Growth of GaAS and InAlAs on High Quality, Epitaxial, NiAl Metal Film
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characterized as high quality, single crystal pseudomorphic metal films by using x-ray measurements and transmission electron microscopy (TEM) [4]. The present paper concerns a study of the growth of GaAs on single crystal, pseudomorphic NiAI which had previously been grown on (100) GaAs. InxAlIxAs (x=0.25) grown on lattice relaxed NiAl film was used to help the investigation. The factors controlling the quality of GaAs growth have been investigated. The microstructure of these epilayers has been characterized extensively using TEM. EXPERIMENT The samples used in this study were grown on n+ (001) GaAs substrates in a prototype (four source) version of a Varian Gen-II MBE. All the source materials, including Ni (using a beryllium oxide crucible), were evaporated from MBE effusion cells. The growth rates were calibrated by intensity oscillation of the specularly deflected beam in the reflection high-energy electron diffraction (RHEED) pattern. A GaAs/AlAs pre-structure was first grown on each (001) GaAs substrate at 600°C: a 2500 A silicon doped GaAs buffer layer, followed by an undoped 21A AlAs layer, an undoped 50A GaAs layer, another 21A AlAs layer, and finally a 500 A undoped GaAs layer. The two AlAs layers form a double barrier resonant tunneling diode used for electrical measurements not discussed in this paper. After the arsenic background pressure in the growth chamber was pumped to below I x 10-9 Torr and the substrate was cooled to 1 0°C, a NiAl layer was grown at a growth rate of -0.077 micron/hr. A monolayer-by monolayer growth technique, in which the aluminum and nickel shutters were alternatively opened and then closed, is required for growth of the nickel rich, pseudomorphic NiAI film. Additional details can be found in Ref. 4. The composition of the nickel rich NiAI metal was determined to be -57% nickel by post-growth x-ray and Rutherford backscattering measurements. A GaAs layer was then grown at a deposition rate of -0.185 micron/hr on top of the pseudomorphic NiAI film. The growth temperature of the GaAs overlayer was varied from 250 0 C to 550 0C. By coevaporation of Ni and Al, NiAI films with equal concentration of Ni and Al were grown on the same GaAs/AlAs pre-structure. The first few layers of these films were still grown at II 0OC and then the growth temperature was increased beyond 250 0 C. After one-hour growth, the metal film was relaxed to its equilibrium lattice constant, which was checked by x-ray measurements. InxAl I_xAs (x=0.25) was then grown at a deposition rate of -0.135 micron/hr on the relaxed NiAl film. The indium composition of the InxAlI_xAs was determined by x-ray measurement and Raman scattering [5]. The samples were characterized by TEM in cross section. They were prepared by mechanical polishing, dimpling, and then Ar-ion thinning until perforation. All the crosssectional TEM specimens were prepared using {110} cross sections. The samples were examined in Philips CM20 and EM430 electron microscopes. RESULTS GaAs on pseudomorphic NiAl Figure 1 is a cross-sectional TEM pict
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