JOURNAL OF ELECTRONIC MATERIALS
	ABSTRACTS Volume 24, Number 11, November 1995 This Month Featuring: Proceedings of the 1995 Workshop on Organometallic Vapor Phase Epitaxy and Regular Issue Papers. View November 1995 Table of Contents.

SPECIAL ISSUE PAPERS

D. Kurt Gaskill and Stephen D. Hersee

Special Issue Guest Co-Editors

The Role of the Low Temperature Buffer Layer and Layer Thickness in the Optimization of OMVPE Growth of GaN on Sapphire
S.D. HERSEE,¹ J. RAMER,¹ K. ZHENG,¹ C. KRANENBERG,¹ K. MALLOY,¹ M. BANAS,¹ and M. GOORSKY²
1--Center for High Technology Materials, University of NewMexico, Albuquerque, NM 87131. 2--Department of Materials Science and Engineering, University of California, Los Angeles CA 90095-1595.

KEY WORDS GaN, metalorganic chemical vapor deposition (MOCVD), mobility

In agreement with previous work, a thin, low temperature GaN buffer layer, that is used to initiate OMVPE growth of GaN growth on sapphire, is shown to play a critical role in determining the surface morphology of the main GaN epilayer. X-ray analysis shows that the mosaicity of the main GaN epilayer continues to improve even after several mm of epitaxy. This continuing improvement in crystal perfection correlates with an improvement in Hall mobility for thicker samples. So far, we have obtained a maximum mobility of 600 cm²/V-s in a 6 µm GaN epilayer. Atomic force microscopy (AFM) analysis of the buffer layer and x-ray analysis of the main epilayer lead us to conclude that the both of these effects reflect the degree of coherence in the main GaN epitaxial layer. These results are consistent with the growth model presented by Hiramatsu et al., however, our AFM data indicates that for GaN buffer layers partial coherence can be achieved during the low temperature growth stage.

The Effect of Organometallic Vapor Phase Epitaxial Growth Conditions on Wurtzite GaN Electron Transport Properties
D.K. GASKILL, A.E. WICKENDEN, K. DOVERSPIKE, B. TADAYON, and L.B. ROWLAND
Laboratory for Advanced Material Synthesis, Naval Research Laboratory, Washington, DC 20375.

KEY WORDS GaN, mobility, organometallic vapor phase epitaxy (OMVPE)

The growth issues known to effect the quality of GaN organometallic vapor phase epitaxial films are reviewed and the best 300K mobility vs electron concentration data are discussed. The data probably represent transport properties intrinsic to films grown on sapphire. From the results of Hall measurements, the unintentional donor in high quality GaN films cannot be Si since the donor ionization energy is much larger than that of films intentionally doped with Si (36 vs 26 meV). Electrical properties of a doped channel layer are shown not to be significantly different from those of thick films which implies a viable technology for conducting channel devices. It is argued that 77K Hall measurements are a useful indicator of GaN film quality and a compilation of unintentionally and Si doped data is presented. The 77K data imply that, at least over a limited range, Si-doping does not appreciably change the compensation of the GaN. The 77K data indicate that the low mobilities of films grown at low temperatures are probably not related to dopant impurities.

Basic Studies of Gallium Nitride Growth on Sapphire by Metalorganic Chemical Vapor Deposition and Optical Properties of Deposited Layers
R. NIEBUHR, K. BACHEM, K. DOMBROWSKI, M. MAIER, W. PLETSCHEN, and U. KAUFMANN
Fraunhofer Institute for Applied Solid State Physics, Tullastr. 72, 79108 Freiburg, Federal Republic of Germany.

KEY WORDS Carbon, gallium nitride, growth rate, metalorganic chemical vapor deposition (MOCVD), photoluminescence, secondary ion mass spectrsocopy (SIMS)

We have studied the growth of gallium nitride on c-plane sapphire substrates. The layers were grown in a horizontal metalorganic chemical vapor deposition reactor at atmospheric pressure using trimethylgallium (TMG) and ammonia (NH3). Variation of the V/III ratio (150-2500) shows a distinct effect on the growth rate. With decreasing V/III ratio, we find an increasing growth rate. Variation of the growth temperature (700-1000°C) shows a weak increase in growth rate with temperature. Furthermore, we performed secondary ion mass spectroscopy measurements and find an increasing carbon incorporation in the GaN films with decreasing ammonia partial pressure and a growing accumulation of carbon at the substrate interface. Photoluminescence measurements show that samples with high carbon content show a strong yellow luminescence peaking at 2.2 eV and a near band gap emission at 3.31 eV. With increasing carbon content, the intensity of the 3.31 eV line increases suggesting that a carbon related center is involved.

On the Role of Interface Properties in the Degradation of Metalorganic Vapor Phase Epitaxially Grown Fe Profiles in InP
H. ROEHLE, H. SCHROETER-JANSSEN, P. HARDE, and D. FRANKE
Heinrich-Hertz-Institut für Nachrichtentechnik Berlin GmbH, Einsteinufer 37, D-10587 Berlin, Germany.

KEY WORDS InP, iron doping, metalorganic vapor phase epitaxy (MOVPE), substrate preparation

Fe doping profiles in InP layers grown by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE) were investigated by secondary ion mass spectroscopy. Different pre-treatments of the InP substrates proved to have substantially different effects on the Fe profiles which strongly indicate the relevance of underlying interfaces to dopant diffusion in subsequent layers, at least in the case of dopants occupying the group-III sublattice. We attribute the degradation of Fe profiles observed for some kinds of treatment to the emission of In interstitials from surfaces covered by oxides or other residues which are incompletely removed during the MOVPE preheat cycle. A favorable substrate preparation method for avoiding Fe profile degradation relies on etching by 5:1:1 H₂SO₄:H₂O₂:H₂O at room temperature followed by 30 min deionized water rinsing.

Controlled Oxygen Incorporation in Indium Gallium Arsenide and Indium Phosphide Grown by Metalorganic Vapor Phase Epitaxy
J.W. HUANG, J.M. RYAN, K.L. BRAY, and T.F. KUECH
Department of Chemical Engineering, University of Wisconsin, Madison, WI 53706.

KEY WORDS Deep levels, InxGa1-xAs, InP, metalorganic vapor phase epitaxy (MOVPE), oxygen

The defect engineering in metalorganic vapor phase epitaxy In_xGa_1-xAs and InP by controlled oxygen doping using diethyl aluminum ethoxide (DEALO) was developed in this study. DEALO doping has led to the incorporation of Al and O, and the compensation of shallow Si donors in In_xGa_1-xAs:Si with 0 ¾ x ¾ 0.25. With the same DEALO mole fraction during growth, the incorporation of Al and O was found to be independent of x, but the compensation of Si donors decreases with increasing In content. Deep level transient spectroscopy analysis on a series of In_xGa_1-xAs:Si:O samples with 0 ¾ x ¾ 0.18 revealed that oxygen incorporation led to a set of deep levels, similar to those found in DEALO doped GaAs. As the In composition was increased, one or more of these deep levels became resonant with the conduction band and led to a high electron concentration in oxygen doped In_0.53Ga_0.47As. Low temperature photoluminescence emission measurements at 12K on the same set of samples revealed the quenching of the near-band edge peak, and the appearance of new oxygen-induced emission features. DEALO doping in InP has also led to the incorporation of Al and O, and the compensation of Si donors due to oxygen-induced multiple deep levels.

