JOURNAL OF ELECTRONIC MATERIALS
	ABSTRACTS Volume 24, Number 1, January 1995 This Month Featuring: Regular Issue Papers. View January 1995 Table of Contents.

REGULAR ISSUE PAPERS

KEY WORDS CCl4, GaAs:C, molecular beam epitaxy

CCl₄ has been used as a carbon acceptor dopant source for GaAs grown by elemental source molecular beam epitaxy. Deposition of CCl₄ during normal arsenic stabilized growth of GaAs resulted in low mobility, p-type material. Attempts to thermally crack the CCl₄ using a heated gas cracking source resulted in an even lower hole concentration and mobility. One possible explanation for this ineffective acceptor doping behavior, relative to growth environments containing hydrogen (metalorganic chemical vapor deposition) where CCl₄ is an effective dopant, is that hydrogen plays a role in the incorporation of the carbon. Another possible explanation for the poor doping behavior is that the CCl₄ was being modified by the gas cracker, even at relatively low gas cracker temperatures. Further experimentation with different injection schemes will be necessary to better understand the doping behavior. Depositing the CCl₄ onto static, gallium-rich surfaces produces GaAs:C with hole mobilities comparable to GaAs:Be. Average hole concentrations as high as 4 x 10¹⁹ have been demonstrated. Carbon doped AlGaAs/GaAs heterojunction bipolor transistors (BTs) have been fabricated with the same characteristics as Be doped HBTs grown in the same MBE system.

Crystallographic Orientation Dependence of the Growth Rate for GaAs Low Pressure Organometallic Vapor Phase Epitaxy
S.H. JONES, L.S. SALINAS, J.R. JONES, and K. MAYER
Applied Electrophysics Laboratory, Department of Electrical Engineering, University of Virginia, Charlottesville, VA 22903-2442.

KEY WORDS GaAs, growth modeling, organometallic vapor phase epitaxy (OMVPE)

The complete crystallographic orientation dependence of the growth rate for GaAs low pressure organometallic vapor phase epitaxy (LPOMVPE) is determined using a previously described semi-empirical model. A set of LPOMVPE growth rate polar diagrams is presented for reactor temperatures near 550°C as well as near 700°C. Also, the variation of the growth rate polar diagrams as a function of process variables is given. The experimental data utilized in the semiempirical model was attained using a typical horizontal reactor LPOMVPE system and typical LPOMVPE process parameters.

Electron Irradiation Induced Defects and Schottky Diode Characteristics for Metalorganic Vapor Phase Epitaxy and Molecular Beam Epitaxial n-GaAs
G.H. YOUSEFI,¹ J.B. WEBB,¹ R. ROUSINA,² and S.M. KHANNA³
1--Institute for Microstructural Sciences, National Research Council Canada, M-50 Montreal Road, Ottawa, Ontario K1A OR6 Canada. 2--Bell Northern Research Ltd., P.O. Box 3511, Station C, Ottawa, Ontario K1Y 4H7 Canada.3--Defence Research Establishment Ottawa, Ottawa, Ontario K1A 0Z4 Canada.

KEY WORDS Deep level transient spectroscopy ( DLTS), defects, electron irradiation, GaAs, metalorganic vapor phase epitaxy (MOVPE), molecular beam epitaxy (MBE)

A considerable body of information is available in the literature concerning the effects of high energy electron irradiation on the formation of deep trapping levels in GaAs. Most of these studies have dealt with bulk material or material grown by vapor phase epitaxy (VPE). However, whether these studies are representative of GaAs epilayers grown by metalorganic vapor phase epitaxy (MOVPE) or molecular beam epitaxy is not clear, particularly when the gallium and arsenic species used in the growth and hence optimal conditions for growth, differ widely between techniques. In fact, the results reported in this study show significant differences in the behavior of material produced by these techniques. Deep level transient spectroscopy (DLTS) is used in this work to characterize the deep electron traps formed during 7 MeV electron irradiation. In addition, the current voltage characteristics of the Schottky diodes used in the DLTS studies have been evaluated before and after irradiation to ascertain the effects of irradiation on device performance. It has been found that an additional trapping level is produced in MOVPE-grown material of high background doping and that the carrier removal in this material is not a simple function related to increased electron fluence as observed in previous studies on VPE material.

Evidence of a Thermally Stable Carbon-Nitrogen Deep Level in Carbon-Doped, Nitrogen-lmplanted, GaAs and AlGaAs
J.C. ZOLPER, M.E. SHERWIN, A.G. BACA, and R. P. SCHNEIDER, JR.
Sandia National Laboratories, Albuquerque NM 87185-5800.

