction products escaping from a HgCdTe surface during the plasma exposure. We have also demonstrated that a bias is not needed to etch HgCdTe at moderate temperatures (30-40^oC), as previously suggested by other researchers. We have also developed a technique that avoids the formation of hydrocarbon polymer films on a HgCdTe sample during etching. Moreover, we have examined by x-ray photoelectron spectroscopy analysis and ellipsometry the surface condition of HgCdTe resulting from etching with this technique at zero bias. After exposure to the CH₄/H₂/Ar plasma (or to a H₂/Ar plasma only), the HgCdTe samples exhibited a depletion of the HgTe component in the near surface region (increase of the x-value). The depletion covered a range from virtually x = 1 after H₂/Ar (10:2 in sccm) etching to values 0.4 < x < 0.5 after CH₄/H₂/Ar (7:7:2 in sccm) etching. Exposures to the plasmas were found to result in surface roughening of HgCdTe, however, plasmas rich in H₂ were observed to cause significantly rougher surfaces than plasmas with small H₂/CH₄ ratios. This difference in the resulting surface condition is attributed solely to chemical effects since the respective ion energies are considered to be below the damage threshold for HgCdTe in both cases. We also investigated the etching of HgTe and CdTe single crystals. The etch rate of HgTe was found to be over one order of magnitude higher than that of CdTe under similar conditions. This large difference in etch rates is assumed to be responsible for the observed preferential etching of the HgTe component indicated by the HgTe depletion of the HgCdTe surface region.

The Interface of Metalorganic Chemical Vapor Deposition-CdTe/HgCdTe
Y. NEMIROVSKY,¹ N. AMIR,¹ D. GOREN,¹ G. ASA,¹ N. MAINZER,² and E. WEISS²
1--Kidron Microelectronics Research Center, Department of Electrical Engineering, Technion, Haifa 32000, Israel. 2--SCD Semi-conductor Devices, Dept. 99, P.O. Box 2250, Haifa 31021 Israel.

KEY WORDS Band bending, CdTe, HgCdTe, metalorganic chemical vapor deposition (MOCVD), metal-insulator semiconductor (MIS) devices, surface passivation

The metalorganic chemical vapor deposition (MOCVD) growth of CdTe on bulk n-type HgCdTe is reported and the resulting interfaces are investigated. Metal-insulator-semiconductor test structures are processed and their electrical properties are measured by capacitance-voltage and current-voltage characteristics. The MOCVD CdTe which was developed in this study, exhibits excellent dielectric, insulating, and mechano-chemical properties as well as interface properties, as exhibited by MIS devices where the MOCVD CdTe is the single insulator. Interfaces characterized by slight accumulation and a small or negligible hysteresis, are demonstrated. The passivation properties of CdTe/HgCdTe heterostructures are predicted by modeling the band diagram of abrupt and graded P-CdTe/n-HgCdTe heterostructures. The analysis includes the effect of valence band offset and interface charges on the surface potentials at abrupt hetero-interface, for typical doping levels of the n-type layers and the MOCVD grown CdTe. In the case of graded heterojunctions, the effect of grading on the band diagram for various doping levels is studied, while taking into consideration a generally accepted valence band offset. The MOCVD CdTe with additional pre and post treatments and anneal form the basis of a photodiode with a new design. The new device architecture is based on a combination of a p-on-n homojunction in a single layer of n-type HgCdTe and the CdTe/HgCdTe heterostructure for passivation.

Electrical and Structural Properties of Epitaxial CdTe/HgCdTe Interfaces
V. ARIEL,¹ V. GARBER,¹ D. ROSENFELD,¹ G. BAHIR,¹ V. RICHTER,² N. MAINZER,³ and A. SHER⁴
1--Department of Electrical Engineering, Technion, Haifa 32000, Israel. 2--Solid State Institute, Technion, Haifa 32000, Israel. 3--SCD, P.O. Box 2250, Haifa 31021, Israel. 4--Soreq NRC, Yavne 70600, Israel.