Doping of Gallium Nitride Using Disilane
A.E. WICKENDEN,¹ L.B. ROWLAND,¹ K. DOVERSPIKE,¹ D.K. GASKILL,¹ J.A. FREITAS, Jr.,² D.S. SIMONS,³ and P.H. CHI³
1--Laboratory for Advanced Material Synthesis, Naval Research Laboratory, Code 6861, Washington, D.C. 20375-5347. 2--Sachs/Freeman Associates, Landover, MD 20785. 3--National Institute of Standards and Technology, Gaithersburg, MD 20899.

KEY WORDS Disilane, gallium nitride (GaN), metalorganic chemical vapor deposition (MOCVD), organometallic vapor phase epitaxy (OMVPE), silicon doping

The silicon doping of n-type GaN using disilane has been demonstrated for films grown on sapphire substrates by low pressure organometallic vapor phase epitaxy. The binding energy of an exciton bound to a neutral Si donor has been determined from low temperature (6K) photoluminescence spectra to be 8.6 meV. Nearly complete activation of the Si impurity atom in the GaN lattice has been observed.

A Novel Pseudomorphic (GaAs_1-xSb_x-In_yGa_1-yAs)/GaAs Bilayer-Quantum-Well Structure Lattice-Matched to GaAs for Long-Wavelength Optoelectronics
M. PETER, J. FORKER, K. WINKLER, K.H. BACHEM, and J. WAGNER
Fraunhofer-Institut für Angewandte Festkörperphysik, Tullastrasse 72, D-79108 Freiburg, Federal Republic of Germany.

KEY WORDS Band alignments, bilayer quantum well, critical layer thickness, GaAs1-xSbx/GaAs, quantum well, InyGa1-yAs/GaAs quantum well

Two types of quantum well (QW) structures grown lattice matched on (100) GaAs have been studied. The first type of structure consists of pseudomorphic GaAs_1-xSb_x/GaAs (x¾0.3) SQWs which show emission wavelengths longer than those reported for pseudomorphic In_yGa_1-yAs/GaAs QWs. However, the attractive emission wavelength of 1.3 µm has not been achieved. To reach this goal, a novel type of bilayer QW (BQW) has been grown consisting of a stack of two adjacent pseudomorphic layers of GaAs_1-xSb_x and In_yGa_1-yAs embedded between GaAs confinement layers. In this BQW, a type-II heterojunction is formed between GaAs_1-xSb_x and In_yGa_1-yAs, resulting in a spatially indirect radiative recombination of electrons and holes at emission wavelengths longer than those achieved in the GaAs_1-xSb_x/GaAs and In_yGa_1-yAs/GaAs SQWs. The longest 300K emission wavelength observed so far was 1.332 µm.

ZnMgSSe/ZnSSe/ZnSe-Heterostructures Grown by Metalorganic Vapor Phase Epitaxy
J. SÖLLNER,¹ J. SCHMORANZER,¹ H. HAMADEH,¹ B. BOLLIG,² E. KUBALEK,² and M. HEUKEN¹
1--Institut für Halbleitertechnik, RWTH Aachen, Templergraben 55, 52056 Aachen, Germany. 2--Werkstoffe der Elektrotechnik, Gerhard Mercator Universität, 47048 Duisburg, Germany.

KEY WORDS Heterostructures, metalorganic vapor phase epitaxy (MOVPE), scanning transmission electron microscopy (STEM), ZnSe, ZnSSe, ZnMgSSe

ZnMgSSe heterostructures have been grown in a low-pressure metalorganic vapor phase epitaxy system with the precursors dimethylzinc triethylamine, ditertiarybutylselenide, tertiarybutylthiol, and biscyclopentadienylmagnesium at 330°C and a total pressure of 400 hPa. The optimization of the single layers was carried out by means of low temperature photoluminescence. Only the near band edge emission was observable with negligible deep levels. The hetero-structures consisting of a triple ZnSe quantum well showed intense luminescence which hints at an effective carrier confinement. Scanning transmission electron microscopy investigations of the heterostructures still showed structural detects since the layers were not lattice matched to the GaAs substrate yet.

InSb, GaSb, and GalnSb Grown Using Trisdimethylaminoantimony
J. SHIN,¹ Y. HSU, T.C. HSU,¹ G.B. STRINGFELLOW,¹ and R.W. GEDRIDGE²
1--Department of Materials Science and Engineering, University of Utah, Salt Lake City, UT 84112. 2--Naval Air Warfare Center, China Lake, CA 93555.

KEY WORDS GaSb, InSb, organometallic vapor phase epitaxy (OMVPE), trisdimethylaminoantimony

GaInSb alloys as well as the constituent binaries InSb and GaSb have been grown by organometallic vapor phase epitaxy using the new antimony precursor trisdimethylaminoantimony (TDMASb) combined with conventional group III precursors trimethylindium (TMIn) and trimethylgallium (TMGa). InSb layers were grown at temperatures between 275 and 425°C. The low values of V/III ratio required to obtain good morphologies at the lowest temperatures indicate that the pyrolysis temperature is low for TDMASb. In fact, at the lowest temperatures, the InSb growth efficiency is higher than for other antimony precursors, indicating the TDMASb pyrolysis products assist with TMIn pyrolysis. A similar, but less pronounced trend is observed for GaSb growth at temperatures of less than 500°C. No excess carbon contamination is observed for either the InSb or GaSb layers. Ga_1-xIn_xSb layers with excellent morphologies with values of x between 0 and 0.5 were grown on GaSb substrates without the use of graded layers. The growth temperature was 525°C and the values of V/III ratio, optimized for each value of x, ranged between 1.25 and 1.38. Strong photoluminescence (PL) was observed for values of x of less than 0.3, with values of halfwidth ranging from 13 to 16 meV, somewhat smaller than previous reports for layers grown using conventional precursors without the use of graded layers at the interface. The PL intensity was observed to decrease significantly for higher values of x. The PL peak energies were found to track the band gap energy; thus, the luminescence is due to band edge processes. The layers were all p-type with carrier concentrations of approximately 10¹⁷ cm^-3. Transmission electron diffraction studies indicate that the Ga_0.5In_0.5Sb layers are ordered. Two variants of the Cu-Pt structure are observed with nearly the same diffracted intensities. This is the first report of ordering in GaInSb alloys.

Real-Time Optical Monitoring of Epitaxial Growth: Pulsed Chemical Beam Epitaxy of GaP and InP Homoepitaxy and Heteroepitaxy on Si
N. DIETZ, U. ROSSOW, D. ASPNES, and K.J. BACHMANN
Department of Materials Science and Engineering, Department of Physics, and Department of Chemical Engineering, North Carolina State University, Raleigh NC 27695-7919.

KEY WORDS GaP, InP, pulsed chemical beam epitaxy (PCBE), real-time monitoring

We present a study of the real-time monitoring of the homoepitaxial growth of GaP, InP, and the growth of InP/GaP and GaP/Si(001) heterostructures, combining single wavelength p-polarized reflectance (PRS), reflectance-difference spectroscopy (RDS), and laser light scattering (LLS) during pulsed chemical beam epitaxy with tertiarybutylphosphine, triethylgallium, and trimethylindium sources. The growth rate and the bulk optical properties are revealed by PRS with submonolayer resolution over 1000Å of film growth. The surface topography is monitored by LLS providing additional information on the evolution of the surface roughness as well as the nucleation/growth mechanism. The optical surface anisotropy, which is related to surface reconstruction and/or surface morphology, is monitored by RDS and compared with the results of PRS and LLS. The results are discussed with respect to the deposition kinetics, in particular as a function of the V:III flux ratio. The pulsed supply of chemical precursors causes a periodic alteration of the surface composition, which is observed as correlated periodic changes in the RD and PR signals, confirming the high sensitivity of both methods to surface chemistry.

