JOURNAL OF ELECTRONIC MATERIALS
	ABSTRACTS Volume 26, Number 1, January 1997 This Month Featuring: Regular Issue Papers. View January 1997 Table of Contents.

REGULAR ISSUE PAPERS

KEY WORDS GaN, lattice mismatch, metalorganic chemical vapor deposition (MOCVD), thermal cycle annealing

The effect of in-situ thermal cycle annealing (TCA) has been investigated for GaN growth on GaAs(100), GaAs(111) and sapphire substrates. X-ray diffractometry (XRD) and surface morphology studies were performed for this purpose. Enhanced cubic phase characteristics were observed by employing annealing for GaN layers grown on (001) GaAs. The thickness of the layer subject to annealing is critical in determining the phase of the subsequently grown layer. Thin initial layers appear to permit maintenance of the cubic phase characteristics shown by the substrate, while hexagonal phase characteristics are manifestedfor thick initial layers. Higher temperature of annealing of thick pre-annealed layers results in changes from mixed cubic/hexagonal phase to pure hexagonal phase. Growth on GaAs(111) substrates showed single cubic phase characteristics and similar enhancement of crystal quality by using TCA as for layers on GaAs(001). Micro-cracks were found to be present after TCA on GaAs(111) substrates. Thermal cycling also appears to be beneficial for layers grown on sapphire substrates.

Zn-Doped InGaP Grown by the LP-MOCVD
R. KÚDELA, J. NOVÁK, and M. KUERA
Institute of Electrical Engineering, Slovak Academy of Sciences, 842 39 Bratislava, Slovak Republic.

KEY WORDS InGaP, low pressure metalorganic chemical vapor deposition (LP-MOCVD), Zn-doping

Zn-doped In_0.485Ga_0.515P epitaxial layers were grown on semi-insulating GaAs substrates by low pressure metalorganic chemical vapor deposition (LP-MOCVD) at the temperatures 520, 560, and 720°C. Growth conditions were optimized with respect to surface morphology for each growth temperature and the growth rates were in the range from 0.6 to 1.4 µm/h. Diethylzinc was used as a Zn precursor and the dependencies of hole concentrations, mobilities, and photoluminescence spectra on the growth conditions were studied. Doping levels from 3 x 10¹⁷ to 3 x 10¹⁸ cm^-3 were obtained at different growth temperatures. The highest hole mobilities were measured in the layers grown at 560°C. The acceptor activation energy of 21 meV was measured from the photoluminesce spectra in our samples. As the results are not directly comparable with the data from the literature, theoretical models of Zn incorporation are discussed. A desorption energy of 0.55 eV of Zn atoms was calculated from the temperature dependence of the zinc distribution coefficient K_Zn.

A Mössbauer Study of Tin-Based Intermetallics Formed During the Manufacture of Dispersion-Strengthened Composite Solders
ROBERT C. RENO,¹ MICHAEL J. PANUNTO,¹ and BRETT H. PIEKARSKI²
1--Department of Physics, University of Maryland Baltimore County, Catonsville, MD 21228. 2--U.S. Army Research Laboratory, 2800 Powder Mill Road, Adelphi, MD 20783.

KEY WORDS Dispersion strengthening, intermetallics, Mössbauer spectroscopy, solder

Mössbauer spectroscopy was used to characterize dispersion-strengthened composite solder powders that were formed through hot gas spray atomization. To perform quantitative measurements, we first measured the relative recoilless fractions of eutectic solder and three intermetallic compounds: Cu₃Sn, Cu₆Sn₅, and Ni₃Sn₄. These results were then used to determine the concentrations of intermetallic species present in various composite solder samples. Mössbauer spectroscopy was shown to be an effective tool in the analysis of dispersion-strengthened composite solders and was preferentially sensitive to the presence of tin-based intermetallics and oxides.

Beryllium Ion Implantation into GaAs and Pseudomorphic AlGaAs/InGaAs/GaAs Heterostructure
J.F. THIERY,¹ H. FAWAZ,¹ J.C. PESANT,¹ N.T. LINH,² and G. SALMER¹
1--Institut d'Electronique et de Microélectronique du Nord, Avenue Poincaré, 59652 Villeneuve d'Ascq, France. 2--Picogiga, 5, rue de la Réunion. Z.A. de Courteboeuf, 91940 les Ulis, France.