KEY WORDS HgCdTe, metalorganic chemical vapor deposition (MOCVD), metal insulator semiconductor (MIS) devices, passivation

In this study, CdTe epilayers were grown by metalorganic chemical vapor deposition on epitaxial HgCdTe with the purpose of developing suitable passivation for HgCdTe photodiodes. Two types of CdTe layers were investigated. One was grown directly, in situ, immediately following the growth of HgCdTe. The second type of CdTe was grown indirectly, on top of previously grown epitaxial HgCdTe samples. In this case, the surface of the HgCdTe was exposed to ambient atmosphere, and a surface cleaning procedure was applied. The material and structural properties of the CdTe/HgCdTe interfaces were investigated using secondary ion mass spectroscopy, Auger electron spectroscopy, Rutherford back scattering, and x-ray double crystal diffractometry techniques. Electrical properties of the CdTe/HgCdTe heterostructure were determined by capacitance-voltage (C-V) characterization of Schottky barrier devices and metal insulator semiconductor devices. Also, a preliminary current-voltage characterization of n⁺ p photodiodes was performed. A theoretical model suitable for analysis of graded heterojunction devices was used for interpretation of C-V measurements.

Characterization of CdTe for HgCdTe Surface Passivation
L.O. BUBULAC,¹ W.E. TENNANT,¹ J. BAJAJ,¹ A.H.B. VANDERWYCK,¹ M. ZANDIAN,¹ W.V. MC LEVIGE,¹ J. SHENG,² and R. BRIGHAM²
1--Rockwell Science Center, Thousand Oaks, CA. 2--Charles Evans & Associates, Redwood City, CA.

KEY WORDS Atomic force microscopy, CdTe passivation, HgCdTe, molecular beam epitaxy (MBE), secondary ion mass spectrometry (SIMS)

The objectives of this work are to study the physical and chemical structure of CdTe films using secondary ion mass spectrometry (SIMS) and atomic force miroscopy (AFM) and to demonstrate the usefulness of these analytical techniques in determining the characteristics of CdTe-passivation films deposited by different techniques on HgCdTe material. Three key aspects of CdTe passivation of HgCdTe are addressed by different analytical tools: a) morphological microstructure of CdTe films examined by atomic force microscopy; b) compositional profile across the interface determined by Matrix (Te)--SIMS technique; c) concentration of various impurities across the CdTe/HgCdTe structure profiled by secondary ion-mass spectrometry.

Bake Stability of Long-Wavelength Infrared HgCdTe Photodiodes
A. MESTECHKIN, D.L. LEE, B.T. CUNNINGHAM, and B.D. MAC LEOD
Raytheon Company, Research Division, Lexington, MA 02173.

KEY WORDS HgCdTe photodiodes, long-wavelength infrared (LWIR) detectors, thermal annealing

The bake stability was examined for HgCdTe wafers and photodiodes with CdTe surface passivation deposited by thermal evaporation. Electrical and electro-optical measurements were performed on various long-wavelength infrared HgCdTe photodiodes prior to and after a ten-day vacuum bakeout at 80°C, similar to conditions used for preparation of tactical dewar assemblies. It was found that the bakeout process generated additional defects at the CdTe/HgCdTe interface and degraded photodiode parameters such as zero bias impedance, dark current, and photocurrent. Annealing at 220°C under a Hg vapor pressure following the CdTe deposition suppressed the interface defect generation process during bakeout and stabilized HgCdTe photodiode performance.

The Relationship Between Lattice Matching and Crosshatch in Liquid Phase Epitaxy HgCdTe on CdZnTe Substrates
S.P. TOBIN,¹ F.T.J. SMITH,¹ P.W. NORTON,¹ J. WU² M. DUDLEY,³ D. DI MARZIO,⁴ and L.G. CASAGRANDE⁴
1--Loral Infrared & Imaging Systems, Two Forbes Road, Lexington, MA 02173. 2--State University of New York at Stony Brook, Department of Materials Science and Engineering, Stony Brook, NY 11794. Current address: General Instruments Corp., Westbury, NY. 3--State University of New York at Stony Brook, Department of Materials Science and Engineering, Stony Brook, NY 11794. 4--Northrop-Grumman Advanced Development Center, Stewart Avenue, Bethpage, NY 11714.

