JOURNAL OF ELECTRONIC MATERIALS
	ABSTRACTS Volume 25, Number 4, April 1996 This Month Featuring: Proceedings of the symposium on Advances in Indium Phosphide, Related Materials and Processing Part II: Processing and Characterization. View April 1996 Table of Contents.

SPECIAL ISSUE PAPERS

A driving force for optical technologies is the promise of speed and bandwidth in network applications. Discrete devices, with record breaking performance are only indicators of functional optoelectronic circuit and system potential. In turn, new processing tools that can enable photonic integration have become essential. It was strongly evident that the processing area is experiencing a resurgence of research in several areas particularly passivation and control of surfaces and interfaces. A common goal of many researchers seems to be the development of in-situ processing. In one instance, the long-lived problem of a strongly pinned Fermi level at the InP surface was analyzed and addressed by an in-situ electrochemical etching and metalization process, thus enabling unencumbered Schottky barrier formation on an unpinned surface. Another simple but effective technique, passivates the surface and controls pinning with a low temperature CdS-thiourea chemical treatment. The process effectively removes native oxides, provides a barrier to oxide regrowth, and forms III-S bridge bonds reducing traps due to P-vacancies. In-situ processing techniques are further advanced by the use of chemical beam etching combined with CBE and GSMBE growth techniques. New enhanced device fabrication techniques such as fusion and flipped epitaxial transfer passivation were presented for a variety of electronic and optoelectronic devices. Other advances included InP-lasers directly bonded on Si and photodetectors with fused wavelength selective films enabling custom integrated device and OEIC design. Formation of multiple laser mirrors in a novel multiple reflection micro cavity laser was achieved by vertical chemical etching and highly reliable passivation techniques for electron devices were discussed from a standpoint of practical application.

The 1996, eighth international IPRM conference venue will be Schwaebisch Gmuend, Germany, at the Conference Center Stadtgarten, from April 22 to 25th.

JOE LORENZO, OSAMU WADA, HAJIME ASAHI, and HIDEKI HASEGAWA
Guest Editors

High Electron Mobility 18300 cm²/V^.s in the InAlAs/InGaAs Pseudomorphic Structure Obtained by Channel Indium Composition Modulation
T. NAKAYAMA, H. MIYAMOTO, E. OISHI, and N. SAMOTO
Kansai Electronics Research Laboratories, NEC Corporation, 2-9-1 Seiran, Otsu, Shiga 520, Japan.

KEY WORDS Electron mobility, InAlAs, InAs, InGaAs, heterojunction field effect transistor (HJFET), pseudomorphic structure

The highest electron mobility yet reported for an InP-based pseudomorphic structure at room temperature, 18300 cm²/V^.s, has been obtained by using a structure with an indium composition modulated channel, namely, In_0.53Ga_0.47As/In_0.8Ga_0.2As/ InAs/In_0.8Ga_0.2As/In_0.53Ga_0.47As. Although the total thickness of the high In-content layers (In_0.8Ga_0.2As/InAs/In_0.8Ga_0.2As) exceeds the critical thickness predicted by Matthews theory, In_0.8Ga_0.2As insertion makes it possible to form smooth In_0.53Ga_0.47As/In_0.8Ga_0.2As and In_0.8Ga_0.2As/InAs heterointerfaces. This structure can successfully enhance carrier confinement in the high In-content layers. This superior carrier confinement can be expected to lead to the highest yet reported electron mobility.

Reliability of AlInAs/InGaAs/InP HEMT with WSi Ohmic Contacts
H. SASAKI,^1,2,3 K. YAJIMA,¹ N. YOSHIDA,² T. ISHIDA,² R. HATTORI,² T. SONODA,² O. ISHIHARA,² S. TAKAMIYA,² R. KONISHI,³ and K. ANDO³
1--Quality Assurance Department, Mitsubishi Electric Corporation, 4-1, Mizuhara Itami City, Hyogo 664, Japan. 2--Optoelectronic & Microwave Devices Lab, Mitsubishi Electric Corporation, 4-1, Mizuhara Itami City, Hyogo 664, Japan. 3--Faculty of Engineering, Tottori University, 4-101, Koyama, Tottori 680, Japan.

KEY WORDS AlInAs/InGaAs/InP HEMT, degradation, EDX, life test, ohmic contact, WSi, X-TEM

We have investigated the degradation mechanism of Al_0.48In_0.52As/In_0.53Ga_0.47As/InP high electron mobility transistors (HEMTs) using WSi ohmic electrodes. Cross-sectional transmission electron microscopy (TEM) observation and energy dispersive x-ray (EDX) analysis reveal impurities diffusion of gate electrode (titanium: Ti) and fluorine (F) in the AlInAs layer after a high temperature (T_a = 170°C operating life test for 500h. The decrease of drain current (I_ds) during life test shows linear dependence on square root of aging time. It suggests that the degradation is controlled by a diffusion mechanism. Hence, the estimated degradation mechanism of this device is related with decrease of carrier concentration in the epitaxial layer by these diffused impurities. On the other hand, TEM and EDX show no degradation of WSi/InGaAs interface after aging. Therefore, the WSi electrode for this type of HEMT demonstrates excellent high stability under the accelerated operating life test.

Impurity-Induced Disordering of AlGaInAs Quantum Wells by Low Temperature Zn Diffusion
KAZUHIKO ITAYA,¹ MARK J. MONDRY,² PHILIP D. FLOYD,² LARRY A. COLDREN,² and JAMES L. MERZ³
1--Department of Electrical and Computer Engineering, University of California, Santa Barbara, Santa Barbara, CA 93106. On leave from Toshiba Co., Japan, Currently, Toshiba Materials and Devices Laboratories, 1 Komukai Toshibacho, Saiwai-ku, Kawasaki 210, Japan. 2--Department of Electrical and Computer Engineering, University of California, Santa Barbara, Santa Barbara, CA 93106. 3--Permanent address: Department of Electrical Engineering, University of Notre Dame, Notre Dame, IN 46556-5637.

KEY WORDS 1.5 µm, AlGaInAs, diffusion, disordering, laser diode, multi-quantum well (MQW), strain, Zn

We investigated impurity-induced disordering (IID) in AlGaInAs multi-quantum wells (MQWs) on InP substrate by Zn diffusion under low temperature conditions. Blue-shift of band-gap energy of lattice-matched AlGaInAs MQW on InP strongly depended on the temperature of Zn diffusion. The lattice-matched MQW was not completely disordered below 500°C. On the other hand, photoluminescence spectra from compressively strained AlGaInAs MQW, after disordering was independent of the temperature of Zn diffusion. Considerable disordering was observed in the strained MQW, which was saturated even at the low temperature of 400°C. The measured hole concentration of the Zn diffused layer at 400°C was as low as 3 x 10¹⁸cm^-3. The IID lasers were also fabricated and characterized. No significant increase in the optical loss due to the Zn diffusion was observed in these lasers.