KEY WORDS AlGaAs, carbon, GaAs, implantation isolation, nitrogen

Nitrogen ion implantation is shown to form high resistivity regions (_s 1 x 10¹⁰ /square) in C-doped GaAs and Al_0.35Ga_0.65As that remains compensated after a 900°C anneal. This is in contrast to oxygen or fluorine implantation in C-doped GaAs which both recover the initial conductivity after a aufficiently high temperature anneal (800°C for F and 900°C for O). In C-doped Al_0.35Ga_0.65As N- and O-implant isolation is thermally stable but F-implanted samples regain the initial conductivity after a 700°C anneal. A dose dependence is observed for the formation of thermally stable N-implant compensation for both the GaAs and AlGaAs samples. A C-N complex is suggested as the source of the compensating defect level for the N-implanted samples. Sheet resistance data vs anneal temperature and estimates of the depth ofthe defect levels are reported. This result will have application to heterojunction bipolar transistors and complementary heterostructure field effect transistor technologies that employ C-doped AlGaAs or GaAs layers along with high temperature post-implant isolation processing.

Growth of GaAs by Vacuum Atomic Layer Epitaxy Using Tertiarybutylarsine
MING Y. JOW, BANG Y. MAA, TAKASHI MORISHITA,* and P. DANIEL DAPKUS
Department of Materials Science and Electrical Engineering, University of Southern California, Los Angeles, CA 90089. *Central Laboratory, ASAHI Chemical Industry Co. Ltd., 2-1 Samajima, Fuji City, Sizuoka, 416 Japan.

KEY WORDS Atomic layer epitaxy, GaAs, tertiarybutylarsine

We report the results of GaAs grown by vacuum atomic layer epitaxy using trimethylgallium (TMGa) and tertiarybutylarsine (TBAs) as the group III and V sources. The growth rate saturates at one monolayer per cycle for a wide range of growth parameters. The temperature window for monolayer growth is as wide as 70°C. All the films are p-type with the carrier concentration depending on the exposure conditions of TMGa and TBAs.

A Study of the Transition from High to Low Resistivity in As-Grown GaAs MBE Material
C.E. STUTZ,¹ D.C. LOOK,² E.N. TAYLOR,¹ J.R. SIZELOVE,¹ and P.W. YU²
1--WL/ELR Bldg 620, 2241 Avionics Circle Ste. 21, Wright-Patterson AFB, OH 45433-7323. 2--University Research Center, Wright State University, Dayton, OH 45435.

KEY WORDS GaAs, low-temperature grown GaAs, molecular beam epitaxy (MBE)

This work discusses the transition from high resistivity as-grown GaAs layers to thermally metastable low resistivity as-grown layers by molecular beam epitaxy. This transition occurs at about 430°C and coincides with a reflective high energy electron diffraction reconstruction change from a 2 x 1 to 2 x 4 pattern for an As₄/Ga beam equivalent pressure ratio of 20. For growth temperatures in the range 350 to 430°C, room temperature Hall-effect measurements have shown resistivities of >10⁷ ohm-cm and photoluminescence has shown new peaks at 0.747 eV and a band from 0.708 to 0.716 eV at 4.2K, in unannealed material.

Low Resistance Pd/Ge Ohmic Contacts to Epitaxially Lifted-Off n-type GaAs Film
H. FATHOLLAHNEJAD, R. RAJESH,* J. LIU,* R. DROOPAD, G.N. MARACAS, and R.W. CARPENTER*
Department of Electrical Engineering, Center for Solid State Electronics Research, Arizona State University, Tempe, AZ 85287-6206. *Center for Solid State Science, Arizona State University, Tempe AZ 85287-1704.

KEY WORDS Epitaxial lift-off (ELO) method, n-type GaAs, Pd/Ge ohmic contacts

A low resistance PdGe nonalloyed ohmic contact has been successfully formed to epitaxially lifted-off n-type GaAs films. The contact is made by lifting off partially metallized n-type GaAs films using the epitaxial lift-off method and bonding them to metallized Si substrates by natural intermolecular Van Der Waals forces. Low temperature sintering (200°C) of this contact results in metallurgical bonding and formation of the ohmic contact. We have measured specific contact resistances of 5 x 10^-5 -cm² which is almost half the value obtained for pure Pd contacts. Germanium forms a degenerately doped heterojunction interfacial layer to GaAs. Our experimental results show that germanium diffuses to the interface and acts as a dopant layer to n-GaAs film surface. Therefore, for epitaxially lifted-off n-type GaAs films, PdGe is a low resistance ohmic metal contact to use.

Solder Joint Reliability of Indium-Alloy Interconnection
KOZO SHIMIZU, TERU NAKANISHI, KAZUAKI KARASAWA, KAORU HASHIMOTO, and KOICHI NIWA
Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi 243-01, Japan.

