Selective growth of GaAs and Al0.35Ga0.65As on GaAs patterned substrates by HCl assisted low pressure metalorganic vapour phase epitaxy

The selective epitaxy of GaAs and (Al,Ga)As on a patterned substrate has been achieved using HCl in the vapour phase. As a first approach, HCl assisted growth of GaAs and Al0.35Ga0.65As on GaAs free and stripe patterned substrates has been performed. In addition to the expected anisotropic growth, a strong enhancement of the growth rate was observed. The relation between electronic quality of grown materials and Cl(Al + Ga) ratios in the vapour phase studied using low temperature photoluminescence and Hall effect measurements shows that slight amounts of HCl in the vapour phase lead to improved GaAs and (Al,Ga)As layers. The solid composition of (Al,Ga)As alloys presents a strong dependence upon Cl(Al + Ga) ratios, correlated to the competition between aluminium and gallium chlorides formation in the vapour phase. A thermodynamic analysis of the vapour phase, assuming equilibrium conditions is presented.