KEY WORDS Beryllium, GaAs, heterostructure insulated-gate field-effect transistor (HIGFET), implantation, rapid thermal annealing (RTA)

Implantations of Be, Be + P, Be + F, Be + P +F, BeF and Mg + P into GaAs and AlGaAs/InGaAs/GaAs pseudomorphic heterostructure were evaluated by secondary ion mass spectrometry profilings and electrical resistivity measurements. Rapid thermal annealing causes a strong diffusion of Be when implanted alone. Co-implantation with P prevents both diffusion and degradation of the Gaussian-shape implant distribution and thus improves the semiconductor sheet resistivity. Annealing at 850° for 10 s for a Be + P co-implant results in a 60% activation efficiency, and lower diffusion and resistivity when compared to single Be, Be + F, Be + F + P, BeF, and Mg + P implanted at the same dose.

Optical Properties and Reactive Sputtering Conditions of AIN and AlSiN Thin Films for Magneto-Optical Applications
X.S. MIAO,¹ Y.C. CHAN,¹ and Z.Y. LEE²
1--Department of Electronic Engineering, City University of Hong Kong, Hong Kong. 2--Department of Solid State Electronics, Huazhong University of Science and Technology, Wuhan 430074, China.

KEY WORDS AlN film, AlSiN film, Kerr effect enhancement, reactive sputtering

The dependence of the refractive index and film thickness of AlN and AlSiN thin films on the reactive sputtering conditions (N₂ partial pressure, total pressure, and rf sputtering power) have been studied in detail and analyzed in terms of the mechanism of reactive sputtering and the target poisoning phenomenon. On the basis of the results, the sputtering conditions of AlN and AlSiN films have been optimized for magneto-optical applications. The AlN and AlSiN films after optimization of the sputtering conditions had very high transmissivity and refractive index, and were suitable for magneto-optical Kerr effect enhancement. A marked enhancement of the magneto-optical Kerr effect for a TbFeCo film coated with AlN and AlSiN films was observed. The improvement of the signal-to-noise ratio obtained with the AlSiN film was greater than the AlN film.

Anomalous Lateral Zn Surface Diffusion in InP Caused by Zn-Contained Metallization
MOON-HO PARK, P.H. HAO, and L.C. WANG
Electrical Engineering Department, Texas A&M University, College Station, TX 77843-3128.

KEY WORDS InP, Pd/Zn/Pd contact, Zn surface diffusion

We report an anomalous Zn surface diffusion in InP during annealing of ohmic contact structures containing Zn. A Pd/Zn/Pd contact was used to demonstrate this phenomenon. Electrical properties of the contact were monitored to corroborate this anomalous surface diffusion. Cross-sectional scanning electron microscopy was also used to delineate the Zn diffusion front lines. It was found that the Zn surface lateral diffusion can extend 50 µm for samples annealed at 500°C or higher temperatures. Close attention should be paid to this anomalous lateral surface diffusion during fabrication of devices using Zn-contained ohmic contacts.

Subnanometer Analysis and Modeling of MBE Grown InP Based MODFETs
MATTHEW SEAFORD,^1,3 SCOTT MASSIE,³ DAVE HARTZELL,³ GLENN MARTIN,^2,4 WARREN WU,⁵JOHN TUCKER,⁵ and LESTER EASTMAN²
1--Cornell University, Ithaca, NY 14853. Current address: Materials Directorate, Wright Laboratory, WPAFB, OH 45433. 2--Cornell University, Ithaca, NY 14853. 3--Quantum Epitaxial Designs, Bethlehem, PA 18062. 4--Geo-Centers, Inc., Eatontown, NJ 07724. 5--University of Illinois at Urbana-Champaign, Urbana, IL 61801.

KEY WORDS Clustering, cross-sectional scanning tunneling microscopy (XSTM), InGaAs/InAlAs, modulation-doped field-effect transistors (MODFETs), molecular beam epitaxy (MBE), sheet charge

InGaAs/InAlAs double-doped double-strained modulation-doped field-effect transistors (3D-SMODFETs)¹ were grown by solid source molecular beam epitaxy. The structures were characterized using high resolution x-ray diffraction, Hall effect, and cross-sectional scanning tunneling microscopy. A record two-dimensional electron gas (2DEG) sheet density of 8.5 x 10¹²/cm² and 8.1 x 10¹²/cm² for 300 and 77K, respectively, was achieved. The mobility was 6500 and 12000 cm²/Vs for 300 and 77K, respectively. To the author's knowledge,² the previous record 2DEG result was 6.58 x 10¹²/cm². The electron mobility was limited by alloy scattering and interface roughness caused by the presence of "clustering." Using cross-sectional scanning tunneling microscopy to verify the presence of these clusters, we have the first images of the lattice matched InAlAs (spacer)-InGaAs (quantum well) interface. These images reveal clusters that have approximate spherical or cylindrical shapes with equivalent cubic dimensions ranging from 25 to 45Å.

