Defects with deep levels and their impact on optical absorption of semi-insulating GaAs

Defects having deep levels in the forbidden energy gap of semi-insulating (Si) GaAs play an important role in its low-temperature transient properties (e.g. photoconductivity, absorption, electron paramagnetic resonance (EPR) etc.). Optical absorption time evolutions (transients) for several infrared (IR) photon energies were measured. A simple model, based on dominant deep level EL2 behavior under illumination, was used for the calculation of theoretical absorption transients. The experimental and theoretical results were compared and discussed. It was concluded that qualitative accordance was good and that the model could be successfully used in EL2 initial occupancy estimation. For better quantitative agreement, the model should be improved by additional mechanisms and/or by including some deep levels other than EL2.