Effect of Temperature on InGaAsP Alloy Composition
R.M. LUM,¹ M.L. MC DONALD,¹ E.M. MACK,¹ M.D. WILLIAMS,² F.G. STORZ,² and J. LEVKOFF³
1--AT&T Bell Laboratories, Murray Hill, NJ 07974. 2--AT&T Bell Laboratories, Holmdel, NJ 07733. 3--AT&T Microelectronics, Reading, PA 19612.

KEY WORDS InGaAsP, metalorganic vapor phase epitaxy (MOVPE), photoluminescence (PL)

The influence of growth temperature on the composition of InGaAsP films grown by low pressure metalorganic vapor phase epitaxy (MOVPE) is reported for quaternary (Q) alloys having bandgap wavelengths of _g=1.1, 1.3, and 1.5 µm. Films with these different Q-compositions were deposited lattice matched to InP at a growth temperature of 675°C. Subsequent growth experiments were then performed for each Q-composition in which the input gas flow rates were kept the same and only the temperature changed in 25°C decrements down to 600°C. Photoluminescence (PL) and lattice mismatch (LMM) measurements of the resulting films were used to determine the effect of growth temperature on film composition. The PL data indicate a temperature shift in the PL wavelength of -1.8 nm/°C for the 1.5Q composition, -2.9 nm/°C for 1.3Q, and -4.3 nm/°C for 1.1Q. Negative shifts were also observed in LMM of -80 ppm/°C for 1.5Q, -150 ppm/°C for 1.3Q, and -250 ppm/°C for 1.1Q. The Ga/In and P/As ratios of the Q-films were measured by secondary ion mass spectroscopy and correlated with full-wafer maps of the PL wavelength and lattice mismatch to gain insight into the processes responsible for wafer nonuniformity in MOVPE.

Characterization of Very High Purity InAs Grown Using Trimethylindium and Tertiarybutylarsine
S.P. WATKINS, C.A. TRAN, G. SOERENSEN, H.D. CHEUNG, R.A. ARES, Y. LACROIX, and M.L.W. THEWALT
Department of Physics, Simon Fraser University, Burnaby BC V5A 1 S6.

KEY WORDS InAs, metalorganic chemical vapor deposition (MOCVD), mobility

The growth of high purity InAs by metalorganic chemical vapor deposition is reported using tertiarybutylarsine and trimethylindium. Specular surfaces were obtained for bulk 5-10 µm thick InAs growth on GaAs substrates over a wide range of growth conditions by using a two-step growth method involving a low temperature nucleation layer of InAs. Structural characterization was performed using atomic force microscopy and x-ray diffractometry. The transport data are complicated by a competition between bulk conduction and conduction due to a surface accumulation layer with roughly 2-4 x 10¹² cm^-2 carriers. This is clearly demonstrated by the temperature dependent Hall data. Average Hall mobilities as high as 1.2 x 10⁵ cm²/Vs at 50K are observed in a 10 um sample grown at 540°C. Field-dependent Hall measurements indicate that the fitted bulk mobility is much higher for this sample, approximately 1.8 x 10⁵ cm²/Vs. Samples grown on InAs substrates were measured using high resolution Fourier transform photoluminescence spectroscopy and reveal new excitonic and impurity band emissions in InAs including acceptor bound exciton "two hole transitions." Two distinct shallow acceptor species of unknown chemical identity have been observed.

Step Structure During Organometallic Vapor Phase Epitaxial Growth of Ordered GaInP
G.B. STRINGFELLOW,¹ L.C. SU,¹ Y.E. STRAUSSER,² and J.T. THORNTON¹
1--Department of Materials Science and Engineering, University of Utah, Salt Lake City, UT 84112. 2--Digital Instruments Inc, Santa Barbara, CA 93103.

KEY WORDS Atomic force microscopy (AFM), GaInP, ordering, organometallic vapor phase epitaxy (OMVPE), surface steps

The nature of the steps on the nominally (001)-oriented surface of Ga_0.5In_0.5P lattice matched to GaAs has been studied using high resolution atomic force microscopy. The layers were grown by organometallic vapor phase epitaxy (OMVPE) at a temperature of 620°C on substrates misoriented by angles, _m, from 0 to 9° toward the [] direction in the lattice. An array of bunched steps from 25 to 50Å in height, depending on the substrate misorientation angle, is observed on the surface. An unusual feature of these bunched or super-steps, as compared to those seen for GaAs surfaces, is that they have relatively short lengths of a few thousand Ångstroms. In addition, not all of the steps congregate into the surface steps. Thus, the surface consists of three "phases": (001) flats, (11n) facets, and misoriented areas covered by an array of monolayer steps. The fraction of steps contained in the supersteps decreases monotonically as _m increases from 3 to 9°. Again, this differs from reports of the nature of GaAs surfaces grown under similar conditions where essentially all of the steps congregate into supersteps. The value of n for the (11n) facets also varies with misorientation angle: The angle between the (001) and the (11n) facets increases from approximately 11-12° for _m = 3° to nearly 30° for _m=9° An attempt was made to correlate the surface structure with ordering, which is observed to vary significantly with misorientation angle. The degree of order is found to increase monotonically with the fraction of steps forming supersteps.

Atomic Layer Epitaxy of InAs Using Tertiarybutylarsine
C.A. TRAN, R. ARES, S.P. WATKINS, G. SOERENSEN, and Y. LACROIX
Department of Physics, Simon Fraser University, Burnaby BC, V5A 1S6, Canada.

KEY WORDS Atomic layer epitaxy (ALE), InAs, tertiarybutylarsine

Tertiarybutylarsine and trimethylindium were used as precursors for atomic layer epitaxy of InAs. Self-limiting growth has been observed for a large temperature range between 350-410°C. In-situ reflectance difference spectroscopy was used to study the difference between the As and In self-limiting mechanisms on the InAs surface and also to optimize the growth parameters. Optical and transport properties of InAs grown epilayers show that high purity material can be achieved by atomic layer epitaxy.

Effects of Deposition Rate on the Size of Self-Assembled InP Islands Formed on GaInP/GaAs(100) Surfaces
C.M. REAVES,^1,2 V. BRESSLER-HILL,^1,3 W.H. WEINBERG,^1,3 and S.P. DENBAARS^1,2
1--Center for Quantized Electronic Structures, University of California, Santa Barbara, CA 93106. 2--Materials Department, University of California, Santa Barbara, CA 93106. 3--Chemical and Nuclear Engineering Department, University of California, Santa Barbara, CA 93106.

KEY WORDS Atomic force microscopy (AFM), InP/GaInP, quantum dots, self-assembled structures, Stranski-Krastanov growth

Utilizing the Stranski-Krastanov growth mode, three-dimensional InP islands are formed on a GaInP/GaAs surface using metalorganic chemical vapor deposition. The islands have been investigated with atomic force microscopy, and the effect of the deposition rate on the shape of the islands has been quantified. The height of the islands varies with deposition rate, whereas the base diameters are nearly constant around 1260 ± 35Å. The island height is 290 ± 12Å at a high (2.6 ML/s) deposition rate and decreases to approximately 250 ± 16Å for low (0.1 ML/s) and moderate (0.8 ML/s) deposition rates.