Chemical Beam Etching of InP in GSMBE
J-L. GENTNER,¹ PH. JARRY,² and L. GOLDSTEIN²
1--Alcatel Alsthom Recherche, Route de Nozay, F-91460 Marcoussis (France). e-mail: gentner@aar.alcatel-alsthom.fr. 2--Alcatel Alsthom Recherche, Route de Nozay, F-91460 Marcoussis (France).

KEY WORDS Etching, InP, molecular beam epitaxy (MBE), PCl3, reflection high energy electron diffraction (RHEED)

Etching of InP using a beam of PCl₃ is demonstrated in a standard gas source molecular beam epitaxy machine. The principle of an atomic layer accurate end-point detection technique using in-situ reflection high energy electron diffraction is described and used to study the kinetics of PCl₃ etching. The etch rate is found proportional to the PCl₃ fluence and weakly dependent on the substrate temperature. The morphology of etched surfaces and the etch rate uniformity is compatible with the regrowth of high quality InGaAsP active structures and with the realization of etch and regrowth sequences controlled at the nm scale. Etch profiles at mask edges are defined by nearly perfect crystallographic facets with a very limited mask undercut (100 nm) due to the beam nature of the etching technique.

Morphological and Electrical Characterization of Al/Ni/n-InP Contacts with Tapered Insertion Ni-Layer
S. MIYAZAKI, T.-C. LIN, C. NISHIDA, H.T. KAIBE, and T. OKUMURA
Department of Electronics and Information Engineering, Tokyo Metropolitan University, 1-1, Minami-ohsawa, Hachiohji, Tokyo 192-03, Japan.

KEY WORDS Al/Ni contact, InP, scanning internal-photoemission microscopy, Schottky barrier height enhancement, tapered insertion Ni-layer

The addition of a thin Ni layer has improved the surface morphology of Al/n-InP contacts which show an enhanced Schottky barrier height (SBH) after rapid thermal annealing. In order to determine the optimum thickness of the insertion Ni layer, we have fabricated a unique sample in which the thickness of the insertion Ni layer tapered off in space. The improvement of the surface morphology as well as the SBH enhancement were realized by inserting 35 nm Ni layer annealed at rather low temperatures (around 450°C). The solid-phase reaction between Ni and InP might play an important role in the low-temperature formation of AlP which was responsible for the SBH enhancement.

A 1.3 µm Strained Quantum Well Laser on a Graded InGaAs Buffer with a GaAs Substrate
T. UCHIDA,¹ H. KURAKAKE,¹ H. SODA,² and S. YAMAZAKI¹
1--Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi 243-01, Japan. 2--Fujitsu Limited, 1015 Kamikodanaka, Kawasaki 211, Japan.

KEY WORDS Characteristic temperature, compositionally graded layer, InGaAs/GaAs, laser, lattice relaxation, metalorganic vapor phase epitaxy (MOVPE), quantum well (QW), Se

We grew a 1.3 µm strained-layer quantum well (SL-QW) laser with InGaP cladding layers on a lattice-relaxation buffer layer by metalorganic vapor phase epitaxy. For the lattice-relaxation buffer, we used a compositionally graded InGaAs/GaAs structure. The significantly reduced surface roughness of the InGaP cladding layers achieved by supplying a large amount of H₂Se enables CW operation of our 1.3 µm SL-QW laser. We achieved a low threshold current of less than 10 mA and a high characteristic temperature of 100K around room temperature.

Controlled Beam Dry Etching of InP by Using Br₂-N₂ Gas
SATOSHI OKU,¹ YASUO SHIBATA,¹ and KENICHI OCHIAI²
1--NTT Opto-electronics Laboratories, 3-1 Morinosato Wakamiya, Atsugi-shi, Kanagawa 243-01, Japan. 2--NTT Advanced Technology, 3-1 Morinosato Wakamiya, Atsugi-shi, Kanagawa 243-01, Japan.

KEY WORDS Bromine, corner mirror, dry etching, indium phosphide, nitrogen, reactive ion beam etching, secondary electron, waveguide

Indium phosphide dry etching is carried out using a reactive beam extracted from a Br₂-N₂ gas discharge plasma. Keeping the N₂ gas pressure constant at 0.23 mTorr, the Br₂ gas pressure was varied from 0 to 0.1 mTorr and the sample temperature was varied from 40 to 200°C. The etched shapes and etching rates are investigated in terms of the etching beam composition. Two distinct types of etching mechanisms come into play depending on the Br₂ gas pressure. Smooth vertical side walls and a temperature independent etching rate can be obtained at a Br₂ gas pressure of 0.04 mTorr or less and a temperature above 100°C, where the etching is induced by the ambient Br₂ gas species and N₂ beam. Undercut etching with a temperature dependent etching rate is seen at a Br₂ gas pressure of 0.07 mTorr or higher, where the etching beam contains both N₂ and Br₂ gas species. Neutralized Br species generated by the discharge of the Br₂ gas are shown to form the undercut. A waveguide corner mirror with a loss of less than 1 dB is made by using an etching beam with no neutralized Br species.

(NH₄)₂S_x-Treated InP(100) Surfaces Studied by Soft X-Ray Photoelectron Pectroscopy
S. MAEYAMA, M. SUGIYAMA, S. HEUN, and M. OSHIMA
NTT Interdisciplinary Research Laboratories, Midori-cho, Musashino-shi, Tokyo 180, Japan.

KEY WORDS GaAs, InP, (NH4)2Sx-treatment, photoelectron spectroscopy, soft x-ray, sulfur, surface passivation, synchrotron radiation

The sulfur chemical bonding state on (NH₄)₂S_x-treated InP(100) surfaces has been studied by S1s core-level photoelectron measurements using synchrotron radiation soft x-rays. The change in the sulfur chemical bonding states caused by rinsing with water and annealing in vacuum after the (NH₄)₂S_x-treatment was observed clearly in the S1s spectra. Four kinds of sulfur bonding states were resolved in the S1s spectrum of the as-treated surface. Only one sulfur bonding state was detected on the surfaces with and without the water rinse after annealing, indicating that the InP surfaces were terminated by the S-In bond. The effect of rinsing the (NH₄)₂S_x-treated InP surface is discussed by comparison with the (NH₄)₂S_x-treated GaAs surface.