KEY WORDS Fatigue, flip-chip, In alloys, interconnection, solder

Recent high-density very large scale integrated (VLSI) interconnections in multichip modules require high-reliability solder interconnection to enable us to achieve small interconnect size and large number of input/output terminals, and to minimize soft errors in VLSIs induced by a-particle emission from solder. Lead-free solders such as indium (In)-alloy solders are a possible alternative to conventional lead-tin (Pb-Sn) solders. To realize reliable interconnections using In-alloy solders, fatigue behavior, finite element method (FEM) simulations, and dissolution and reaction between solder and metallization were studied with flip-chip interconnection models. We measured the fatigue life of solder joints and the mechanical properties of solders, and compared the results with a computer simulation based on the FEM. Indium-alloy solders have better mechanical properties for solder joints, and their flip-chip interconnection models showed a longer fatigue life than that of Pb-Sn solder in thermal shock tests between liquid nitrogen and room temperatures. The fatigue characteristics obtained by experiment agree with that given by FEM analysis. Dissolution tests show that Pt film is resistant to dissolution into In solder, indicating that Pt is an adequate barrier layer material for In solder. This test also shows that Au dissolution into the In-Sn solder raises its melting point; however, Ag addition to In-Sn solder prevents melting point rise. Experimental results show that In-alloy solders are suitable for fabricating reliable interconnections.

Improving the Electrical Conductivity of Composites Comprised of Short Conducting Fibers in a Nonconducting Matrix: The Addition of a Nonconducting Particulate Filler
PU-WOEI CHEN and D.D.L. CHUNG
Composite Materials Research Laboratory, Furnas Hall, State University of New York at Buffalo, Buffalo, NY 14260-4400.

KEY WORDS Carbon fibers, conducting composite, electrical conductivity

The addition of a second discontinuous filler (silica fume) that is essentially nonconducting to a composite with a comparably nonconducting matrix (cement) and a conducting discontinuous filler (carbon fibers) was found to increase the electrical conductivity of the composite when the conducting filler volume fraction was less than 3.2%. The maximum conducting filler volume fraction for the second filler to be effective was only 0.5% when the second filler was sand, which was much coarser than silica fume. The improved conductivity due to the presence of the second filler is due to the improved dispersion of the conducting filler. The silica fume addition did not affect the percolation threshold, but the sand addition increased the threshold.

Surface Reaction and Stability of Parylene N and F Thin Films at Elevated Temperatures
P.K. WU,* G.-R. YANG,² J.F. MCDONALD,³ and T.-M. LU³
1--Center for Integrated Electronics, Rensselaer Polytechnic Institute, Troy, NY 12180. 2--Department of Physics, 3--Electrical, Computer, and System Engineering Department. *Present address: Department of Physics, Southern Oregon State College, Ashland, OR 97520.

KEY WORDS Diffusion, parylene, surfaces, thin films

The morphology and chemical structure of Parylene F and Parylene N films annealed in air, N₂, and vacuum were examined. The decomposition temperatures of Parylene N in air, N₂, and vacuum were determined to be 175, 350, and 425°C, respectively. The decomposition temperatures of Parylene F in air and N₂ were determined to be 400 and 500°C, respectively. For both materials, the decomposition process with and without the presence of O is different. In the case of Parylene N, O diffuses into the materials and reacts with the C in the polymer. In the case of Parylene F, no reaction products with O are observed on the surface. Annealing at the decomposition temperature resulted in the decomposition of -CF₂- functional groups to -CF- functional groups in the Parylene F. Thicker films, >1 µm, of either material cracked during annealing while films <0.5 µm, remained smooth and transparent. Pinholes were also observed in the Parylene F film deposited using the Gorham method after annealing.

Electrical and Optical Characterization of Mg, Mg/P, and Mg/Ar Implants into InP:Fe
JAIME M. MARTIN,¹ S. GARCÍA,¹ F. CALLE,² I. MÁRTIL,¹ and G. GONZÁLEZ-DÍAZ¹
Departamento de Electricidad y Electronica, Facultad de Fisicas, Universidad Complutense, Ciudad Universitaria, 28040 Madrid, Spain. 2--Departamento de Ingenieria Electronica. ETSI Telecomunicacion, Universidad Politecnica, 28040 Madrid, Spain.

KEY WORDS Diffusion, implantation, photoluminescence, rapid thermal annealing (RTA)

Mg, Mg/P, and Mg/Ar implantations were performed into InP:Fe with an energy of 80 keV for obtaining shallow p⁺ layers suitable for device applications. After rapid thermal annealing at 850 or 875°C for 5 or 10 s, activations between 10 and 50% and mobilities as high as 110 cm²/Vs were obtained for the different doses employed. For the implantations with 10¹⁴ cm^-2, differential Hall measurements showed hole profiles with peak concentrations in the mid-10¹⁸ cm^-3 range and Hall mobilities of 90 cm²/Vs. However, secondary ion mass spectrometry profiles showed a clear pileup of Mg at the surface and in-diffusion tails deeper than 2 µm. Phosphorus or Ar co-implantation reduced the Mg in-diffusion and increased the activation, but not as clearly as in the case of Be implants. Photoluminescence (PL) measurements demonstrated the good crystalline quality of the material after all the annealing cycles employed. In the photoluminescence spectra, together with narrow emissions close to the gap wavelength, two broad bands, centered at about 1.3 and 0.87 eV were found, this last being the dominant emission of the PL spectra from the layers with higher implanted doses. The origin of this band is tentatively assigned to complexes involving Mg and a defect.