KEY WORDS Lattice matching, mercury cadmium telluride, x-ray diffraction

X-ray topography provides a very sensitive map of lattice mismatch between a HgCdTe LPE epitaxial layer and its (111) CdZnTe substrate. A well-defined crosshatch pattern in the three <110> directions indicates a positive room-temperature lattice mismatch. For conditions of near-perfect lattice matching (±0.003% mismatch), the crosshatch pattern disappears, presumably because there are few or no misfit dislocations present near the interface, and a region free of topographic contrast is observed. The crosshatch-free region occurs for a small positive room-temperature mismatch (about 0.02%); this is attributed to differences in the lattice matching condition at room temperature and the growth temperature. For negative mismatches, where the film is in tension, a mosaic pattern, rather than a crystallographically oriented crosshatch, is observed in the topograph. Rocking curve full width at half maximum of the epitaxial layer is minimized in the crosshatch-free zone at a value nearly equal to that of the substrate. Etch pit density of the HgCdTe layer shows a strong minimum for perfect room temperature lattice matching, with values as low as 1 x 10⁴ cm^-2. For nearly lattice matched layers, crosshatch is present throughout the thickness of the epitaxial layer except for a narrow graded-composition region near the substrate interface. Crosshatch contrast appears to result from long-range strain fields associated with a misfit dislocation network near the substrate interface. Spatial variations in topographic features and mismatch across relatively small lateral distances are caused by variations in substrate alloy composition. For truly lattice-matched substrates, better control over the substrate lattice parameter is required.

Electron Cyclotron Resonance Plasma Etching of HgTe-CdTe Superlattices Grown by Photo-Assisted Molecular Beam Epitaxy
K.A. HARRIS,¹ D.W. ENDRES,² R.W. YANKA,² L.M. MOHNKERN,² A.R. REISINGER,² T.H. MYERS,³ A.N. KLYMACHYOV,⁴ C.M. VITRUS,⁴ and N.S. DALAL⁴
1--Martin Marietta Laboratories-Syracuse, P.O. Box 4840, Syracuse, NY 13221. Present address: II-VI Incorporated, 375 Saxonburg Boulevard, Saxonburg, PA 16056 2--Martin Marietta Laboratories-Syracuse, P.O. Box 4840, Syracuse, NY 13221. 3--Department of Physics, West Virginia University, Morgantown, WV 26506. 4--Department of Chemistry, West Virginia University, Morgantown, WV 26506.

KEY WORDS Electron cyclotron resonance (ECR), HgTe-CdTe superlattices, infrared

In order to form HgTe-CdTe superlattice diode arrays, a well-controlled etch process must be developed to form mesa structures on HgTe-CdTe superlattice layers. Wet etch processes result in nonuniform, isotropic etch profiles, making it difficult to control etch depth and diode size. In addition, surface films such as a Te-rich layer may result after wet etching, degrading diode performance. Recently, a dry etch process for HgTe-CdTe superlattice materials has been developed at Martin Marietta using an electron cyclotron resonance plasma reactor to form mesa diode structures. This process results in uniform, anisotropic etch characteristics, and therefore may be a better choice for etching superlattice materials than standard wet etch processes. In this paper, we will present a comparison of etch processes for HgTe-CdTe superlattice materials using electron microscopy, scanning tunneling microscopy, surface profilometry, and infrared photoluminescence spectroscopy to characterize both wet and dry etch processes.

Origin of Void Defects in Hg_1-xCd_xTe Grown by Molecular Beam Epitaxy
M. ZANDIAN, J.M. ARIAS, J. BAJAJ, J.G. PASKO, L.O. BUBULAC, and R.E. DEWAMES
Rockwell Science Center, Thousand Oaks, CA 91360.

KEY WORDS Atomic force microscopy, HgCdTe, molecular beam epitaxy (MBE), void defects

Characterization of defects in Hg_1-xCd_xTe compound semiconductor is essential to reduce intrinsic and the growth-induced extended defects which adversely affect the performance of devices fabricated in this material system. It is shown here that particulates at the substrate surface act as sites where void defects nucleate during Hg_1-xCd_xTe epitaxial growth by molecular beam epitaxy. In this study, we have investigated the effect of substrate surface preparation on formation of void defects and established a one-to-one correlation. A wafer cleaning procedure was developed to reduce the density of such defects to values below 200 cm^-2. Focal plane arrays fabricated on low void density materials grown using this new substrate etching and cleaning procedure were found to have pixel operability above 98.0%.

Analysis of Low Doping Limitation in Molecular Beam Epitaxially Grown HgCdTe(211)B Epitaxial Layers
P.S. WIJEWARNASURIYA,¹ M.D. LANGE,² S. SIVANANTHAN,¹ and J.P. FAURIE¹
1--University of Illinois at Chicago, Microphysics Laboratory, Physics Department, 845 W. Taylor St., Room 2236, Chicago, IL 60607-7059. 2--EPIR Ltd., P.O. Box 803827-P2E, Chicago, IL 60680-3827 and Physics Branch, Research and Technology Division, Naval Air Warfare Center Weapons Division, China Lake, CA 93555.