Growth of GaInP/GaAsP Short Period Superlattices by Flow Modulation Organometallic Vapor Phase Epitaxy
K.L. WHITTINGHAM,¹ D.T. EMERSON,¹ J.R. SHEALY,¹ M.J. MATRAGRANO,² and D.G. AST²
1--OMVPE Facility, School of Electrical Engineering, Cornell University, Ithaca, NY 14853. 2--School of Materials Sciences and Engineering, Cornell University, Ithaca, NY 14853.

KEY WORDS GaInP/GaAsP, organometallic vapor phase epitaxy (OMVPE), short period superlattice

One disadvantage of the GaInP/GaAs system is the difficulty often encountered in synthesizing the quaternary material GaInAsP, required to span the intermediate bandgap range (1.42-1.91 eV). Recent studies report on an extensive miscibility gap in this alloy. In this study, we investigate an alternative approach to the growth of material within this bandgap range. We have grown by flow-modulation organometallic vapor phase epitaxy, GaInP/GaAsP superlattices with periods ranging from 80 to 21Å. These are the first reported short-period superlattices in this material system. Effects of superlattice (SL) period, growth temperature, and phosphorous composition in the wells were studied by photoluminescence, high resolution x-ray diffraction, atomic force microscopy, and transmission electron microscopy. The effect of growth temperature on the structural quality of the SLs is correlated to ordering effects in the GaInP layers. Variations in the P composition and the SL period result in a shift in the room temperature bandgap emission from 1.51 to 1.74 eV. Strain-compensated structures have been realized by growing the SL barriers in compression.

The Properties of MOVPE Grown 1.3 µm DFB MQW Lasers Infilled With Semi-Insulating InP Fabricated On Semi-Insulating Substrates
N. CARR,^1,2 J. THOMPSON,¹ G.G. JONES,¹ I. GRIFFITH,¹ A.J. MOSELEY,¹ and P.M. CHARLES¹
1--GEC-Marconi Materials Technology, Caswell, Towcester, Northants. NN12 8EQ, England. 2--Current address: Hewlett-Packard, Whotehouse Road, Ipswich IP1 5PB, Suffold, England.

KEY WORDS Distributed feedback (DFB), GaInAsP, metalorganic vapor phase epitaxy (MOVPE), MQW laser

The use of optoelectronic integrated circuits (OEICs) is now emerging as a practical technology for a variety of applications, particularly in advanced telecommunications. OEICs consist of a range of devices such as lasers, waveguides, modulators, amplifiers, transistors, detectors, etc. fabricated on the same substrate. When a semi-insulating substrate is used, these devices can be electrically isolated by channel etching, resulting in a low capacitance structure with reduced electrical interference between the subcomponents. One of the devices which is particularly advantageous for this type of integration scheme is the distributed feedback (DFB) laser. The laser can be made to function more efficiently by minimizing the current flowing outside the active region. This can be achieved by surrounding the active region with semi-insulating iron doped InP. This work describes for the first time, the MOVPE growth, fabrication, and device characterization of 1.3µm buried heterostructure DFB MQW lasers, which combine the advantages of using both a semi-insulating substrate and a semi-insulating infill region in the same device structure. The potential advantage of this design scheme is improved OEIC performance as a result of, reduced capacitance and electrical crosstalk, enhanced laser output power, higher speed, increased efficiency, wider operating temperature and reduced threshold current. The laser active region consists of 8 x 140Å quantum wells of GaInAsP (=1.3µm) and 110Å barriers of GaInAsP (=1.07 µm). Single mode 1.3µm devices of length 250µm operating at room temperature produced threshold currents of 8 mA, efficiencies of up to 25%, output powers of 18 mW at 80 mA (pulsed), and a frequency response greater than 12GHz. The parasitic capacitance was estimated to be less than 3 pF.

Semi-Insulating Selective Regrowth of Surface Light Emitting Diodes
CHING-LONG JIANG, MARK MASHAS, MARIA FERREIRA, JOHN KULICK, EUGENE IMHOFF, and WILLIAM REYSEN
AMP Incorporated, Lytel Division, Somerville, NJ 08876.

KEY WORDS Analog, circular mesa, high speed, light emitting diode (LED), organometallic vapor phase epitaxy (OMVPE), patterned substrate, selective growth, semi-insulating

Selective regrowth of indium phosphide (InP) using organometallic vapor phase epitaxy (OMVPE) on a circular shaped mesa has been demonstrated for the first time. Inclusion of an interfacial layer of indium gallium arsenide phosphide between the circular dielectric mask and the underlying material produces a favorable smooth mesa profile by controlling the level of undercut during mesa etching. This combination of profile and undercut was found to be critical for successful selective regrowth and planarization. To the best of our knowledge, this is the first time that a surface light emitting diode has been demonstrated with a selective OMVPE semi-insulating regrowth. The semi-insulating InP layer reduces parasitic capacitance and improves the heat dissipation out of the device. These salient features make these devices suitable for high speed digital and analog communication applications.

Maskless Selective Area Growth of InP on Sub-um V-Groove Patterned Si(001)
R.F. SCHNABEL,¹ A. KROST,¹ M. GRUNDMANN,¹ D. BIMBERG,¹ and H. CERVA²
1--Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstr. 36, D-10623 Berlin, Germany. 2--Siemens AG, Otto-Hahn-Ring 6, D-81739 München, Germany.

KEY WORDS InP, metalorganic chemical vapor deposition (MOCVD), patterned Si substrate

Low pressure metalorganic chemical vapor deposition of InP on exactly oriented Si(001) substrates with a periodic V-groove pattern of periodicity ¾1.2 µm using a two temperature growth sequence (400 and 640°C) is reported. Planar InP layers with extremely low defect density of 7 x 10⁴ cm^-2 are obtained. For InP on V-grooves of width g ¾1.0 µm, a planar surface is formed after less than 1 µm of growth. Formation or suppression of antiphase domains (APDs) is a function of the width s of the (001)-oriented ridges. For s ¾1 µm, epilayers are single domain and the [] direction is oriented parallel to the grooves. At 400°C, nucleation starts homogeneously on {111}-sidewalls and (001)-facets. While heating up to 640°C, InP migrates into the grooves, depleting almost completely the (001)-facets. During growth of the main layer, first the V-grooves are filled up. Subsequently (001)-ridges are overgrown laterally or voids are formed on top of them. This mechanism is responsible for both planarization and APD-suppression. The surface migration length of InP on Si(001) at 640°C is estimated to be ~0.5 µm.

Growth, Characterization, and Modeling of Ternary InGaAs-GaAs Quantum Wells by Selective-Area Metalorganic Chemical Vapor Deposition
A.M. JONES,¹ M.L. OSOWSKI,¹ R.M. LAMMERT,¹ J.A. DANTZIG,² and J.J. COLEMAN¹
1--Microelectronics Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801. 2--Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801.

KEY WORDS InGaAs, metalorganic chemical vapor deposition (MOCVD), quantum wells

A computational diffusion model is used to predict thickness and composition profiles of ternary In_xGa_1-xAs quantum wells grown by selective-area, atmospheric pressure metalorganic chemical vapor deposition (MOCVD), and its accuracy is investigated. The model utilizes diffusion equations and boundary conditions derived from basic MOCVD theory, with reaction parameters derived from experimental results, to predict the concentration of each column III constituent throughout the concentration boundary layer. Solutions to these equations are found using the two-dimensional, finite element method. The growth thickness profiles of GaAs, InP, and In_xGa_1-xAs deposited by selective-area MOCVD are observed by conventional profilometry, and compositions are measured indirectly by laser emission wavelengths. The data presented show that the model accurately predicts growth thickness and composition profiles of ternary III-V materials grown by selective-area MOCVD.

