GaSb and GaSbxAs1-x single crystal thin films were successfully grown by molecular beam epitaxy. Undoped GaSb showed p-type conduction, and Te was found to be effective as a donor impurity for the MBE-grown GaSb. An in-depth profile of the electrical property of these films revealed that many defects are contained in the epitaxial layer near the interface between the grown layer and the substrate. GaSbxAs1-x films with entire composition were prepared, and the energy gap measured by photoabsorption shows a downward bowing as a function of the composition.
The possibility of S-doping MBE-GaSb using H2S gas has been demonstrated. The sulfer atoms are thermally dissociated from the H2S gas, and are adsorbed at Sb vacancy sites. The S sticking coefficient depends on the Sb coverage. The electron mobility of S-doped GaSb is relatively low. This may be caused by a high compensation ratio and lattice mismatch between the GaAs substrate and the GaSb film. From the experimental results, the activation energy of the S-donor is estimated to be about 75 meV.
High-quality single crystal GaN films have been obtained by RMBE method using the reaction of Ga with NH3. Then, the addition of ionized N2 with decreasing NH3 improved the electrical properties of GaN. Residual H2 decomposed from NH3 has been disturbing the GaN growth and promoting generation of nitrogen vacancies and the complexes.
Thin crystalline films of InAs have been heteroepitaxially grown on (100) surface of GaAs by molecular beam epitaxy. The films are evaluated by optical microscope, SEM, RHEED and electrical measurements. In spite of the existence of a large lattice mismatch between InAs and GaAs, specular InAs films are obtained. Undoped InAs films show the n-type conduction, and their electron concentrations and mobilities are varied depending on the substrate temperature (Ts) during growth. At Ts=480°C, single crystalline films with high crystallographic quality and flat surfaces are grown. Furthermore, Mg atoms are successfully doped into InAs during the MBE growth to obtain p-type films.
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