KEY WORDS HgCdTe, lifetimes, molecular beam epitaxy, n-type doping, transport properties

We report the results of the transport properties and the recombination mechanisms of indium-doped HgCdTe(211)B (x 23.0% ± 2.0%) layers grown by molecular beam epitaxy. We have investigated the origin(s) of the background doping limitation in these layers. Molecular beam epitaxially grown layers exhibit excellent Hall characteristics down to indium levels of 2 x 10¹⁵ cm^-3. Electron mobilities ranging from (2-3) x 10⁵ cm²/v-s at 23K were obtained. Measured lifetime data fits very well with the intrinsic band-to-band recombinations. However, below 2 x 10¹⁵ cm^-3 doping levels, mobility vs temperature curves starts to reflect nonuniformity in carrier distribution. Also, when we reduced the Hg vacancy concentration down to 10¹² cm^-3 range, by annealing at 150°C, Hall characteristics shows an increase in the nonuniformity in the epilayers. It was found that after annealed at 150°C, the obtained SR defect level has a different origin than the previously obtain Hg-vacancy related defect level.

Compositional Dependence of Cation Impurity Gettering in Hg_1-xCd_xTe
JOSé L. MELéNDEZ,¹ JOHN TREGILGAS,¹ JOHN DODGE,¹ and C.R. HELMS²
1--Corporate Research, Texas Instruments Inc., Dallas, TX 75265. 2--Department of Electrical Engineering, Stanford University, Stanford, CA 94305.

KEY WORDS Defect interactions, HgCdTe, impurity gettering, native point defects

Cation impurity gettering in Hg_1-xCd_xTe is described in the context of process models which include the interactions of the impurities and the dominant native point defects. Experimental results are presented using secondary ion mass spectroscopy (SIMS) profiles of Au redistribution in Hg_1-xCd_xTe (x = 0.2,0.3,0.4) following Hg anneals and ion mills, which are processes known to inject excess Hg interstitials. In either process, the IB impurity distributes preferentially to high vacancy regions. The junction depth of the low to high impurity transition is determined by SIMS. For Hg-rich anneals of Au-doped high vacancy concentration material, the impurity junction behavior with respect to anneal time and temperature is compared to that expected for type converted electrical junctions in vacancy-only material. For milled Au-doped Hg_0.7Cd_0.3Te with a high vacancy concentration, the impurity junction depths are approximately proportional to the amount of material removed, as was the case with x = 0.2 material. Hg anneal type-conversion rates are found to have a strong compositional dependence which compares favorably with the strong self-diffusion coefficient dependence on x-value. In contrast, the mill conversion rate has a weak x-value dependence. Effects of trace vs dominant Au levels compared to the background vacancy concentration are quantified. True decoration of intrinsic defect processes requires [Au]<<[Cation Vacancies].

A Comparison of the Diffusion of Iodine into CdTe, Hg_0.8Cd_0.2Te and Zn_0.05Cd_0.95Te
E.D. JONES,¹ J. MALZBENDER,¹ N. SHAW,² P. CAPPER,³ and J.B. MULLIN⁴
1--School of Natural and Environmental Sciences, Coventry University, Coventry, CV1 5FB, UK. 2--DRA Electronics Division, RSRE, St. Andrews Road, Great Malvern, Worcester, WR14 3PS, UK. 3--GEC Marconi Infra-Red, P.O.Box 217, Millbrook, Southhampton, S015 0EG, UK. 4--Electronic Materials Consultant, The Hoo, Brockhill Road, West Malvern, Worcester, WR14 4DL, UK.

KEY WORDS CdTe, HgCdTe, iodine diffusion, ZnCdTe

Studies on the diffusion of iodine into CdTe, mercury cadmium telluride (Hg_0.8Cd_0.2Te, referred to as MCT) and zinc cadmium telluride (Zn_0.05Cd_0.95Te, referred to as ZCT) in the temperature range of 20 to 600°C are compared and discussed. The concentration profiles were measured using a radiotracer sectioning technique. As with the diffusion studies using the halogens into CdTe, the profiles were composed of four parts to which a computer package consisting of the sum of four complementary error functions (erfc) gave satisfactory fits. The diffusivity for the diffusion of iodine into MCT was faster than for the diffusion into CdTe, which was faster than for the diffusion into ZCT. The high diffusivity for the fastest profile part at 20°C indicates that when iodine is diffused from the vapor into these materials, it is not a suitable long term stable dopant in devices where sharp junctions are required.

