Optimization of the surface morphology of GaAs epitaxial layers grown by close-spaced vapor transport

Abstract

GaAs epitaxial layers were grown on (100) GaAs and vicinal substrates (2° off (100) toward (110)) by close-spaced vapor transport (CSVT) using water vapor as transport agent. We demonstrate that the temperature at which water vapor is injected into the reactor, Tinj, is a criticial parameter for the layer morphology. Furthermore, the optimum Tinj, is a function of water partial pressure, [Formula: see text]. For each [Formula: see text], there is a Tinj range for which specular layers are obtained. This range is defined for [Formula: see text] Torr (1 Torr = 133.3 Pa). The only defects appearing on the specular layers grown on (100) GaAs substrates are oval hillocks (structureless oval defects, and occasionally oval plateaus and oval defects with a faceted central core head). All oval hillocks have their long axis, L1, parallel to < 110 >. By measuring L1 and L2 (the short axis of the defect, perpendicular to L1), lateral growth rates of GaAs are obtained. They vary with [Formula: see text]. At high [Formula: see text], [Formula: see text] is 1 at low water vapor pressure. All oval hillocks result from the contamination of the substrate surface. By using vicinal GaAs substrates, the oval hillock density was decreased to about 500 cm−2, a result similar to that obtained with molecular beam epitaxy.