JOURNAL OF ELECTRONIC MATERIALS
	ABSTRACTS Volume 24, Number 6, June 1995 This Month Featuring: Regular Issue Papers. View June 1995 Table of Contents.

REGULAR ISSUE PAPERS

KEY WORDS GaAsP/GaAs, heterojunction band offsets, strain effects

Valence band offsets at [100]-oriented heterojunctions between tensile-strained GaAs_1-xP_x and unstrained GaAs are studied experimentally and theoretically. Light-hole (LH) and heavy-hole (HH) offsets are first extracted from the well-width dependence of valence subband splittings observed in luminescence spectra of tensile-strained GaAs_1-xP_x/GaAs quantum wells of various compositions (x = 0.06, 0.09, and 0.19). This data is then combined with results from two other laboratories, yielding a set of 30 independent experimental offset values for junctions with compositions throughout the range 0.06x 0.32. The data are found to be highly consistent, with linear fits E_LH = -140x (meV) and E_HH=
-401x (meV) describing the measured offsets to within less than 5 meV on average. Experimental results are then compared with theoretical predictions for the GaAs_1-xP_x/GaAs system obtained from a tight-binding model for strained heterojunctions. Predictions from the tight-binding calculations are found to lie within experimental scatter for the LH offsets, which define the valence band edge in these heterostructures, while magnitudes of the tight-binding HH offsets exceed measured values by ~20% on average.

Deposition and Characterization of Indium Oxide and Indium Tin Oxide Semiconducting Thin Films by Reactive Thermal Deposition Technique
P. THILAKAN, S. KALAINATHAN, J. KUMAR, and P. RAMASAMY
Crystal Growth Centre, Anna University, Madras - 25, India.

KEY WORDS Indium oxide, indium-tin alloy, indium-tin oxide, quartz substrates, reactive thermal deposition, thin film

In this paper, the deposition conditions and the characterization properties of the indium oxide (IO) and indium tin oxide (ITO) thin films deposited by a reactive thermal deposition technique using the indium, indium-tin alloy sources are reported. The actively involved parameters during deposition have been identified for various substrate temperatures. The effect of oxygen partial pressure in evaporation has been identified. The indium-tin alloy source which was used in this work was prepared by hot zone diffusion technique. The structural, optical, and electrical properties have been characterized using optical microscope, x-ray diffractometer, ultraviolet spectrophotometer, and Hall effect measurement setup. The uniformity of the deposited films and the uniformity of the substrate surface effect on the deposited thin films were analyzed through sheet resistance measurements. The depositions were carried out on glass and quartz substrates. Good optical transmittance (99%) was achieved for 740 nm wavelength and above. The absorbance spectrum exhibit a value of 2% absorbance for IO/quartz structures. Large area (5.0 x 3.8 cm) film with unique optical properties is also reported here.

Growth Pressure Effects on Si/Si_1-xGe_x Chemical Vapor Deposition
. MATUTINOVIC-KRSTELJ,^1,2 E. CHASON,^1,3 and J.C. STURM¹
1--Department of Electrical Engineering, Princeton University, Princeton, NJ 08544. 2--Present address: McKinsey & Company, 55 E. 52nd Street, New York, NY 10022. 3--Sandia National Laboratories, Albuquerque, NM 87185.

KEY WORDS Growth pressure effects, rapid thermal chemical deposition, Si/SiGe

We studied the effects of growth pressure on Si_1-xGe_x/Si heterostructures grown by rapid thermal chemical vapor deposition in the pressure range of 6-220 Torr. The material was characterized by photoluminescence (PL), x-ray reflectivity, and electrical measurements on resonant tunneling diodes (RTDs). High quality material was demonstrated throughout the pressure range, but a weaker PL intensity at higher pressure (220 Torr) indicates lower lifetimes. Interface abruptness was degraded at higher pressures due to gas transients. This was confirmed by x-ray reflectivity measurements and the performance of RTDs. We have established a low pressure limit to interface roughness of 0.2-0.5 nm, determined by x-ray reflectivity.

Pyrolysis of Tertiarybutylphosphine at Low Pressure
C.W. HILL, G.B. STRINGFELLOW, and L.P. SADWICK
Departments of Materials Science and Engineering and Electrical Engineering, University of Utah, Salt Lake City, UT 84112.

