Photoluminescence studies of vacancies and vacancy-impurity complexes in annealed GaAs

Photoluminescence measurements made at various depths below the surface of annealed GaAs single crystals are compared with vacancy distribution profiles obtained from electrical measurements. Results on undoped n-GaAs indicate that isolated Ga or As vacancies form non radiative centers. A broad-band emission at 1.20 eV, arising from V_Ga-donor complexes, is observed in spectra taken from n-type samples doped with Si, Sn or Te. The intensity of the 1.20eV band varies with depth and reaches its maximum value in the region where Ga vacancies are dominant. These results show the consistency between photoluminescence and electrical measurements. A band at 1.37eV has previously been assigned to V_As-acceptor complexes. This band was observed in this study only when the samples had been annealed in ampoules prepared from quartz containing traces of Cu. It is concluded that the 1.37eV band is due to Cu contamination rather than V_As-acceptor complexes.