Formation of PN_x/InP Structure by In Situ Remote Plasma Processes
YOSHIFUMI SAKAMOTO, TAKASHI SUGINO, TAKASHI MIYAZAKI, and JUNJI SHIRAFUJI
Department of Electrical Engineering, Faculty of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565, Japan.

KEY WORDS Barrier height, InP, MIS structure, phosphorus nitride, Schottky junction, surface Fermi level

In situ remote plasma processes consisting of removal of native oxide due to hydrogen (H₂) plasma, surface modification due to phosphine (PH₃) plasma and deposition of phosphorus nitride (PN_x) films due to decomposition of PH₃ by nitrogen (N₂) plasma have been developed. The insulating PN_x film with optical bandgap of 5.3eV and electrical resistivity of 3.7 x 10¹⁴ cm is obtained by remote plasma chemical vapor deposition. Au/PN_x/InP tunneling metal-insulator-semiconductor (MIS) type Schottky junction is formed by the in situ multiprocess. The effective barrier height is estimated to be as high as 0.83eV. Enhancement of the effective barrier height is due to both effects of the MIS structure and unpinning of the surface Fermi level.

Cadmium Sulfide Surface Stabilization for InP-Based Optoelectronic Devices
K. VACCARO, A. DAVIS, H.M. DAUPLAISE, S.M. SPAZIANI, E.A. MARTIN, and J.P. LORENZO
USAF Rome Laboratory, Optical Components Branch, Hanscom Air Force Base, MA 01731.

KEY WORDS III-V semiconductors, cadmium sulfide, InP, interface, MIS, passivation, Schottky barrier

Thin layers of chemical bath deposited cadmium sulfide were used to improve the surface and interface properties of InP and its latticed-matched III-V compounds. X-ray photoelectron spectroscopy indicates chemical reduction of surface oxides and the prevention of subsequent group III or V oxide formation. Photoluminescence spectra, measured between 1.0 and 1.3 µm, indicate a dramatic reduction in phosphorus vacancies following CdS treatment. Metal-insulator-semiconductor capacitors fabricated on n-type InP substrates with CdS interlayers display near-ideal quasi-static response and interface-state densities in the low 10¹¹/eVcm² range. Thin CdS layers were used to passivate the surface of InAlAs/InGaAs high electron mobility transistors and metal-semiconductor-metal photo detectors. After CdS treatment, Schottky diode barrier heights of 0.6eV were regularly obtained. For HEMTs, drain-to-gate current ratios of 8 x 10⁴ were observed after CdS treatment. For a new backside illuminated MSM design, the dark current of CdS-treated samples was reduced three orders of magnitude to below 1 nA.

Interfacial Layer in Homoepitaxial InP Grown by Organometallic Vapor Phase Epitaxy with TMIn and TBP
HIROYASU NAKATA,¹ KAZUO SATOH,¹ TYUZI OHYAMA,¹ YASUFUMI FUJIWARA,² YOUICHI NONOGAKI,² and YOSHIKAZU TAKEDA²
1--Department of Physics, Graduate School of Science, Osaka University, 1-16 Machikaneyama-cho, Toyonaka 560, Japan. 2--Department of Materials Science and Engineering, School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-01, Japan.

KEY WORDS Far-infrared, InP, interfacial layer, photoluminescence

The effects of interfacial layers with high impurity concentration on the properties of homoepitaxial InP layers have been studied by far-infrared (FIR) magnetoabsorption, in addition to dc mobility, Hall effect, and photoluminescence (PL) measurements. The layers are grown by organometallic vapor phase epitaxy with trimethylindium and tertiarybutylphosphine. Impurity absorption as well as cyclotron resonance is observed in the FIR measurements. Variations in the intensity of the resonance signals and the mobilities obtained from the linewidths of the cyclotron resonance are interpreted by a double layer model, i.e. a bulk layer with an interfacial layer. Carrier concentrations, dc mobilities, and PL intensities of both bound excitons and free excitons are also explained by the model.

Fabrication of InP-Based InGaAs Ridge Quantum Wires Utilizing Selective Molecular Beam Epitaxial Growth on (311)A Facets
H. FUJIKURA and H. HASEGAWA
Research Center for Interface Quantum Electronics and Graduate School of Electronics and Information Engineering, Hokkaido University, Sapporo 060, Japan.

KEY WORDS (311)A/(411)A facets, cathodoluminescnece (CL), InGaAs/InAlAs, molecular beam epitaxy (MBE), patterned InP substrate, photoluminescence (PL), ridge quantum wire, selective growth, scanning electron microscopy (SEM)

InP-based InGaAs/InAlAs ridge quantum wires were successfully fabricated by our new approach using selective molecular beam epitaxy (MBE). As the starting structures, array of InGaAs ridge structures composed of smooth (311)A facets were formed by MBE on mesa-patterned InP substrates. Prior to actual fabrication of the wires, MBE growth characteristics of In_0.53Ga_0.47As and In_0.52Al_0.48As layers on the starting structure were studied in detail. The results of growth experiments were then successfully applied to the fabrication of InGaAs ridge quantum wires with high spatial uniformity. Low temperature cathodoluminescence spectrum measured in response to spot excitation of wire region showed a strong light emission whose analysis indicated that it originates from InGaAs ridge quantum wire itself. In photoluminescence measurements, the emission from the wire had strong intensity even at room temperature, indicating that the wire crystal possesses excellent bulk and interface quality, and are largely free from nonradiative recombination centers.

Material and Electrical Characteristics of Iron Doped Pt-InAlAs Schottky Diodes Grown by LP-MOCVD
KYUSHIK HONG, DIMITRIS PAVLIDIS, and FRÉDÉRIC SÉJALON
Solid-State Electronics Laboratory, Department of Electrical Engineering and Computer Science, The University of Michigan, Ann Arbor, MI 48109-2122.

KEY WORDS Deep traps, InAlAs Schottky diodes, iron doping

InAlAs lattice-matched to InP is of great importance as a large bandgap material for various InP-based heterostructures device applications. However, growth of good quality InAlAs using metalorganic chemical vapor deposition (MOCVD) is relatively difficult due to the reactive nature of its aluminum sources. In this paper, we present the use of iron as a possible dopant to improve the electrical properties of MOCVD grown InAlAs. Time resolved photoreflectance was used to confirm the increase in trap levels with increased iron doping. The impact of iron doping on the electrical properties of devices was investigated using Pt-Schottky diodes fabricated on undoped and iron doped InAlAs materials. Low frequency noise measurements were also carried out to investigate the impact of iron incorporation on the noise characteristics of the devices. Although noise levels showed marginal difference between undoped and iron doped materials, iron doped InAlAs showed a Lorentzian component in the noise spectra which is not found in undoped materials. An activation energy of ~0.77eV was evaluated for traps introduced by iron incorporation using temperature dependent low frequency noise measurements.