HgCdTe and Other Infrared Material Status in the Ukraine
V.K. MALYUTENKO
Institute of Semiconductor Physics, National Academy of Sciences, Kyiv, Ukraine.

KEY WORDS HgCdTe, infrared (IR) materials, thermoelectric coolers

This is the first article to explain and illustrate the HgCdTe and other infrared (IR) material status in the Ukraine. It develops the background needed to understand the what and where of IR physics, devices, and materials, but does not pretend to be a comprehensive treatment of the subject as some data still remain classified.

Numerical Simulation of HgCdTe Detector Characteristics
G.M. WILLIAMS and R.E. DE WAMES
Rockwell Science Center, 1049 Camino Dos Rios, Thousand Oaks, CA 91358.

KEY WORDS Heterojunctions, HgCdTe, infrared detectors

We discuss analytic and numerical models for HgCdTe photodiodes and present examples of their application. Analytic models can account for the performance obtained by many device architectures. Numerical and analytic models agree in predicting several aspects of device performance, such as diffusion limited dark current, confirming the approximations used in deriving the analytic models. Areas are noted where improvement in the numerical models would allow application to a wider range of device simulations. Useful results are obtained from the numerical simulators that cannot be obtained from our analytic model. Flux dependent R₀A products are shown to be a direct result of bias dependent quantum efficiency, a mechanism that is much more evident in heterojunction device architectures. Material compositional grading is demonstrated to lead to lower signal to noise ratio in devices designed to detect a particular infrared wavelength. We also show, particularly for high temperature operation, that heterojunction detectors can at best equal the performance of well-designed homojunction detectors; so, for photodetector design, heterojunctions do not offer any inherent performance advantages over homojunctions. Nevertheless, heterostructures, though ideally not required, may be helpful in achieving high performance in practice.

The Magnetic Field Dependence of R₀A Products in n-on-p Homojunctions and p-on-n Heterojunctions from Hg_0.78Cd_0.22Te Liquid Phase Epitaxy Films
M.C. CHEN, A. TURNER, L. COLOMBO, and D. CHANDRA
Texas Instruments Incorporated, Corporate Research and Development, Dallas, TX 75265.

KEY WORDS HgCdTe, IR detectors, magnetic field dependence, R0A products

The analysis of R₀A products as a function of magnetic field in n-on-p diodes using a simple diffusion current model has previously been shown to yield both J_ep/J_total ratio (the relative contribution of the p-side diffusion current) and µ_ep (the minority carrier, electron mobility). In this paper, we report the good agreement between the experimental and theoretical dependence of µ_ep on the hole concentration over a wide range between 1 x 10¹⁶ and 4 x 10¹⁷ cm^-3 in n-on-p homojunction diodes fabricated on undoped p-type Hg_0.78Cd_0.22Te liquid phase epitaxial (LPE) films. The averaged J_ep/J_total ratio varied between 68 and 90% with the hole concentration. These J_ep/J_total ratios indicate that other leakage current mechanisms than the p-side diffusion current were not negligible. Also, for the first time, comparative measurements were made on p⁺/n heterojunction diodes consisting of As-doped Hg_0.70Cd_0.30Te and In-doped Hg_0.78Cd_0.22Te LPE layers. Unlike a typical change in R₀A products by a factor of 2-3 in n-on-p homojunction diodes, the R₀A products in p⁺/n heterojunction diodes at 7 kG were typically only 2-3% higher than that at the zero field. The typical J_ep/J_total ratio in p⁺/n heterojunction diodes was about 3-4 %, which confirms the general belief that the p⁺ cap layer, due to the high doping and a larger bandgap, contributes very little to the total leakage current.

Magneto-Transport Characterization Using Quantitative Mobility-Spectrum Analysis
J. ANTOSZEWSKI,¹ D.J. SEYMOUR,¹ L. FARAONE,¹ J.R. MEYER,² and C.A. HOFFMAN²
1--Department of Electrical and Electronic Engineering, The University of Western Australia, Nedlands, WA 6009. 2--Code 5651, Naval Research Laboratory, Washington DC 20375.