KEY WORDS Chemical beam epitaxy (CBE), low pressure, pyrolysis, tertiarybutylphosphine cracking

The pyrolysis of tertiarybutylphosphine (TBP) has been studied in the low pressure conditions used for chemical beam epitaxy (CBE). The pyrolysis studies were carried out in low pressure reactors of two different configurations, one of which is a cracker cell designed for use in a CBE system. The reaction products were studied using a quadrupole mass spectrometer. The products observed are accounted for by a reaction mechanism involving homolysis of the parent TBP molecule to produce PH₂ and C₄H₉ radicals. These undergo subsequent reactions to form the stable products C₄H₈, PH_3, and H₂, with smaller amounts of P and P₂ being produced. The production of the sub-hydride PH₂ using this cracker cell design indicates that the use of partially cracked TBP may be a promising technique for reducing the amount of carbon incorporated into the growing epitaxial layer.

Defect Formation in Epitaxial Oxide Dielectric Layers Due to Substrate Surface Relief
P.C. MC INTYRE, B.P. CHANG, N. SONNENBERG, and M.J. CIMA
Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02319.

KEY WORDS CeO2 films, defects, LaAlO3 substrates

Defects were characterized in epitaxial (001) CeO₂ films deposited and planarized in situ on patterned (001) LaAlO₃ substrates by ion beam assisted deposition (IBAD). A hill and valley structure with steps running parallel to the [100] LaAlO₃ axis was produced on the surface of the substrate by photolithography and ion beam etching prior to film deposition. A conformal epitaxial CeO₂ layer of ~100 nm thickness was deposited on the heated substrate by e-beam evaporation. Lattice-matching between the e-beam film and the substrate was of the type: (001) CeO₂||(001) LaAlO₃ and [110] CeO₂||[100] LaAlO₃. Evaporative deposition of additional film onto the conformal layer was accompanied by bombardment with a 500 eV argon/oxygen ion beam to promote in situ planarization. Extreme lattice misfit for the orientation (001) CeO₂||(001) LaAlO₃ and [001] CeO₂||[001] LaAlO₃ caused formation of dislocations in the e-beam CeO₂ film in the vicinity of individual ledges in the substrate surface. Coherence of the CeO₂ film was locally lost in the step regions of the hill and valley structure. The large patterned steps, which are composed of numerous adjacent ledges in the LaAlO₃ surface, caused nucleation of CeO₂ with a tilt misalignment of up to ~5° about the substrate [100]. Nucleation and growth of nonepitaxial CeO₂ crystallites was observed along the step regions of the film during the IBAD portion of deposition. Defect formation in the e-beam ceria layer due to substrate surface relief indicates that "lattice engineering" of multilayer epitaxial structures may not be possible when nonplanar surfaces are created during device fabrication. The IBAD CeO₂ layer was more defective than the conformal layer deposited without the impinging ion beam, even in the portions of the film where epitaxy was maintained throughout both layers.

Unintentional Zinc Diffusion in InP pn-Homojunctions
C.L. REYNOLDS, JR., V. SWAMINATHAN, M. GEVA, L.E. SMITH, and L.C. LUTHER
AT&T Bell Laboratories, 9999 Hamilton Blvd., Breinigsville, PA 18031.

KEY WORDS Diffusion, InP, metalorganic chemical vapor deposition (MOCVD)

Unintentional zinc diffusion into uniformly Si-doped InP layers has been studied. The sharp non-error function Zn concentration profiles and inflections are shown to be consistent with the substitutional-interstitial mechanism when the influence of the electrostatic field of the pn-junction on diffusion is taken into consideration.

Improvement in Dielectric Properties of Low Temperature PECVD Silicon Dioxide by Reaction with Hydrazine
K.W. VOGT, M. HOUSTON, M.F. CEILER, JR., C.E. ROBERTS, and P.A. KOHL
Georgia Institute of Technology, School of Chemical Engineering, Atlanta, GA 30332-0100.

KEY WORDS Anhydrous hydrazine, dielectric properties, plasma-enhanced chemical vapor deposition (PECVD) SiO2

The dielectric properties of plasma-enhanced chemical vapor deposition (PECVD) SiO₂ deposited at 150°C were improved by reaction with anhydrous hydrazine vapor at 150-350°C. The permittivity and loss decreased ~32% and ~86%, respectively, after reaction with hydrazine at 150°C. The decrease in permittivity and loss correlated with a decrease in the dipole concentration (silanol + water). During exposure to humid conditions, water uptake in the SiO₂ films degraded the dielectric properties. A nitrogen anneal at 350°C did not improve the dielectric properties of the PECVD SiO₂. Although water was removed from the films, silanol remained. When the PECVD SiO₂ deposited at 150°C was reacted with hydrazine vapor at 150°C, both silanol and water were removed from the films. The dielectric properties and resistance to water absorption improved.