Effect of SiO₂ Powder on Mirror Polishing of InP Wafers
YUJI MORISAWA,¹ ISAO KIKUMA,¹ NAOKI TAKAYAMA,² and MANABU TAKEUCHI²
1--Department of Electrical and Electronic Engineering, Ibaraki University, 4-12-1 Nakanarusawa, Hitachi, 316 Japan. 2--Nihon Exceed Corporation, 4382-4 Uchimoriya, Mitsukaido, Ibaraki, 303 Japan.

KEY WORDS InP wafers, mechanical-chemical polishing

This paper describes a mechanical-chemical polishing technique of InP wafers using NaOCl, citric acid, and SiO₂ powder solutions. The polishing rate rapidly increases by adding SiO₂ powder to NaOCl and citric acid solutions. We study the dependence of the polishing rate on SiO₂ powder and discuss the mechanical-chemical effect of the mirror polishing of InP wafers with NaOCl, citric acid, and SiO₂ powder solutions. We observe an increase in the polishing rate of InP wafers from 0.2 to 0.9 µm/min when SiO₂ powder is added to NaOCl and citric acid solutions.

Tertiarybutylarsine for Metalorganic Chemical Vapor Deposition Growth of High Purity, High Uniformity Films
H.C. CHUI,¹ R.M. BIEFELD,² B.E. HAMMONS,² W.G. BREILAND,² T.M. BRENNAN,² E.D. JONES,² H.K. MOFFAT,² M.H. KIM,³ P. GRODZINSKI,³ K.H. CHANG,³ and H.C. LEE³
1--Sandia National Laboratories, Albuquerque, NM 87185-0603. Present address: Hewlett-Packard, 370 West Trimble Raod, MS 91ML, San Jose, CA 95131. 2--Sandia National Laboratories, Albuquerque, NM 87185-0603. 3--Phoenix Corporate Research Laboratories, Motorola Inc., Tempe, AZ 85284.

KEY WORDS AlGaAs, GaAs, InGaAs, low p-type carrier concentration, tertiarybutylarsine (TBA)

We have performed an extensive study of GaAs, Al_0.22Ga_0.78As, and In_0.16Ga_0.84As grown using tertiarybutylarsine (TBA) in an ultra-high purity metalorganic chemical vapor deposition multi-wafer reactor. Key results include: high purity TBA AlGaAs layers with the lowest p-type carrier concentrations (4 x 10¹⁴ cm^-3) reported to date; 4K photoluminescence bound exciton linewidths as narrow as 4.3 meV; C, O. Si, and S concentrations below the secondary ion mass spectrometry detection limit; and InGaAs/GaAs quantum wells with 20K PL linewidths as narrow as 3.5 meV. We also observe a strong dependence of growth rates and doping efficiency on group-V partial pressure, possibly due to a competition between excess group-V species and group-III or Si species for group-III surface sites. Finally, we demonstrate record uniformity using TBA with an AlGaAs thickness variation of only ±1.4% across a 4 inch wafer.

Effects of Rapid Thermal Annealing on the Device Characteristics of Quantum Well Infrared Photodetectors
D.K. SENGUPTA,¹ W. FANG,¹ J.I. MALIN,¹ A.P. CURTIS,¹ T. HORTON,¹ H.C. KUO,¹ D. TURNBULL,¹ C.H. LIN,¹ J. LI,¹ K.C. HSIEH,¹ S.L. CHUANG,¹ I. ADESIDA,¹ M. FENG,¹ S.G. BISHOP,¹ G.E. STILLMAN,¹ J.M. GIBSON,² H. CHEN,² J. MAZUMDER,² and H.C. LIU³
1--Department of Electrical and Computer Engineering, Center for Compound Semiconductor Microelectronics, University of Illinois at Urbana-Champaign, Urbana, IL 61801. 2--Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801. 3--Institute for Microstructural Sciences, National Research Council, Canada K1A 0R6.

KEY WORDS Dark current characteristics, multiple quantum well infrared photodectors (QWIPs), quantum efficiency, rapid thermal annealing (RTA), red shift

The effect of rapid thermal annealing (RTA) on important detector characteristics such as dark current, absolute response, noise, and detectivity is investigated for quantum-well infrared photodetectors (QWIP) operating in the 8-12 µm wavelength regime. A comprehensive set of experiments is conducted on QWIPs fabricated from both as-grown and annealed multiple-quantum-well structures. RTA is done at an anneal temperature of 850°C for 30 s using an SiO₂ encapsulant. In general, a decrease in performance is observed for RTA QWIPs when compared to the as-grown detectors. The peak absolute response of the annealed QWIPs is lower by almost a factor of four, which results in a factor of four decrease in quantum efficiency. In addition, a degraded noise performance results in a detectivity which is five times lower than that of QWIPs using as-grown structures. Theoretical calculations of the absorption coefficient spectrum are in excellent agreement with the experimental data.