KEY WORDS HgCdTe, Hall measurements, mobility spectrum analysis, transport properties

A quantitative mobility spectrum analysis (QMSA) of experimental Hall and resistivity data as a function of magnetic field is presented. This technique enables the conductivity contribution of bulk majority carriers to be separated from that of other species such as thermally generated minority carriers, electrons, and holes populating n and p doped regions, respectively, and two-dimensional species at surfaces and interface layers. Starting with a suitable first trial function such as the Beck and Anderson mobility spectrum analysis (MSA), a variation on the iterative procedure of Dziuba and Gorska is used to obtain a mobility spectrum which enables the various carrier species present in the sample to be identified. The QMSA algorithm combines the fully automated execution and visually meaningful output format of MSA with the quantitative accuracy of the conventional least-squares multi-carrier fitting procedure. Examples of applications to HgCdTe infrared detector materials and InAs/GaSb quantum wells are discussed. The ultimate goal of this paper is to provide an automated, universal algorithm which may be used routinely in the analysis and interpretation of magneto-transport data for diverse semiconductor materials and bandgap engineered structures.

Characterization of Molecular Beam Epitaxially Grown HgCdTe Epilayers by Mid-Infrared Interband Magneto-Absorption
P. HELGESEN, R. SIZMANN, T. SKAULI, T. COLIN, H. STEEN, and S. LøVOLD
1--Norwegian Defence Research Establishment, Division for Electronics, P.O. Box 25, N-2007 Kjeller, Norway.

KEY WORDS HgCdTe, interband magneto-absorption, molecular beam epitaxy (MBE), Moss-Burstein shift

Interband magneto-absorption is used to characterize molecular beam epitaxially (MBE) grown HgCdTe epilayers. Both the bandgap and the Moss-Burstein shift in n-doped layers are determined from the experiments. A heterostructure sample consisting of four layers with different compositions is also analyzed. Due to the good experimental sensitivity all four bandgaps are determined, in contrast to optical transmission analysis without a magnetic field where only the lowest gap is readily visible. The interband magneto-absorption signal strongly depends on the electron mobility. This has been used as an aid to optimizing the MBE growth conditions of HgCdTe layers on different substrate orientations.

Photoluminescence and Raman Studies of High Quality CdTe:I Epilayers
N.C. GILES¹ JAESUN LEE,¹ T.K. TRAN,² J.W. TOMM,³ and C.J. SUMMERS²
1--West Virginia University, Department of Physics, Morgantown, WV 26506-6315. 2--Quantum Microstructures Laboratory, Georgia Tech Research Institute, Atlanta, GA 30332-0800. 3--Quantum Microstructures Laboratory, Georgia Tech Research Institute, Atlanta, GA 30332-0800. Permanent Address: Humboldt-Universitat zu Berlin, Institut far Physik, Unter den Linden 6, D-10099 Berlin, Germany.

KEY WORDS CdTe, donors, photoluminescence (PL)

Low-temperature photoluminescence (PL) studies of iodine-doped CdTe epilayers have been performed. A compensating acceptor center which gives rise to deep-level PL emission at 1.491 eV is identified. From selective excitation PL studies, we assign this 1.491 eV line to the recombination of an associate donor-acceptor close pair, consisting of nearest neighbor substitutional sodium and iodine atoms (Na_Cd - I_Te). This neutral defect complex has a localized mode of 36.5 meV, which is much larger than the bulk CdTe lattice mode of 21.3 meV. The electronic energy level associated with this defect is 115 meV below the conduction band. Also, we use a combination of selective excitation PL and Raman spectroscopies to determine the ionization energy of the isolated shallow iodine donor (I_Te) in CdTe. We find that the donor binding energy of this anion-site hydrogenic donor is 15.0 (± 0.2) meV.

Status of Te-Rich and Hg-Rich Liquid Phase Epitaxial Technologies for the Growth of (Hg,Cd)Te Alloys
H.R. VYDYANATH
GenCorp Aerojet, 1100 W. Hollyvale Street, Azusa, CA 91702.

KEY WORDS HgCdTe, liquid phase epitaxy (LPE), Hg-rich and Te-rich LPE

In this review, we summarize the progress to-date in the technology of Hg_1-xCd_xTe liquid phase epitaxial growth from Hg-rich and Te-rich solutions. Areas of research which need to be pursued to further improve the state of the art in device performance are discussed.