Epitaxial Lift-Off of Thin InAs Layers
JOEL FASTENAU,¹ EKMEL ÖZBAY,² GARY TUTTLE,¹ and FRAN LAABS²
1--Microelectronics Research Center and Department of Electrical and Computer Engineering, Iowa State University, Ames, IA 50011. 2--Ames Laboratory, Iowa State University, Ames, IA 50011.

KEY WORDS AlSb, epitaxial lift-off, GaSb, InAs

We describe the use of the epitaxial lift-off technique to remove thin layers of InAs from the GaAs substrates on which they were grown and subsequently bonded to glass and silicon substrates. Lift-off was accomplished by taking advantage of the high etching selectivity between AlSb and InAs in an aqueous hydrofluoric acid etching solution, allowing a thin layer of AlSb to serve a sacrificial layer to facilitate the lift-off of the InAs. The InAs layers were transferred with little measurable effect on the electrical and structural properties of the films, as evidenced by Hall effect and x-ray measurements. The technique can easily be extended to transfer more-complex GaSb/AlSb/InAs structures.

Atmospheric Pressure Chemical Vapor Deposition of Blanket Tungsten Films on Silicon Substrates for Integrated Circuit Applications
M.S. HAQUE, U.V. PATEL, H.A. NASEEM, and W.D. BROWN
Department of Electrical Engineering, High Density Electronics Center (HiDEC), University of Arkansas, Fayetteville, AR 72701.

KEY WORDS Chemical vapor deposition (CVD), thin films, tungsten

Atmospheric pressure chemical vapor deposition (APCVD) of tungsten films using WF₆/H₂ chemistry has been studied. A statistical design of experiments approach and a surface response methodology were used to determine the most important process parameters and to obtain the best quality film possible in the parameter range studied. It was found that the deposition rate depends strongly on WF₆ flow rate, temperature, and the interaction between hydrogen flow rate and temperature. The resistivity was found to have a strong dependence on WF₆ and H₂ flow rates and temperature. An activation energy of 0.4 eV was calculated for the reaction rate limited growth regime. Empirical equations for predicting the deposition rate and resistivity were obtained. The resistivity decreases with both increasing film thickness and grain size. The films grown in the studied process parameter range indicate that (110) is the preferred orientation for films deposited with low WF₆/H₂ flow rate ratios at all deposition temperatures (350-450°C), whereas, the (222) orientation dominates at high WF₆/H₂ flow ratios and high deposition temperatures. Also, the grain size is larger for (222) oriented films than for (110) oriented films. The results of this study suggest that high-quality, thin film tungsten can be deposited using APCVD.

An Electrical Method to Characterize Thermal Reactions of Pd/GaAs and Ni/GaAs Contacts
H.F. CHUANG, C.P. LEE, and D.C. LIU
Department of Electronics Engineering and Institute of Electronics, National Chiao Tung University, Hsinchu, Taiwan, Republic of China.

KEY WORDS Activation energy, diffusion coefficients, Schottky contacts

Capacitance-voltage (C-V) and current-voltage (I-V) measurements were used to study the thermal reaction of Pd/GaAs contacts and Ni/GaAs contacts. The thickness of GaAs consumed by the metal/GaAs reaction during annealing was calculated from C-V analyses and I-V analyses. For annealing temperatures below 350°C, the Schottky characteristics of the diodes were good but the electrical junction moves into the GaAs after annealing. The amount of junction movement was calculated directly from our measurements. The diffusion coefficients of Pd and Ni in GaAs at 300°C were estimated both to be around 1.2 x 10^-14 cm²/s.

A Study of Self-Aligned Formation of C54 Ti(Si_1-yGe_y)₂ to p⁺ and n⁺ Si_0.7Ge_0.3 Alloys Using Rapid Thermal Annealing
S.P. ASHBURN,¹ M.C. ÖZTÜRK,¹ G. HARRIS,² and D.M. MAHER²
1--Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695-7911. 2--Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-7916.

