Effect of substrate orientation on the defect-induced bound exciton emissions in GaAs grown by molecular beam epitaxy

The dependence of photoluminescence (PL) spectra at 2 K on the substrate orientation is reported for GaAs grown by molecular beam epitaxy (MBE). Samples investigated are GaAs grown on (n11)A- and (n11)B-oriented substrates where n is 2, 3, 5 and 9, and those on (321)A- (110)B- and (100)A-oriented ones. It was demonstrated that emissions denoted by defect-induced bound excitons (DIBE) present strong crystal orientation dependence. In the (n11) series, DIBE was enhanced peculiarly in (211)A and (311)A substrates and two sharp emissions denoted by t^* and v₃ were specifically observed there, but they were completely quenched for the (211)B substrate. When n exceeds 3, DIBE was observed ubiquitously in (n11)A and (n11)B substrates. The (321)A substrate indicated a most idiosyncratic DIBE with a strong enhancement of t^* and v₃. These results show that the spectral features pertinent to DIBE fully reflect the whole stacking process of impinging molecular beams on the growth front which is governed by the surface structure inherent to the surface dangling bonds of the substrate.