Investigation of the Wafer Temperature Uniformity in an OMVPE Vertical Rotating Disk Reactor
A.I. GURARY, A.G. THOMPSON, R.A. STALL, W.J. KROLL, and N.E. SCHUMAKER
EMCORE Corporation, 35 Elizabeth Avenue, Somerset NJ 08873.

KEY WORDS Rotating disk reactor, rotating wafer thermal imaging, vapor phase epitaxy, wafer temperature uniformity

Measuring the wafer temperature uniformity is one of most difficult problems in the development of organometallic vapor phase epitaxy (OMVPE) equipment. Until recently, the lack of a good experimental technique limited the understanding of OMVPE rotating disk reactor (RDR) thermal dynamic. We have developed a rotating wafer thermal imaging technique, which for the first time allows a real-time experimental investigation of the temperature distribution across the wafer in an RDR under realistic deposition conditions. This technique allows investigation on how process parameters such as the growth temperature (from 650 to 800°C), reactor pressure (from 10 to 620 Torr), reactant flow (from 2 to 30 slm), and wafer carrier rotation speed (from 300 to 1030 rpm) affect the wafer temperature uniformity. This information has allowed us to establish under which conditions single or multi-zone heating should be used in the OMVPE reactor. A wafer temperature uniformity of better than 1°C was demonstrated for both an optimized single zone heating system under a selected combination of process parameters, and for a two-zone heating system over a wide range of the process parameters.

Comparison of OMVPE Grown GaAs/AlGaAs and GaAs/InGaP HEMT and PHEMT Structures
K.A. JONES,¹ R.T. LAREAU,¹ T. MONAHAN,¹ J.R. FLEMISH,¹ R.L. PFEFFER,¹ R.E. SHERRIFF,² C.W. LITTON,² R.L. JONES,² C.E. STUTZ,² and D.C. LOOK³
1--Army Research Lab, AMSRC-EP-EC, Fort Monmouth, NJ 07703-5601. 2--Wright Laboratory-WL/ELR, WPAFB, OH. 3--Wright State University, Dayton, OH.

KEY WORDS GaAs/AlGaAs, GaAs/InGaP, high electron mobility transistor (HEMT), pseudo-morphic high electron mobility transistor (PHEMT), organometallic vapor phase epitaxy (OMVPE)

Symmetric -doped InGaP and AlGaAs PHEMT structures have been grown by organometallic vapor phase epitaxy with properties that approach those of MBE grown AlGaAs structures. The 300 and 77K carrier concentrations for the InGaP PHEMT were 2.72 and 2.56 x 10¹² cm^-2 and the mobilities were 5,920 and 22,000 cm²/V·s. These excellent values suggest that problems associated with switching the anion at the channel heterojunction have been overcome. The corresponding values for the AlGaAs PHEMT were 2.51 and 2.19 x 10¹² cm^-2 and 6,500 and 20,400 cm²/V.s. The uniformity in the indium concentration in the InGaAs layer as determined by photoluminescence, photoreflection, double crystal x-ray diffraction, and Rutherford backscattering was found to be good, but the percent In in the AlGaAs pseudo-morphic high electron mobility transistor (PHEMT) was less than that in the InGaP PHEMT even though the programmed values were the same. The uniformity in the doping distribution as determined by secondary ion mass spectroscopy and electrochemical capacitance-voltage measurements was found to be good, but it decreased with distance from the center of the susceptor. Also, most of the dopants in the -doped InGaP and AlGaAs layers were activated.

Thermodynamic Modeling of As and P Incorporation in Ga_xIn_1-xP_yAs_1-y Epitaxial Layers Grown by Organometallic Vapor Phase Epitaxy
A.S. JORDAN
AT&T Bell Laboratories, Murray Hill, NJ 07974.

KEY WORDS GaInPAs, organometallic vapor phase epitaxy (OMVPE), thermodynamic modeling

The quaternary epitaxial film Ga_xIn_1-xP_yAs_1-y (Q) lattice-matched to InP is the active layer in lasers emitting between 1.1 and 1.55 µm. In this paper, we present a thermodynamic analysis of the group V incorporation in Q layers prepared by organometallic vapor phase epitaxy. We have recently given an equilibrium description of the combined pyrolysis of AsH₃ and PH₃ for any input flow rate and H₂ dilution as a function of growth temperature and total pressure, p_tot. To extend the treatment to gas-solid equilibrium, the Q solid is considered to be a quaternary regular solution subject to the constraint of mixing on both sublattices, for which activities were previously published. Knowing the free-energy of formation of the four bounding binary compounds, a root for y_P at a given temperature, input flow rates and p_tot is obtained by iteration that stops at values of p_As4 and p_P4 simultaneously satisfying the free-energies of formation and the gas flow material balance as well as the site conservation constraint. At a constant p_tot in complete thermodynamic equilibrium, y_P slowly increases with temperature (800-1200K). Taking into account the incomplete decomposition of PH₃ and considering the undecomposed fraction of PH₃ as an "inert" gas, the analysis shows a rapid rise in y_P with temperature in the deposition zone. Clearly, to attain the desirable thermodynamic regime at, say, ~650°C, the use of an alternative source, such as tertiarybutylphosphine, is desirable. We present the solid composition, y_P, as a function of temperature and PH₃ flow rate for realistic parameters for Q materials emitting between 1.1-1.55 µm. We also show the predicted lattice mismatch and emission wavelength associated with y_P. A preliminary comparison with experimental data obtained in our laboratory is in reasonable accord with the calculated results.

Metalorganic Vapor Phase Epitaxial Growth of GaInAsP/GaAs
A. KNAUER, G. ERBERT, S. GRAMLICH, A. OSTER, E. RICHTER, U. ZEIMER, and M. WEYERS
Ferdinand-Braun-Institut für Höchstfrequenztechnik Berlin, Rudower Chaussee 5, D-12489 Berlin, Germany.

KEY WORDS Doping, epitaxy, GaAs, GaInAsP, metalorganic vapor phase epitaxy (MOVPE), ordering

Ga_xIn_1-xAs_yP_1-y lattice matched to GaAs has been grown by low pressure metalorganic phase vapor epitaxy over the entire compositional range. At T_G = 670°C broad peaks of low intensity are observed in the 10K photoluminescence for y = 0.2-0.4 due to the predicted miscibility gap in this compositional region. An increase in growth temperature leads to a smaller miscibility gap. The band gap as well as the morphology show a strong dependence on substrate misorientation. The smoothest GaInAsP surfaces are obtained on exact oriented substrates. For the ternary GaInP the surface roughness is correlated to the degree of ordering in the temperature range of 600 to 750°C. The smallest band gap together with the smoothest surface is obtained on (100) 2° off to (111)B. Ordering effects are also observed in the quaternary GaInAsP. Broad-area lasers processed from the grown layers show high slope efficiency (0.9 W/A) and low internal losses (<3 cm^-1).

Evaluation and Optimization of Large Area III-V Epitaxial Thickness Uniformity Using a Fabry-Perot Microcavity Test Structure
QING. S. PADUANO,¹ DAVID WEYBURNE,² FENG LU,² and R. BHAT³
1--Kopin Corporation, Taunton, MA 02780. 2--USAF Rome Laboratory, Hanscom AFB, MA 01731. 3--Bellcore, Red Bank, NJ 07701.

