Below-bandgap photoluminescence from GaAs substrates induced by pre-MBE-growth treatments

We report the observation of below-GaAs-bandgap photoluminescence (PL) emission from semi-insulating GaAs substrates subjected to thermal annealing during the standard pre-MBE-growth processes. The below-GaAs-bandgap luminescence from defects were investigated using a combination of PL techniques including below-gap-excitation (BGE) and backside illuminated (BI) PL. Using BGE and BI PL, defects deep within the substrates were probed, and their spatial positions along the sample were analyzed. A PL peak at 1000 nm was observed after pre-bake annealing at 300°C, and further peaks at 905, 940 and 1150 nm were found after oxide desorption annealing at 600°C. These are attributed to the Ga-vacancy related defect, Ga-vacancy-complex defect, As-vacancy defect, and InGaAs states, respectively. This is the first report of the formation of such optically-active defects after annealing of GaAs at moderate temperature ranges (≤600°C), providing guidelines to distinguish desired electronic states for device applications from those that arise from defects which often confuse, and also degrade the device performances.