Thermal Stability of Al_0.48In_0.52As/Ga_0.47In_0.53As/InP Heterostructure and its Improvement by Phosphidization
N. TAKAHASHI,¹ M. SHIOTA,¹ Y. ZHU,¹ M. SHIMIZU,¹ D. HIRATA,² Y. SAKAMOTO,² T. SUGINO,² and J. SHIRAFUJI²
1--Central Research Laboratories, SHARP Corporation, 2613-1 Ichinomoto, Tenri, Nara 632, Japan. 2--Department of Electrical Engineering, Faculty of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565, Japan.

KEY WORDS Compensation, damage, high electron mobility transistor (HEMT), InAlAs, molecular beam epitaxy (MBE), passivation, plasma

A drastic decrease in the sheet carrier concentration of modulation-doped Al_0.48In_0.52As/Ga_0.47In_0.53As/InP heterostructures has been observed after O₂ plasma treatment followed by thermal treatment up to 350°C. The decrease in sheet carrier concentration, which is speculated to be caused by both plasma damage and impurities penetrating from the surface of the epilayer, can be suppressed substantially by using PH₃ plasma treatment prior to the O₂ plasma and thermal treatments.

Low Temperature Grown Be-Doped InAlP Band Offset Reduction Layer to p-Type ZnSe
K. IWATA,¹ H. ASAHI,¹ T. OGURA,¹ J. SUMINO,¹ S. GONDA,¹ A. OHKI,² Y. KAWAGUCHI,² and T. MATSUOKA²
1--The Institute of Scientific and Industrial Research, Osaka University, 8-1, Mihogaoka, Ibaraki, Osaka 567, Japan. 2--NTT Opto-electronics Labns., Morinosato Wakamiya, Atsugi, Kanagawa 243-01, Japan.

KEY WORDS Band offset reduction layer, gas source molecular beam epitaxy (GSMBE), InAlP, ohmic contact, ZnSe

To solve the difficulty of achieving low resistance ohmic contact to p-type ZnSe, the use of an intermediate p-type InAlP layer to p-type ZnSe as a valence band offset reduction layer is studied by gas source molecular beam epitaxy. It is found that hole concentrations as high as 2 x 10¹⁸cm^-3 are easily obtained for p-type InAlP layers grown on GaAs even at low temperature of 350°C, although a higher Be cell temperature is required than that for a 500°C grown p-type InAlP due to the decreased electrical activity of Be in InAlP. Despite the very high Be concentrations, the Be precipitation/segregation is not observed. It was difficult to obtain the same hole concentration of InAlP layers grown on ZnSe as that on GaAs. However, the insertion of only several monolayers of GaAs between ZnSe and InAlP makes it possible to avoid faceting growth of InAlP and to improve the electrical properties of Be-doped InAlP grown on ZnSe. These results suggest that the Be-doped InAlP layer can be used as an intermediate layer to form the low resistance ohmic contact to p-type ZnSe.

New Low Contact Resistance Triple Capping Layer Enabling Very High G_m InAlAs/InGaAs HEMTs
K. HIGUCHI, M. MORI, M. KUDO, and T. MISHIMA
Central Research Lab., Hitachi, Ltd., 1-280 Higashi-koigakubo, Kokubunji, Tokyo 185, Japan.

KEY WORDS Contact resistance, high electron mobility transistor (HEMT), InP, nonalloyed electrodes

It has been demonstrated that a highly doped (Si:3 X 10¹⁹cm^-3) triple capping layer consisting of n⁺-In_0.53Ga_0.47As, n⁺-In_0.52Al_0.48As, and n⁺-In_0.53Ga_0.47As can remarkably reduce the parasitic source resistance in InP-based high electron mobility transistors (HEMTs). The analysis of the source resistance revealed that the resistance element at the n⁺-In_0.53Ga_0.47As/un-In_0.52Al_0.48As/un-In_0.53Ga_0.47As channel heterointerfaces was as large as 70% of the source resistance when nonalloyed ohmic electrodes were used. The highly doped triple capping layer reduces the resistance contribution of vertical conduction between the capping layer and 2DEG channel. A low source resistance of 0.57 mm and a low contact resistivity of 3 X 10^-5cm² were obtained for the HEMTs with the highly doped triple capping layer, which were 60% lower and one order of magnitude smaller than those for the HEMTs with a conventional single capping layer doped 5 X 10¹⁸cm^-3, respectively. These values were also 70 and 30% lower than those for the HEMTs with a highly doped (3 X 10¹⁹cm^-3) single capping layer, respectively. The low source resistance brings high peak extrinsic transconductance of 1 S/mm for a device with 0.4 µm long gate, which was 42% higher than the previously reported HEMTs with the same gate length.

A Novel Insulated Gate Technology for InGaAs High Electron Mobility Transistors Using Silicon Interlayer Based Passivation Technique
S. SUZUKI, S. KODAMA, H. TOMOZAWA, and H. HASEGAWA
Research Center for Interface Quantum Electronics and Department of Electrical Engineering, Hokkaido University, Sapporo 060, Japan.

KEY WORDS Capacitance-voltage (C-V), insulated gate high electron mobility transistor (IGHEMT), InGaAs, passivation

A novel insulated gate technology for InGaAs high electron mobility transistors (HEMT) is described. It utilizes a silicon interface control layer (Si ICL)-based passivation structure. By applying an HF surface treatment, the technology becomes applicable to the air-exposed surfaces of InGaAs and InAlAs. The basic metal-insulator-semiconductor structures were fabricated and characterized in detail by x-ray photoelectron spectroscopy analysis and capacitance-voltage measurements. The interface has been shown to be essentially free from interface states. InGaAs insulated gate HEMTs (IGHEMT) were then successfully fabricated. The fabricated recessed gate IGHEMTs have good gate control of the drain current with good pinch-off characteristics. A highest effective mobility of 2010 cm²/Vs was obtained. The devices show extremely low gate leakage currents below 1nA/mm.

Fabrication of 60 nm Pitch Ordered InP Pillars by EB-Lithography and Anodization
TOSHIYUKI TAKIZAWA, MASAFUMI NAKAHARA, EIJIRO KIKUNO, and SHIGEHISA ARAI
Research Center for Quantum Effect Electronics, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro-ku, Tokyo 152 Japan.

