Transient photoconductivity measurements in semi-insulating GaAs. I. An analog approach

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Abstract
An experimental arrangement is described by which emission coefficient behavior associated with deep-level traps in semi-insulating GaAs can be surveyed, from the photoconductive transient behavior following a trap-filling light pulse. This method, often referred to as PITS (for photoinduced transient spectroscopy) has analogies with the transient capacitance spectroscopy usable for conductive material, but some significant differences also. The necessary experimental precautions which can maximize the probability of getting reliable data are described, and illustrated by PITS results obtained with bulk semi-insulating samples of Cr-doped GaAs. Those results include data for five kinds of trap with activation energies from 0.3 to 0.8 eV, of which some are readily identifiable and others are not. The method described in this paper relies on analog measurement of the change in sample voltage during a specified time interval of the photoconductive decay.