Comparison of isothermal and boxcar methods of analysis of photocurrent transients

Abstract

Analysis of photocurrent transients to obtain information on deep levels in semi-insulating gallium arsenide is known as optical transient current spectroscopy (OTCS). Mostly a boxcar amplifier technique has been employed. It is suggested that, because the geometries which have been used may not produce the physics assumed in the method as originally proposed, the assumptions on which the boxcar technique is based may not be satisfied. To test this, digitally recorded transients over a range of temperature were analysed using an improved isothermal analysis method and a software-simulated boxcar. The latter was found to give anomalous trap signatures, particularly when 'negative transients' were concerned, and to resolve fewer levels than the isothermal method. Analysis of the parameters of the decays observed by the isothermal method showed that the boxcar assumptions were indeed not satisfied.