KEY WORDS Anodization, electron-beam lithography, InP triangular pillar structure, photoluminescence

We obtained ordered 60 nm pitch InP triangular vertical pillars with a high density of approximately 50% by combining electron-beam lithography and anodization techniques. For the lower dose condition of 2.3 X 10^-6 nC/dot, triangular pillars of 70% density were observed within 5% of the average pillar size (Fig. 2). Furthermore, using dry etching transfer onto SiO₂, we obtained ordered 40 nm pitch pillars and observed photoluminescence intensity comparable to that from bulk InP substrates, indicating negligible nonradiative recombination.

Photocurrent Anisotrophy in Compositional Modulated Superlattice of Long-Range Ordered Ga_0.5In_0.5P
TAKASHI KITA, AKIRA FUJIWARA, HIROSHI NAKAYAMA, and TANEO NISHINO
Department of Electrical and Electronics Engineering, Faculty of Engineering, Kobe University, 1-1 Rokkodai, Kobe 657, Japan.

KEY WORDS GaInP, ordering, photocurrent, superlattice

Photocurrent anisotropy of long-range ordered Ga_0.5In_0.5P alloys has been systematically investigated. The ordered Ga_0.5In_0.5P is a compositional modulated superlattice of Ga_0.5+/2In_0.5-/2P and Ga_0.5-/2In_0.5+/2P monolayer planes, where is a long-range order parameter. The photocurrent edge of the [110] polarization is lower than that of the []. The observed anisotropy in the photocurrent spectra is due to a crystal-field splitting at the valence-band maximum in ordered Ga_0.5In_0.5P. The anisotropy shows a continous variation as a function of . In order to make clear the effects of the valence-band splitting on the polarized photocurrent spectra, we performed theoretical calculations in which a distribution of in the epitaxial film and an order-parameter dependence of oscillator strength were considered. From these calculations, it is found that oscillator strength is a key parameter in the anisotropic character. The calculated results moderately agree with the measured data. Furthermore, the epitaxial thickness dependence of the anisotropic character in photocurrent was investigated.

Identification of Topmost Atom on InP (001) Surface by Coaxial Impact Collision Ion Scattering Spectroscopy
T. NISHIHARA,¹ M. SHINOHARA,¹ O. ISHIYAMA,¹ F. OHTANI,¹ M. YOSHIMOTO,² T. MAEDA,² and H. KOINUMA²
1--Keihanna Research Laboratory, Shimadzu Corporation, Hikaridai 3-9, Seikacho, Sorakugun, Kyoto 619-02, Japan. 2--Research Laboratory of Engineering Materials, Tokyo Institute of Technology, Nagatsuta 4259, Midoriku, Yokohama 226, Japan.

KEY WORDS Ar sputtering, coaxial impact collision ion scattering spectroscopy (CAICISS), indium phosphide, ion scattering spectroscopy, surface analysis

The topmost atom of InP (001) surfaces, which were annealed at temperatures between 300 and 550°C or sputtered with 1 keV Ar⁺ at 300°C in ultra high vacuum, has been directly identified by means of coaxial impact collision ion scattering spectroscopy (CAICISS). Time-of-flight spectra of the annealed InP (001) surface exhibited both In and P peaks in both [] azimuth and in [100] azimuth, which revealed that the topmost layer of annealed InP (001) was comprised of In-terminated and P-terminated surfaces. On the other hand, time-of-flight spectrum of the InP (001) sputtered at 300°C revealed only an In peak in [] azimuth and revealed both In and P peaks in [100] azimuth. This result indicates that the topmost layer on the Ar⁺-sputtered InP (001) surface was completely terminated by In atoms. Furthermore, we indicate that surface damage induced by this sputtering treatment is little. The azimuthal dependence of CAICISS intensity scattered from In and P showed twofold symmetry with respect to [100] direction, which originated from the zinc-blende structure.

Group-V Atoms Exchange Due to Exposure of InP Surface to AsH₃(+PH₃) Revealed by X-Ray CTR Scattering
M. TABUCHI,¹ N. YAMADA,¹ K. FUJIBAYASHI,¹ Y. TAKEDA,¹ and H. KAMEI²
1--Department of Materials Science and Engineering, School of Engineering, Nagoya University, Nagoya 464-01, Japan. 2--Opto-electronics R & D Laboratories, Sumitomo Electric Industries, Ltd., 1, Taya-cho, Sakae-ku, Yokohama 244, Japan.

KEY WORDS Atoms exchange, interface structure, OMVPE, synchrotron radiation, x-ray crystal truncation rod (CTR)

We conducted x-ray crystal truncation rod (CTR) measurements using synchrotron radiation to analyze the As atom distribution in InP to the order of 1 ML. The InP samples which were only exposed to AsH₃(+PH₃) and capped by InP were investigated to study the effect of the purge sequence. The purge sequence is unavoidable to grow heteroepitaxial layers by OMVPE and is considered to affect largely the structure of the interface. From the results of the measurement and the computer simulation, the distribution of P and As atoms of the order of 1 ML was discussed as functions of the exposing time. It was shown that the number of As atoms contained in the samples saturated when the AsH₃-exposure time is longer than 10s. Comparing the profiles of AsH₃-exposed samples with that of (AsH₃+PH₃)-exposed samples, it was found that the As distribution in the buffer layer was suppressed in (AsH₃+PH₃)-exposed samples. In order to obtain the sharp interfaces, the AsH₃-exposure time must be shorter than 0.5s.

Photoconductivity and Photoluminescence Studies in Copper Diffused InP
D. PAL and D.N. BOSE
Materials Science Centre, Indian Institute of Technology, Kharagpur 721302, India.

KEY WORDS Configuration coordinate diagram, copper diffusion, InP, photoconductivity, photoluminescence

Cu diffusion was carried out in p-InP at 300°C for one hour followed by 600°C for one minute. High photoconductivity (I_ph/I_d = 2.6 x 10⁵ at 200K) was observed in this sample. Information about Cu related deep levels was obtained from dark conductivity, photoconductivity and its spectral response. A Cu related photoluminescence (PL) band was observed at 1.216eV and its line-shape and line-width analysis carried out. The configuration coordinate diagram of the band was calculated and showed small lattice relaxation. In n-InP Cu diffusion at 650°C for two hours resulted in two PL bands at 1.20 and 1.01eV. The former was similar to the 1.216eV band in p-InP. The PL of the 1.01eV band was also studied in detail and the corresponding configuration coordinate diagram derived. The parameters of the Cu related bands obtained from the line-shape and line-width analysis are compared with those reported due to Mn and Fe in InP.

Donor Passivation in n-AlInAs Layers by Fluorine
Y. YAMAMOTO, N. HAYAFUJI, N. FUJII, K. KADOIWA, N. YOSHIDA, T. SONODA, and S. TAKAMIYA
Optoelectronic & Microwave Devices Laboratory, Mitsubishi Electric Corporation, 4-1, Mizuhara, Itami, Hyogo, 664, Japan.