Te-Rich Liquid Phase Epitaxial Growth of HgCdTe on Si-based Substrates
F.T. SMITH,¹ P.W. NORTON,¹ P. LO VECCHIO,¹ N. HARTLE,¹ M. WEILER,¹ N.H. KARAM,² S. SIVANANTHAN,³ and Y.P. CHEN³
1--Loral Infrared and Imaging Systems Inc., Two Forbes Rd, Lexington, MA 02173. 2--Spire Corporation, One Patriots Park, Bedford, MA 01730. 3--Microphysics Laboratory, Physics Department, University of Illinois at Chicago, P.O. Box 4348, Chicago, IL 60680.

KEY WORDS Heteroepitaxy, HgCdTe, liquid phase epitaxy (LPE)

The growth of high quality {111}B oriented HgCdTe layers on CdZnTe/GaAs/Si and CdTe/Si substrates by Te-rich slider liquid phase epitaxy (LPE) is reported. Although the {111} orientation is susceptible to twinning, a reproducible process yielding twin-free layers with excellent surface morphology has been developed. The electrical properties and dislocation density in films grown on these substrates are comparable to those measured in HgCdTe layers grown on bulk CdTe substrates using the same LPE process. This is surprising in view of the large lattice mismatch that exists in these systems. We will report details of both the substrate and HgCdTe growth processes that are important to obtaining these results.

Piezoelectric Effects in HgCdTe Devices
C.F. WAN, J.D. LUTTMER, R.S. LIST, and R.L. STRONG
Texas Instruments, Incorporated, Dallas, TX 75265.

KEY WORDS HgCdTe, piezoelectric effects, stress, strain

Piezoelectric effect in long-wavelength infrared (LWIR) HgCdTe has been studied using metal-insulator-semiconductor (MIS) and p-n homojunction devices. A cantilever beam technique was used to measure the shift in flatband voltage in the MIS devices as a function of applied strain, from which piezoelectric constant was derived. This is the first time such a value has been reported in the literature. Subsequent calculation showed that the thermal stress from cryogenic cool (from 300 to 77K) of hybridized infrared devices fabricated on (111) HgCdTe surfaces induced a piezoelectric field of ~1840 V/cm. This field is present in the space charge regions in the semiconductor where there is no free carrier. It reinforces the built-field in an n-on-p diode fabricated on the (111)A HgCdTe surface. Thus, the diode is more prone to the thermal stress than one fabricated on the (111)B surface. Electrical measurement of reverse-bias dark currents in HgCdTe photodiodes under applied compressive and tensile stress confirmed the existence of a strain-induced field in the junction.

1/f Noise and Material Defects in HgCdTe Diodes
R. SCHIEBEL, D. BARTHOLOMEW, M. BEVAN, R.S. LIST, and M. OHLSON
Central Research Laboratories, Texas Instruments Incorporated, MS 150, P.O. Box 655936, Dallas, TX 75265.

KEY WORDS 1/f noise, CdTe passivation, HgCdTe IR diodes

1/f noise is measured on long wavelength diodes as a function of device geometry, band gap, temperature, diode bias, and anneal temperature for a Te-rich CdTe passivation layer. The results show that for these diodes the 1/f noise is a bulk phenomena due to the modulation of generation recombination current associated with defects formed by the interdiffusion of Te-rich CdTe, and that these defects are located in the junction region. No 1/f noise is observed for the lowest interdiffusion anneal temperature.

Characterization of Liquid-Phase Epitaxially Grown HgCdTe Films by Magnetoresistance Measurements
J.S. KIM,¹ D.G. SEILER,¹ L. COLOMBO,² and M.C. CHEN²
1--Semiconductor Electronics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899. 2--Texas Instruments Incorporated, Dallas, TX 75265

KEY WORDS HgCdTe, liquid phase epitaxy, magnetoresistance

In this paper, we demonstrate that measurements of the magnetoresistance can be used as a valuable alternative to conventional characterization tools to study transport properties of advanced semiconducting materials, structures, or devices. We have measured magnetoresistance on two different systems, namely, three liquid-phase epitaxially grown HgCdTe films and two GaAs-based high-electron-mobility-transistor (HEMT) structures. The results are analyzed by using a two-carrier model as a reference in the context of the reduced-conductivity-tensor scheme. The HEMT data are in quantitative agreement with the two-carrier model, but the HgCdTe data exhibit appreciable deviations from the model. The observed deviations strongly indicate a mobility spread and material complexity in the HgCdTe samples which are probably associated with inhomogeneities and the resulting anomalous electrical behavior.