KEY WORDS Chemical vapor deposition (CVD), germanide, germanosilicide, LPCVD, rapid thermal annealing (RTA), RTCVD, self-aligned silicide, silicide, titanium

In this paper, solid state reactions of titanium with boron and phosphorus doped Si_0.7Ge_0.3 alloys have been investigated for application in a self-aligned germanosilicide process. Wet chemical etching of the germanosilicide with respect to unreacted Ti in a solution of 1:1:5 NH₄OH:H₂O₂:H₂O has been investigated. Characterization was performed using four-point probe sheet resistance measurements, x-ray diffraction, cross-sectional transmission electron microscopy, Nomarski optical imaging, and scanning electron microscopy. The C54 Ti(Si_1-yGe_y)₂ phase was observed to form for reactions on both boron and phosphorus doped Si_0.7Ge_0.3 alloys. Grain structures of the C54 phases were found to be similar to grain structures of intrinsic alloy reactions with lateral grain dimensions on the order of 0.3 µm. Resistivities of 22 µ-cm have been determined for the boron and phosphorus reactions. Although the germanosilicide phases were observed to etch slowly in 1:1:5 NH₄OH:H₂O₂:H₂O, which is conventionally used in the self-aligned titanium silicide process, the much higher etch rate of titanium nitride compounds and unreacted Ti provided for a self-aligned germanosilicide process. A first anneal in a nitrogen ambient was found to be necessary to eliminate lateral silicidation over surrounding oxide during self-aligned germanosilicide formation.

Strain from Modified Interface Compositions in InGaAs/lnP 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 InP/InGaAs, metalorganic chemical vapor deposition (MOCVD), superlattice

Thin strained regions have been inserted at the interfaces of lattice-matched InGaAs/lnP superlattices to assess growth conditions for tailoring of localized compositional changes and for studying As-P intermixing behavior during heterojunction growth. Also, precise growth rates of binary composition layers were determined from specially designed superlattices using strained layers of common anion compounds inserted periodically into InP and GaAs. Growth rates of fractional monolayers are found to be identical to thick layer growth rates. When thin InAs, GaAs, GaP, AlAs, or AIP layers were inserted at the InGaAs/lnP heterojunctions, the measured strain at either one or both interfaces was equal to the strain predicted from the growth rate x time product. Excess strain seen in some cases is due to a change in As-P intermixing and this component can be separated from the predicted strain. Insertion of Ga-compounds at the InP-grown-on-InGaAs interface causes interface roughening which degrades the superlattice. For all other compositions the thin, highly strained regions are not detrimental to the crystalline quality of the periodic structure.

The Growth and Characterization of AlGaAs Double Heterostructures for the Evaluation of Reactor and Source Quality
M.R. ISLAM,¹ R.V. CHELAKARA,¹ J.G. NEFF,¹ K.G. FERTITTA,¹ P.A. GRUDOWSKI,¹ A.L. HOLMES,¹ F.J. CIUBA,¹ R.D. DUPUIS,¹ and J.E. FOUQUET²
1--Microelectronics Research Center, MER 1.606D-R9900, The University of Texas at Austin, Austin, TX 78712-1100. 2--Hewlett-Packard Laboratories, 3500 Deer Creek Road, Palo Alto, CA 94303-0867.

KEY WORDS AlGaAs, metalorganic chemical vapor deposition (MOCVD), nonradiative centers, oxygen, recombination

AlGaAs double heterostructures are grown by low-pressure metalorganic chemical vapor deposition to evaluate the level of oxygen contamination in different trimethylaluminum sources. Effects of arsine purifiers, misoriented substrates, atmospheric exposure of the growth chamber, and possible phosphorus contamination are also studied. Extensive characterization is performed on these films by a variety of methods, including high-resolution x-ray diffraction, photoluminescence (PL), time-resolved photoluminescence, and secondary-ion mass spectrometry. The PL intensities for structures grown with the low-alkoxide grade are reproducibly much greater than those grown with the regular-grade TMAl. The use of AsH₃ purification improves the PL intensity.

Characterizing Electric Fields in (111)B InGaAs Quantum Wells Using Electric Field Modulated Photoluminescence and Reflectance Techniques
RICHARD L. TOBER, THOMAS B. BAHDER, and JOHN D. BRUNO
U.S. Army Research Laboratory, 2800 Powder Mill Road, Adelphi, MD 20783-1197.

KEY WORDS Electroreflectance, photoreflectance, piezoelectric, strained layer quantum wells

We have performed a series of electroreflectance, photoluminescence, and electric-field-modulated photoluminescence experiments to characterize the strain-induced electric fields in (111)B InGaAs/AlGaAs quantum well p-i-n diode structures. A 180° phase change in the lineshapes of electroreflectance spectra of these samples determines when the quantum well is biased to flatband. Using this bias and a depletion model for the diode, the polarization field in the quantum well can be determined. Contrary to expectations, this polarization field increases significantly with increasing temperature. In addition, at fixed temperature, the quantum well transition energies red-shift with increasing excitation intensity when excited by photons of energy higher than the lowest quantum well transition but lower than the AlGaAs diode's bandgap. When excited with photons of energy greater than the AlGaAs bandgap, the transition energy first red shifts then blue shifts with increasing excitation intensity.