KEY WORDS AlInAs/InGaAs/InP HEMT, donor passivation, fluorine, n-AlInAs

The mechanism of thermal degradation of both the carrier concentration and mobility in AlInAs layers due to thermally diffused fluorine is discussed. The thermal degradation occurs only in n-type AlInAs layers at temperatures as low as 350°C. In contrast, a similar thermal degradation was never observed for AlInAs containing only acceptor impurities. This phenomenon is explained by the reaction of fluorine atoms with exclusive donor impurities, which forms an ionized fluorine (anion: F^-) and results in a reduction in carrier concentration. The created F^- ions form a scattering center which leads to a reduction in carrier mobility. Experimental data support that fluorine atoms are of environmental origin and not incorporated during the growth of layers. From further comprehensive annealing studies for several kinds of (AlGaIn)As material systems, it is found that this donor passivation behavior is peculiar to those compounds which contain both AlAs and InAs.

Chemical-Bonding Structure of InP Surface in MOVPE Studied by Surface Photo-Absorption
YASUYUKI KOBAYASHI and NAOKI KOBAYASHI
NTT Basic Research Laboratories, 3-1, Morinosato Wakamiya Atsugi-Shi, Kanagawa 243-01 Japan.

KEY WORDS InP, metalorganic vapor phase epitaxy (MOVPE), phosphorus dimer, surface photo-absorption (SPA)

Using surface photo-absorption spectra, we established a phase diagram of the surface chemical-bonding structure for the P-stabilized surface in InP metalorganic vapor phase epitaxy as a function of substrate temperature and PH₃ partial pressure. At 550°C and PH₃ partial pressures of 10 and 30 Pa, the surface is (2 x 4)-like consisting of P dimers having a bond axis parallel to [ ]. As the substrate temperature decreases and the PH₃ partial pressure increases, amorphous P species start to adsorb excessively on (2x4)-like P dimer surface. A c(4 x 4)-like surface was not observed. From InP growth experiments for each P surface phase, we found that, to obtain high-quality InP epitaxial layers, excess P adsorption should be suppressed by minimizing the formation of native defects.

Raman Scattering Study of the Immiscible Region in InGaAsP Grown by LPE on (100) and (111) GaAs
TOUKO SUGIURA,¹ NOBUYASU HASE,¹ KAZUMASA HIRAMATSU,² and NOBUHIKO SAWAKI²
1--Department of Electrical Engineering, Toyota College of Technology, 2-1 Eisei-cho, Toyota-shi, Aichi 471, Japan. 2--Department of Electronics, Nagoya University, Chikusa-ku, Nagoya 464-01, Japan.

KEY WORDS Alloy semiconductor, laser Raman spectroscopy, immiscible region, InGaAsP

We have studied the asymmetric broadening of the Raman spectra of In_xGa_1-xAs_yP_1-y grown on GaAs substrates by means of the spatial correlation model. The broadening phenomena was found to be enhanced in the region of immiscibility, in agreement with PL observations. In Raman measurements, the broadening is more enhanced in the samples grown on (100) substrates than in the samples grown on (111) substrates. The enhancement is attributed to the immiscibility included in the samples grown on (100) substrate.

Degradation of PL Characteristics in Strained Layer Multi-Quantum Well Structure With Atomic Ordering Structure
NOBUYUKI OTSUKA,¹ MASAHIRO KITO,¹ YASUFUMI YABUUCHI,² MASATO ISHINO,¹ and YASUSHI MATSUI¹
1--Semiconductor Research Center, Matsushita Electric Industrial Co., Ltd. 2--Matsushita Technoresearch, Inc.; 3-1-1 Yagumonakamachi, Moriguchi, Osaka 570, Japan.

KEY WORDS InGaAsP/InP, metalorganic vapor phase epitaxy, ordering, semiconductor laser, strained layer multi-quantum well

Clarification of the degradation mechanism of photoluminescence (PL) characteristics of InGaAsP compressively strained layer multi-quantum well (SL-MQW) structures on an InP substrate is studied to realize highly strained SL-MQW lasers with a large number of well layers. An unusual temperature-dependence of the PL peak wavelength is observed in the SL-MQW structure: the shift of the PL peak wavelength is reduced with change in measurement temperature. The degradation of PL characteristics is evaluated by the reduction in the PL shift as well as an increase in PL linewidth and a decrease in PL peak intensity. The extent of the PL degradation increases with an increase in the number of well layers and an increase in strain. In the SL-MQW structure with degraded PL characteristics, the structure of CuPt-type atomic ordering is clearly observed for the first time in each barrier layer by high-resolution transmission electron microscope (HR-TEM) measurements. In the SL-MQW structure, neither dislocation nor three-dimensional nucleation is observed by TEM measurements. By increasing the growth temperature, elimination of the ordering structure as well as improvement in the PL characteristics have been confirmed even in the SL-MQW structure with a large amount of strain and a large number of well layers.

Optoelectronic Properties of Transition Metal and Rare Earth Doped Epitaxial Layers on InP for Magneto-Optics
B.J.H. STADLER,¹ K. VACCARO,¹ A. DAVIS,¹ G.O. RAMSEYER,² E.A. MARTIN,¹ H.M. DAUPLAISE,¹ L.M. THEODORE,¹ and J.P. LORENZO¹
1--USAF Rome Laboratory, Optoelectronic Components Branch, Hanscom Air Force Base, MA 01731. 2--USAF Rome Laboratory, Reliability Physics Branch, Griffiss Air Force Base, NY 13441.

KEY WORDS Faraday rotation, nGaAs, InGaAsP, InP, LPE, optoelectronic properties, rare earth, transition metal doping, waveguides

Rare earth- and transition metal-doped thin films of InP, In_0.53Ga_0.47As, and In_0.71Ga_0.29As_0.58P_0.42 were grown by liquid phase epitaxy and evaluated for use in integrated electro-optical and magneto-optical applications, such as waveguides and Faraday rotators. The films were lattice matched to (100) InP substrates, and the transition metal (Mn) and rare earth (Gd, Eu, and Er) doping concentrations were between 2.6 x 10¹⁸ and 1.5 x 10²⁰ cm^-3. The chemical profiles were generally found to be homogeneous by SIMS, although in more highly doped films the rare earths were observed to segregate toward the interfaces. The undoped films were n-type, and the net carrier concentrations in the rare earth-doped (Gd, Eu, Er) films were decreased by an order of magnitude. The Mn-doped films were p-type. Optically, the rare earth dopants were observed to raise the refractive index of the layers at 632.8 nm, and subsequent waveguiding in doped InP layers was observed at 1.3 µm. Although the Faraday rotations of our materials were much less than that of well known oxides, such as yttrium iron garnet, they were sufficient for device applications, and our materials can be much more easily integrated with InP OEIC devices. For example, a 1 cm waveguide would provide the large rotation (45°) required in isolator applications.