KEY WORDS Fabry-Perot test structure, GaAs/AlAs, optical reflectivity mapping

We report a technique for simply and conveniently measuring epilayer thickness uniformity to 0.5% over an entire wafer. The technique requires epitaxial growth of a Fabry-Perot microcavity test structure. Mapping is performed by measuring the wavelength-dependent optical reflectivity at different points on the wafer and then fitting the reflectivity data to deduce the thickness uniformity. The mapping technique was used to determine the optimal growth conditions in a vertical rotating disk reactor that resulted in better than ±1% uniformity over a 2 inch wafer. The high precision of the optical reflectivity mapping technique can provide information not easily obtained with other techniques. For example, we show that the presence of wafer flat adversely affects the thickness uniformity.

Growth of Ga_xIn_1-xAs_1-ySb_y Alloys by Metalorganic Chemical Vapor Deposition
LI SHUWEI, JIN YIXIN, ZHOU TIANMING, ZHANG BAOLIN, NING YONGQIANG, JIANG HONG, and YUAN GUANG
Chang Chun Institute of Physics, Academia Sinica, 130021 Chang Chun, P.R. China.

KEY WORDS GaInAsSb, metalorganic chemical vapor deposition (MOCVD), scanning electron acoustic microscopy (SEAM)

The quaternary GaInAsSb alloy system with direct band gaps adjustable in wavelength from 1.7 to 4.3µm, which may provide the basis for emitters and detectors over this entire region, was studied. Alloys of GaInAsSb were grown lattice-matched on GaSb substrates by metalorganic chemical vapor deposition using a conventional atmospheric pressure horizontal reactor. The properties of the GaInAsSb alloys were characterized by single crystal x-ray rocking curves, the double crystal x-ray rocking curves, the photoluminescence and infrared absorption. A preliminary study of the capabilities of scanning electron acoustic microscopy in the characterization of GaInAsSb alloy has been made, some observations are briefly compared with scanning electron microscopy.

Low Temperature Growth and Planar Doping of ZnSe in a Plasma-Stimulated LP-MOVPE System
W. TAUDT, B. WACHTENDORF, F. SAUERLÄNDER, H. HAMADEH, S. LAMPE, and M. HEUKEN
Institut für Halbleitertechnik, RWTH Aachen, Templergraben 55, D-52056 Aachen, Germany.

KEY WORDS Metalorganic vapor phase epitaxy (MOVPE), plasma activated nitrogen, planar doping, ZnSe:N

In a low-pressure metalorganic vapor phase epitaxy process, we used dc-plasma activated nitrogen to dope ZnSe, grown with ditertiarybutylselenide and dimethylzinc-triethylamine. The nitrogen concentration of up to 2x10¹⁸ cm^-3 in the doped layers can be adjusted by the growth temperature, the dc-plasma power, and the N₂ dopant flow. Due to the high n-type background carrier concentration of the order of 10¹⁷ cm^-3 in undoped samples, the doped layers show n-type conductivity or were semi-insulating because of an additional compensation by hydrogen incorporated with a concentration of the order of 10¹⁸ cm^-3. A planar doping scheme was applied to reduce this hydrogen incorporation by one order of magnitude, although H₂ was used as carrier gas.

Effect of Se-doping on Deep Impurities in Al_xGa_1-xAs Grown by Metalorganic Chemical Vapor Deposition
J.C. CHEN, Z.C. HUANG, BING YANG, H.K. CHEN, TAO YU, and KUN-JING LEE
Department of Electrical Engineering, University of Maryland, Baltimore, MD 21228.

KEY WORDS AlGaAs, metalorganic chemical vapor deposition (MOCVD), Se-doping

We have studied the effect of Se-doping on deep impurities in Al_xGa_1-xAs (x = 0.2~0.3) grown by metalorganic chemical vapor deposition (MOCVD). Deep impurities in various Se-doped Al_xGa_1-xAs layers grown on GaAs substrates were measured by deep level transient spectroscopy and secondary ion mass spectroscopy. We have found that the commonly observed oxygen contamination-related deep levels at E_C-0.53 and 0.70 eV and germanium-related level at E_C-0.30 eV in MOCVD grown Al_xGa_1-xAs can be effectively eliminated by Se-doping. In addition, a deep hole level located at EV + 0.65 eV was found for the first time in Se-doped Al_xGa_1-xAs when Se is greater than or equal to 2x10¹⁷ cm^-3 or x t less than 5X10¹² cm^-3, detection limit) Al_0.22Ga_0.78As layer was achieved. A p-type Al_0.2Ga_0.8As layer with a low deep level density was also obtained by a (Zn, Se) co-doping technique.

Effect of Bragg Reflector on the Threshold Current Density in AlGaInP Visible Laser
M.S. OH, N.H. KIM, C.H. LEE, H.S. PARK, J.Y. KIM, G. PAK, and T.I. KIM
Materials & Devices Research Center, Samsung Advanced Institute of Technology, P.O. Box 111, Suwon, Korea.

KEY WORDS AlGaInP, Bragg reflector, GaInP, laser, threshold current

The GaInP/AlGaInP layers are known as attractive materials for 600 nm band laser diodes. In this paper, a Bragg reflector between GaAs substrate and n-cladding layer was applied for the reduction in the lasing threshold. In a SCH-MQW structure, a Bragg reflector was composed of alternating /4n layers of AlAs and AlGaAs layers, 12.5 pairs. The effect of Bragg reflector on the threshold current and spontaneous emission intensity was appreciable because most of spontaneously emitted photons were reflected from a Bragg reflector and carriers were regenerated in the GaInP active layer.

Oxygen Incorporation, Photoluminescence, and Laser Performance of AlGaAs Grown by Organometallic Vapor Phase Epitaxy
B.D. SCHWARTZ, R.S. SETZKO, J.S. MOTT, S.H. MACOMBER, and J.J. POWERS
Hughes Danbury Optical Systems, Inc., Wooster Heights Road, Danbury, CT 06810-7589.

KEY WORDS AlGaAs, laser diodes, oxygen, photoluminescence

Photoluminescence (PL) of separate confinement heterostructure, single quantum well (SCH-SQW) laser material provides a quantitative evaluation of the quality of AlGaAs grown by organometallic vapor phase epitaxy. There is a good correlation between the oxygen level in the quantum well confining layers measured by secondary ion mass spectroscopy, quantum well PL efficiency, and laser threshold current. When oxygen was reduced from 2.0 x 10¹⁸ cm^-3 to 1.5 x 10¹⁷ cm^-3, the PL intensity increased by a factor of 12, and the threshold current density was improved from 1300 to 240 A/cm² for a 100 x 600 µm device. Oxygen levels were decreased by using a higher growth rate, shorter interface pause time, higher V/III ratio, and an arsine purifier.

Growth Of High-Quality GaSb By Metalorganic Vapor Phase Epitaxy
T. KOLJONEN, M. SOPANEN, H. LIPSANEN, and T. TUOMI
Optoelectronics Laboratory, Helsinki University of Technology, FIN-02150 Espoo, Finland.