Nondestructive Characterization of Hg_1-xCd_xTe Layers with n-p Structures by Magneto-Thermoelectric Measurements
J. BAARS,¹ D. BRINK,¹ C.L. LITTLER,² and M. BRUDER³
1--Fraunhofer-Institut für Angewandte Festkörperphysik, Tullastrasse 72, D-79108 Freiburg i. Br., Germany. 2--Permanent address: Department of Physics, University of North Texas, Denton, TX 76203. 3--AEG-Aktiengesellschaft, INFRAROTMODULE, D-74072 Heilbronn, Germany.

KEY WORDS HgCdTe, magneto-resistance, thermoelectric properties

The thermoelectric properties of n-type Hg_0.79Cd_0.21Te (MCT) and of MCT layers with n-p structure have been investigated in transverse (B [invtee] --T) and longitudinal (B || --T) magnetic fields (0 B 16 kG) using the lateral gradient method at temperatures between 10 and 300K. The experimental results were analyzed by considering the contributions of electrons and holes to the magneto-thermoelectric effect and the scattering mechanisms involved. The analysis is based on a nonparabolic conduction band and Landau quantization as well as empirical relations for the band gap, the intrinsic carrier density, and the magnetoresistance. For n-type MCT at low temperatures (10 < T < 30K) and weak magnetic fields (B < 2 kG), the transverse magneto-thermoelectric effect (TME) was seen to be dominated by electron scattering on ionized defects. Longitudinal acoustic phonon drag was found to affect the TME in strong magnetic fields (B > 3 kG) at low temperatures (T < 20K). Longitudinal (LO) phonons were shown to prevail in the electron scattering at higher temperatures (T > 50K) in weak magnetic fields. With increasing magnetic fields, the effect of LO-phonon scattering decreases, and eventually the TME becomes independent of electron scattering. The longitudinal magneto-thermoelectric effect of n-type MCT was also found to exhibit magnetophonon oscillations due to LO-phonon scattering from both HgTe and CdTe phonons. The transverse magnetoresistance (TMR) of the n-type layers in the quantum region has been found to be linearly dependent on the magnetic field. Owing to the TMR of the n-type layers, the variation of the TME of p-n multiple layers with magnetic field is much larger than the variation of the Seebeck coefficient with temperature. Thus, the sensitivity to p-type layers is considerably enhanced compared to that of the Seebeck coefficient. As a result, the TME has proved to be particularly useful in determining the doping and composition of the constituent layers of MCT n-p structures.

Compositionally Graded HgCdTe Photodiodes: Prediction of Spectral Response From Transmission Spectrum and the Impact of Grading
D. ROSENFELD, V. GARBER, V. ARIEL, and G. BAHIR
Kidron Microelectronics Research Center, Department of Electrical Engineering, Technion - I.I.T., Haifa 32000, Israel.

KEY WORDS Compositional grading, HgCdTe, infrared (IR) transmission, photodiodes, spectral response

We have studied the infrared transmission spectrum and the optical performance of HgCdTe photodiodes containing a linear composition gradient in the active layer. Our objectives were to enable the prediction of the optical performance of a photodiode at 77K, based on the easily and nondestructively measured transmission spectra, as well as to gain a better understanding of the effects of the grading on the optical performance. Consequently, we address three issues here. We first establish improved characterization techniques that can provide accurate values of the necessary material parameters such as gradient in composition. Second, we present a model that can predict the optical response of a diode, based on the material properties and the diode's geometry. Third, we use the above-mentioned model for the theoretical calculations of the effects of the grading and the resulting built-in electric field on the diode's optical response.

Effect of a Valence-Band Barrier on the Quantum Efficiency and Background-Limited Dynamic Resistance of Compositionally Graded HgCdTe P-on-n Heterojunction Photodiodes
M.H. WEILER and M.B. REINE
Loral Infrared & Imaging Systems, Inc., Lexington, MA 02173.

KEY WORDS Band offset, heterojunctions, HgCdTe, quantum efficiency

A new analytical model for the bias-dependent quantum efficiency of a HgCdTe P-on-n heterojunction photodiode with a valence band barrier elucidates the important physics of the phenomenon and shows that the background-induced shunt resistance is a result of the same mechanism, that is, a tendency of the light-induced carriers to pile up in the base layer due to the retarding field produced by the barrier. A parameterized version of the model agrees well with experimental current-vs-voltage and noise measurements.