Thermal Stability of Interfaces Between Metals and InP-Based Materials
Y. ASHIZAWA, C. NOZAKI, T. NODA, and A. SASAKI
Toshiba Research and Development Center, 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki 210, Japan.

KEY WORDS Electrode, high-electron mobility transistor (HEMT), metal/semiconductor interface, Rutherford backscattering spectrometry, stability

The thermal stability of interfaces between metals (Ni, Pt, Ti, Mo) and III-V compound semiconductors has been investigated by the application of Rutherford backscattering spectrometry. Metal diffusion and interfacial lattice disorder of the semiconductors were analyzed for various metal/semiconductor samples annealed at temperatures up to 500°C. The interfaces of Ni/GaAs and Ti/GaAs were found to be more stable than those of Ni/In-based semiconductors and Ti/In-based semiconductors, respectively. Faster diffusion of Pt atoms was observed in In- and As-containing materials than in P-containing materials. Mo/semiconductor interfaces were the most stable.

Microstructural Analysis of the Ge/Pd(Zn) Ohmic Contact to p-InP
MOON-HO PARK,¹ L.C. WANG,¹ and D.M. HWANG²
1--Electrical Engineering Department, Mail Stop 3128, Texas A&M University, College Station, TX 77843-3128. 2--Advanced Products Research and Development Laboratory, Motorola, 3501 Ed Bluestein Blvd. Austin, TX 78721.

KEY WORDS Contact resistivity, Ge/Pd(Zn), p-III-V ohmic contact, p-ohmic interface

The interfacial microstructural analysis of the Ge/Pd(Zn) ohmic contact to p-InP, based on the solid-phase regrowth principle, is reported. Typical contact resistivities of low 10^-4 to low 10^-5 -cm² can be obtained for this contact scheme annealed at temperatures higher than 400°C. Cross-sectional transmission electron microscopy, energy dispersive x-ray composition mapping, and converge beam electron diffraction were utilized in this study for the interfacial microstructure analysis. The solid-phase regrowth process has been confirmed in this contact system on InP. Precipitates of trapped materials during solid phase regrowth have also been observed. The correlation between the electrical and microstructural properties is addressed.

Atomic Structures of Au and Ag Films Epitaxially Grown on the InP(001)-p(2 X 4) Surface
K. MORITA, K. SODA, T. KATOH, and M. HANEBUCHI
Department of Crystalline Materials Science, School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-01, Japan.

KEY WORDS Ag, atomic structure, Au, Auger electron spectroscopy (AES), InP surface, low energy electron diffraction (LEED), reflection high energy electron diffraction (RHEED), Rutherford backscattering spectroscopy(RBS), thin film

Thin films of Au and Ag deposited onto the InP(001)-p(2 x 4) surface at room temperature have been characterized by means of combined surface-layer analysis of low energy electron diffraction, reflection high energy electron diffraction, Auger electron spectroscopy, and Rutherford backscattering spectroscopy-channeling techniques. It has been found that the Au film grows epitaxially in the layer-by-layer mode along the <001> direction, while the Ag film grows in the <110> direction in the Stranski-Krastanov mode. The unit cell of a face-centered cubic lattice of the Au film is rotated azimuthally by 45° with respect to the unit cell of a zinc-blende lattice of the InP substrate. The islands of Ag(110) crystallites prefer to orient their (100) faces along the direction of the 4 times superlattice of the InP(001)-p(2 x 4) surface. The analysis of the RBS-channeling minimum yield of 1.5 MeV He⁺ ions incident along the [] direction of the InP(001) substrate shows that both the epitaxially grown Au film and Ag crystallite of less than 20Å in thickness are excellent in crystalline quality.

Characterization of Electron Traps in Plasma-Treated AlInAs
T. SUGINO,¹ D. HIRATA,¹ I. YAMAMURA,¹ K. MATSUDA,² and J. SHIRAFUJI¹
1--Department of Electrical Enginnering, Faculty of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565, Japan. 2--Horiba Ltd., Miyanohigashi, Kisshoin, Minami-ku, Kyoto 601,Japan.

KEY WORDS AlInAs, Ar plasma, electron trap, isothermal capacitance

Electron traps have been investigated for molecular beam epitaxially grown n-AlInAs by isothermal capacitance transient spectroscopy measurement. Two traps, EO1(Ec-0.44eV) and EO2(Ec-0.52eV), appear for oxygen-plasma treated samples in addition to E1(Ec-0.47eV) and E2(Ec-0.69eV) traps detected for control (as-chemically etched) sample. On the other hand, the EO1 trap is not detected for Ar plasma-treated sample. This suggests that the EO1 is generated by reaction of atomic oxygen with AlInAs and that the EO2 trap is induced by plasma damage. It is found that a reduction in the densities of the four traps occurs due to annealing subsequently after oxygen plasma treatment.

Interface Strain in InGaAs-InP Superlattices
A.R. CLAWSON¹ and C.M. HANSON²
1--University of California San Diego, ECE Dept-0407, 9500 Gilman Dr., La Jolla, CA 92093-0407. 2--NCCOSC RDTE Div 555, 49285 Bennett St., Rm 111, San Diego, CA 92152-5790.

KEY WORDS As/P replacement, InGaAs/InP superlattice, interface strain, metalorganic vapor phase epitaxy (MOVPE), x-ray diffraction (XRD)

Strain has been measured within (001) oriented OMVPE grown multilayer superlattices consisting of thin As-compound layers in InP and thin P-compound layers in GaAs. From the strain behavior, it is interpreted that As rapidly replaces P on an InP surface exposed to AsH₃ and P slowly replaces As on a As-terminated surface exposed to PH₃. This results in incorporation of an InAs-like strain in InP whose magnitude depends on the nature of the As-terminated surface. At growth temperatures above 600°C, the strain is equivalent to about one monolayer of InAs; while below 600°C, it is equivalent to two monolayers of InAs. PH₃ interaction with GaAs surfaces is sufficiently slow that GaP-like strain is observed only when deliberate interrupts under PH₃ are introduced. GaP grown on GaAs at 650°C is found to incorporate enough residual As to sustain a layer composition of GaAs_.5P_.5 over the first several monolayers.