KEY WORDS Gallium antimonide, Hall mobility, metalorganic vapor phase epitaxy (MOVPE), photoluminescence

The growth of nominally undoped GaSb layers by atmospheric pressure metalorganic vapor phase epitaxy on GaSb and GaAs substrates is studied. Trimethylgallium and trimethylantimony are used as precursors for the growth at 600°C in a horizontal reactor. The effect of carrier gas flow, V/III-ratio, and trimethylgallium partial pressure on surface morphology, electrical properties and photoluminescence is investigated. The optimum values for the growth parameters are established. The carrier gas flow is shown to have a significant effect on the surface morphology. The optimum growth rate is found to be 3-8 µm/h, which is higher than previously reported. The 2.5 µm thick GaSb layers on GaAs are p-type, having at optimized growth conditions room-temperature hole mobility and hole concentration of 800 cm² V^-1 s^-1 and 3^.10¹⁶ cm^-3, respectively. The homoepitaxial GaSb layer grown with the same parameters has mirror-like surface and the photoluminescence spectrum is dominated by strong excitonic lines.

The Contraction of Lattice Constant and the Reduction of Growth Rate in p-InGaAs Grown by Organometallic Vapor Phase Epitaxy
JEONG SOO KIM, SEUNG WON LEE, HYUNG MUN KIM, DAE KON OH, HEUNG RO CHOO, DONG HOON JANG, HONG MAN KIM, KWANG EUI PYUN, and HYUNG MOO PARK
Semiconductor Division, ETRI, Yusong P.O. Box 106, Taejon, 305-606, Korea.

KEY WORDS Diethylzinc, InGaAs, lattice constant, organometallic vapor phase epitaxy (OMVPE)

We have investigated the effect of diethylzinc (DEZn) on the lattice constant and the growth rate of InGaAs. Introducing DEZn for p-type doping induces the contraction of lattice constant and the reduction of growth rate compared to undoped InGaAs. Depletion of indium is responsible for these effects. These effects are reduced at lower growth temperatures or at lower growth pressures. From the observed effects of the growth temperatures and the growth pressures on the contraction of the lattice constant, it is concluded that depletion of indium occurs in the gas phase.

Monitoring of MOCVD Reactants by UV Absorption
K.C. BAUCOM, K.P. KILLEEN, and H.K. MOFFAT
Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185.

KEY WORDS Bubbler efficiency, metalorganic chemical vapor deposition (MOCVD) reactants, UV absorption

In this paper, we describe how UV absorption measurements can be used to measure the flow rates of metalorganic chemical vapor deposition (MOCVD) reactants. This method utilizes the calculation of UV extinction coefficients by measuring the total pressure and absorbance in the neat reactant system. The development of this quantitative reactant flow rate monitor allows for the direct measurement of the efficiency of a reactant bubbler. We demonstrate bubbler efficiency results for TMGa, and then explain some discrepancies found in the TMAl system due to the monomer to dimer equilibrium. Also, the UV absorption spectra of metalorganic and hydride MOCVD reactants over the wavelength range 185 to 400 nm are reported.

Metalorganic Chemical Vapor Deposition Growth of High Optical Quality and High Mobility GaN
B.P. KELLER,¹ S. KELLER,¹ D. KAPOLNEK,¹ W.-N. JIANG,¹ Y.-F. WU,¹ H. MASUI,² X. WU,¹ B. HEYING,¹ J.S. SPECK,¹ U.K. MISHRA,¹ and S.P. DENBAARS¹
Electrical and Computer Engineering and Materials Departments, University of California, Santa Barbara, CA 93106. 2--Visiting Researcher Stanley Electric Co., Ltd., Yokohama, Kanagawa, Japan.

KEY WORDS GaN, metalorganic chemical vapor deposition (MOCVD), photoluminescence, sapphire

Hall mobilities as high as 702 and 1230 cm²/Vs at 300 and 160K along with low dislocation densities of 4.0 x 10⁸ cm^-2 have been achieved in GaN films grown on sapphire by metalorganic chemical vapor deposition. High growth temperatures have been established to be crucial for optimal GaN film quality. Photoluminescence measurements revealed a low intensity of the deep defect band around 550 nm in films grown under optimized conditions.

A New Buffer Layer for MOCVD Growth of GaN on Sapphire
X. LI, D.V. FORBES, S.Q. GU, D.A. TURNBULL, S.G. BISHOP, and J.J. COLEMAN
Microelectronics Laboratory, University of Illinois, Urbana, IL 61801.

KEY WORDS AlN buffer layer, double buffer layer, GaN, GaN buffer layer, metalorganic chemical vapor deposition (MOCVD), sapphire substrates

High quality GaN films have been grown on sapphire substrates (C face and A face) by atmospheric pressure metalorganic chemical vapor deposition (MOCVD) using a new buffer layer. With our reactor configuration and growth parameters, a GaN film grown on a single GaN buffer layer appears opaque with high density of hexagonal pits. Using a single AlN buffer layer results in extremely nonuniform morphology with mirror-like areas near the edge of the substrates and opaque areas in the center. The double buffer layer we report here, with GaN as the first layer and AlN as the second, each with an optimized thickness, leads to mirror-like films across the entire substrate. Scanning electron microscopy, photoluminescence, x-ray diffraction, and van der Pauw geometry Hall measurement data are presented to establish the quality of our films. The mechanism for this new buffer layer is also discussed.

Large Scale Production of Indium Antimonide Film for Position Sensors in Automobile Engines
EGBERT WOELK,¹ HOLGER JÜRGENSEN,¹ RANDY ROLPH,² and TIM ZIELINSKI²
1--AIXTRON GmbH, Kackertstr. 15-17, D-52072 Aachen, Germany. 2--Hughes Aircraft Company, Microwave Products Division 24120 Garnier Street, Torrance, CA 90509-2940.

KEY WORDS InSb, GaAs substrates, magnetoresistive sensors, metalorganic vapor phase epitaxy (MOVPE)

We use low pressure MOVPE to grow indium antimonide films on groups of eight 3 inch GaAs wafers per run. The films are used for the production of magnetoresistive position sensors for the car industry. To meet the narrow specifications for automotive components, the standard deviation of the sheet resistivity, and the thickness of the films have been reduced below 1.5%. This uniformity is the result of an optimization process encompassing the determination of the best susceptor temperature and the optimum flow. The gas velocity was found to have a large impact on the uniformity of the layers. Rotation of the wafers and the use of an optimum gas velocity results in extremely uniform layers.

Carbon Doped GaAs Grown in Low Pressure-Metalorganic Vapor Phase Epitaxy Using Carbon Tetrabromide
E. RICHTER, P. KURPAS, D. GUTSCHE, and M. WEYERS
Ferdinand-Braun-Institut für Höchstfrequenztechnik, Rudower Chaussee 5, D-12489 Berlin, Germany.

KEY WORDS CBr4, carbon doping, GaAs, hydrogen passivation, metalorganic vapor phase epitaxy (MOVPE), photoluminescence (PL)

Carbon tetrabromide was used as carbon source for heavily p-doped GaAs in low pressure metalorganic vapor phase epitaxy (MOVPE). The efficiency of carbon incorporation was investigated at temperatures between 550 and 670°C, at V/III ratios from 1 to 50 and carbon tetrabromide partial pressures from 0.01 to 0.03 Pa. Hole concentrations from 8 x 10¹⁷ to 5 x 10¹⁹ cm^-3 in as-grown layers were obtained. After annealing in nitrogen atmosphere at 450°C, a maximum hole concentration of 9 x 10¹⁹ cm^-3 and a mobility of 87 cm²/Vs was found. At growth temperatures below 600°C, traces of bromine were detected in the layers. Photoluminescence mapping revealed an excellent doping homogeneity. Thus, CBr₄ is found to be a suitable carbon dopant source in MOVPE.