Highly Confined Two-Dimensional Electron Gas in an In_0.52Al_0.48As/In_0.53Ga_0.47As Modulation-Doped Structure with a Strained InAs Quantum Well
TATSUSHI AKAZAKI,¹ JUNSAKU NITTA,¹ HIDEAKI TAKAYANAGI¹ TAKATOMO ENOKI,² and KUNIHIRO ARAI²
1--NTT Basic Research Laboratories. 2--NTT LSI Laboratories, 3-1 Morinosato-Wakamiya, Atsugi-shi, Kanagawa, 243-01 Japan.

KEY WORDS Effective mass, electron confinement, InAs-inserted channel, Shubnikov-de Haas measurement, strain

This paper examines a detailed analysis by Shubnikov-de Haas measurements of the effective mass of two-dimensinal electron gas (2DEG) in an In_0.52Al_0.48As/In_0.53Ga_0.47As modulation-doped (MD) structure with an InAs quantum well inserted into the InGaAs channel (InAs-inserted channel). The measured effective mass of 2DEG in the InAs-inserted-channel MD structure is in good agreement with the calculated one of the strained InAs layer on In_0.53Ga_0.47As. This indicates that almost all of the 2DEG forms in the strained InAs quantum well. These results show that the InAs-inserted-channel MD structure improves the electron confinement, since the 2DEG is confined in the InAs quantum well with the thickness of 4 nm.

REGULAR ISSUE PAPERS

KEY WORDS Double-crystal x-ray diffraction (DCXRD), heterojunction, multi-wafer-rotating-disc MOCVD, photoluminescence, shroud flow

High quality InGaN thin films and InGaN/GaN double heterojunction (DH) structures have been epitaxially grown on c-sapphire substrates by MOCVD in a production scale multi-wafer-rotating-disc reactor between 770 to 840°C. We observed that shroud flow (majority carrier gas in the reaction chamber) is the key to obtaining high quality InGaN thin films. High purity H₂ as the shroud flow results in poor crystal quality and surface morphology but strong photoluminescence (PL) at room temperature. However, pure N₂ as the shroud flow results in high crystal quality InGaN with an x-ray full width at half maximum (FWHM)_InGaN(0002) of 7.5 min and a strong room temperature PL peaking at 400 nm. In addition, InGaN/GaN single heterojunction (SH) and DH structures both have excellent surface morphology and sharp interfaces. The full width at half maximum of PL at 300K from an InGaN/GaN DH structure is about 100 meV which is the best reported to date. A high indium mole fraction in InGaN of 60% and high quality zinc doped InGaN depositions were also achieved.

A Unique, Device-Friendly Contact System for Shallow Junction p/n Indium Phosphide Devices
VICTOR G. WEIZER¹ and NAVID S. FATEMI²
1--NASA Lewis Research Center, 21000 Brookpark Rd., Cleveland, OH 44135. 2--Essential Research, Inc., 21000 Brookpark Rd., Cleveland, OH 44135.

KEY WORDS Ag/Zn/Ag metallization, InP, interdiffusion, ohmic contacts

We have discovered what appears to be a unique contact system for use on p-type InP. The new contacts provide low resistance contact to p-InP without the violent metallurgical intermixing that would normally take place between the emitter material and the contact metallization during the contact sintering process. With this new contact system, which is composed of a combination of Ag and Zn, it is possible, for the first time, to make low resistance ohmic contact directly to a shallow junction p/n InP device without destroying the device while doing so. Specific contact resistivity values in the low 10^-4-cm² range are readily achieved. After a description of the new system, we suggest possible mechanisms to explain the observed behavior.

Effect of the Post-As⁺-Implantation Thermal Treatment on MBE HgCdTe Optical Properties
S.P. GUO, Y. CHANG, J.M. ZHANG, X.C. SHEN, J.H. CHU, and S.X. YUAN
Shanghai Institute of Technical Physics, Chinese Academy of Sciences, 420 Zhong Shan Bei Yi Road, Shanghai 200083, China.

KEY WORDS HgCdTe, ion-implantation, MBE, thermal treatment

HgCdTe epilayers were grown by molecular beam epitaxy. A series of As⁺-implanted CdTe and HgCdTe epilayers annealed under different temperatures were investigated by photoluminescence spectroscopy. More As⁺ ions can occupy the Te sublattice after the samples were annealed at 450°C, and the acceptor level of As⁺ on the Te sublattice for HgCdTe material (x0.39) is 31.5 meV. The Raman spectrum study indicates a recovery of the crystalline perfection after the post-As⁺-implantation thermal treatment.

Magnetron Sputtered Transparent Conducting CdO Thin Films
K. GURUMURUGAN, D. MANGALARAJ, and SA.K. NARAYANDASS
Thin Film Laboratory, Department of Physics, Bharathiar University, Coimbatore 641 046, India.

KEY WORDS Cadmium oxide, sputtering, structure

Thin films of cadmium oxide have been produced by dc reactive magnetron sputtering in nitrogen and oxygen atmosphere. The structural, optical, and electrical characterization of these films are investigated. Structural analysis indicates that the films are polycrystalline and cubic. Composition analysis by Rutherford backscattering spectrometry has been made and it is found that the films contain excess cadmium and deficient oxygen. It is observed from the optical properties that the films possess a transmittance of about 85% in the visible and near infrared regions of the spectrum and direct bandgap values in the range 2.50 to 2.68 eV for films of thicknesses 146 to 177 nm. Electrical measurements point out that the films have resistivity, carrier concentration, and mobility in the range 2.65 to 6.64 X 10^-6m, 1.60 to 2.35 X 10²⁶ m^-3, and 57.65 to 100.48 X 10^-4 m² v^-1 s^-1, respectively.

LETTERS SECTION

KEY WORDS AlGaAs, aluminum precursor, organometallic vapor phase epitaxy (OMVPE), tritertiarybutylaluminum

High-quality AlGaAs epilayers have been grown by low pressure organometallic vapor phase epitaxy with a new aluminum precursor tritertiarybutylaluminum (TTBAl). Layers grown at 650°C have a featureless mirror surface morphology and strong room temperature photoluminescence. Carbon was not detectable in chemical analysis by secondary ion mass spectroscopy, nor in low temperature (4K) photoluminescence spectra. Oxygen concentration in Al_0.25Ga_0.75As is as low as ~2-3 X 10¹⁷ cm^-3. Nominally undoped AlGaAs layers exhibit n-type conductivity with electron concentrations at ~1-1.5 X 10¹⁶ cm^-3. A high degree of compositional uniformity over 5 cm diam substrates (0.268 +/- 0.001) was obtained. These results indicate the potential for TTBAl as an aluminum precursor for low temperature growth of Al-containing III-V alloys.