REGULAR ISSUE PAPERS

KEY WORDS Extended defects, GaAs/Ge heterostructure, interface diffusion, metalorganic vapor phase epitaxy (MOVPE), surface morphology

GaAs epitaxial layers have been grown on (001) 6° off-oriented toward (110) Ge substrates by metalorganic vapor phase epitaxy. In order to study the influence of V/III ratio on the growth mechanisms and the structural properties of the layers, the input flow of arsine was changed over a wide range of values, while keeping constant all other experimental settings. Optical microscopy in the Nomarski contrast mode, x-ray topography and high resolution diffractometry, transmission electron microscopy and Rutherford backscattering have been used to investigate the epilayers. It has been found that the growth rate increases and the surface morphology worsens with increasing V/III ratio. The abruptness of the layer-substrate interface has also been found to strongly depend on the V/III ratio, the best results being obtained under Ga-rich conditions. The main structural defects within the layers are stacking faults and misfit dislocations. Layers grown under As-rich conditions only contain stacking faults, probably originated by a growth island coalescence mechanism, whereas layers grown under Ga-rich conditions contain both misfit dislocations and stacking faults generated by dissociation of threading segments of interfacial dislocations. In spite of the different defects, the strain relaxation has been found to follow the same trend irrespective of the V/III ratio. Finally, the relaxation has been found to start at a thickness exceeding the theoretical critical value.

Evidence for Reductive Elimination of H₂ in the Decomposition of Primary Arsines
DOUGLAS F. FOSTER, CHRISTOPHER GLIDEWELL, GORDON R. WOOLLEY, and DAVID J. COLE-HAMILTON
School of Chemistry, University of St. Andrews, St. Andrews, Fife, KY16 9ST, Scotland.

KEY WORDS Decomposition mechanisms, metalorganic vapor phase epitaxy (MOVPE), phenylarsine, t-butylarsine

The decomposition of o-CH₃C₆H₄AsD₂ (o-tolyl AsD₂) in the gas phase at 900K gives toluene with 0-3 D atoms in the methyl group and/or D on the ortho carbon. These experimental data, together with calculations carried out in the PM3 system show that the only low energy pathway for decomposition of o-tolylAsD₂ involves loss of D₂ followed by reaction of o-tolylAs with intact o-tolylAsD₂ to give o-tolylAsD*. o-tolylAsD* can reductively eliminate toluene or can undergo a rearrangement to o-HDAsC₆H₄CH₂* for which the calculated free energy of activation at 900K is very similar to that for reductive elimination, hence explaining the multiple deuteriation of the methyl group of toluene. Calculations on the decomposition of ^tBuAsH₂ show that this too decomposes by loss of H₂ to give ^tBuAs with a very low free energy of activation. ^tBuAs decomposes via -H abstraction to 2-methylpropene and AsH. There is no unimolecular process with a low free energy of activation that leads to 2-methylpropane, so it is proposed that this product arises mainly from bimolecular H transfer from ^tBuAsH₂ to ^tBuAs to give ^tBuAsH* which can lose 2-methylpropene or ^tBu*. ^tBu* abstracts H from an AsH species to give 2-methylpropane. A number of experimental results on the decomposition of ^tBuAsH₂ are rationalized in terms of these mechanistic pathways.

Microstructural Study of the Effect of an Excess of Y₂BaCuO₅ and BaSnO₃ Doping on the Texturing Process of YBa₂Cu₃O_7-x Bulk Superconductors
M.P. DELAMARE, I. MONOT, J. WANG, and G. DESGARDIN
Laboratoire CRISMAT, ISMRa, Bd. du Marechal Juin, 14050 Caen, Cedex France.

KEY WORDS >BaSnO3, superconductor, texturation

Melt texture process of YBCO leads to a YBa₂Cu₃O_7-x matrix where Y₂BaCuO₅ particles are observed. The Y₂BaCuO₅ inclusions size and distribution depend upon several parameters: YBa₂Cu₃O_7-x grain size in the presintered, heating rate, dopants. The influence of an excess of Y₂BaCuO₅ and/or BaSnO₃ on these Y₂BaCuO₅ particles are observed in the liquid phase and in the texture domain. According to the dopant used, two kinds of coarsening of Y₂BaCuO₅ can be observed: an isotropic and an anisotropic. The control of the distribution of Y₂BaCuO₅ particle size is of primary interest to improve the efficiency of the MTG process. In particular large cooling rate (5°C/h) during the texture formation could be used by adding Y₂BaCuO₅ + BaSnO₃ to YBa₂Cu₃O_7-x composition.

Defect Structures in Silicon Merged Epitaxial Lateral Overgrowth
SRIKANTH B. SAMAVEDAM,¹ ERIC P. KVAM,¹ ABULE E. KLABIR,² and GEROLD W. NEUDECK²
1--School of Materials Engineering, Purdue University, West Lafayette, IN 47906. 2--School of Electrical Engineering, Purdue University, West Lafayette, IN 47906.

KEY WORDS Electronic quality, epitaxial lateral overgrowth, merge defect, silicon

Merging of two epitaxial lateral overgrowth fronts has been achieved to produce thin silicon-on-insulator (SOI) structures. The electronic quality of the material is generally of high quality; however, at the merger interface are defects associated with improper merging. Defects at the oxide/silicon interface and the merging interface were characterized using transmission electron microscopy. Device performance indicated the need for a process modification to improve the material quality for potential electronic applications.

Characterization of Low Range GaAs
MICHAEL Y. FRANKEL,¹ ADRIANA GIORDANA,² and D. SCOTT KATZER²
1--Optical Sciences Division, Naval Research Lab, Washington, DC 20375. 2--Electronics Science and Technology Division, Naval Research Lab, Washington, DC 20375.

KEY WORDS Anneal, low range GaAs, low temperature GaAs, molecular beam epitaxy (MBE)

We present the results of a study of GaAs material grown at substrate temperatures below 250°C (low range GaAs) by molecular beam epitaxy. This material is amorphous and highly resistive and can be converted to single crystal through annealing process. The crystallization process is investigated by transmission electron microscopy, reflection high-energy electron diffraction, and double-crystal x-ray diffraction techniques.

Minority Carrier Lifetime in Doped and Undoped Epitaxially Grown n-type Cd_xHg_1-xTe
S. BARTON, D. DUTTON, P. CAPPER, C.L. JONES, and N. METCALFE
G.E.C. Marconi Infrared Ltd., P.O. Box 217, Southampton, S015 OEG England.

KEY WORDS CdxHg1-xTe (CMT), epitaxial, lifetime, passivation, n-type

The performance of infrared detectors made from Cd_xHg_1-xTe (CMT) is related to the lifetime of minority carriers in the material. Both photoconductive and photovoltaic devices require long lifetimes for high performance. This paper compares lifetime measurements on epitaxially grown CMT layers which have been isothermally annealed to minimize the vacancy concentration and are n-type due to native defects, residual impurities, or deliberately added dopants. Layers grown by liquid phase epitaxy (LPE), metalorganic vapor phase epitaxy (MOVPE), and molecular beam epitaxy (MBE) have been considered, in all cases the same measurement system was used under the same low injection conditions. All layers were of compositions required for operation in the 8 to 14µm wavelength range. Comparisons have been made between undoped and indium doped LPE layers and undoped and iodine doped MOVPE layers. It was hoped that a deliberately introduced donor impurity would give better control of the n-type properties. The effect of passivation on the measurement of lifetime has also been considered, the results showing that a surface with a native oxide is required to obtain the true bulk lifetime as has been seen previously for bulk material.