Abstract
Thermally stimulated current (TSC) spectra and photocurrent (Ipc) measurements are used for determination and evaluation of deep levels, as well as for the comparison of their distributional uniformity in undoped semi-insulating (SI) GaAs crystals. Liquid-encapsulated Czochralski-grown (LEC) GaAs wafers from various sources were analysed. It was found that crystal growth and post-growth treatment of samples from each producer give characteristic and distinctive TSC spectra. The samples from different positions at wafers show good uniformity of deep-level distribution for some producers, whereas the uniformity is quite poor for the others. Some characteristic peaks appear in spectra of all crystals, suggesting either the presence of native defects or some of the most common contaminants. The results obtained are compared with those in previous reports. Furthermore, a considerable difference in photocurrent values after 100 s illumination has been found, indicating large free carrier lifetime scattering for samples of different origins. This study shows how, by using quick and simple TSC and Ipc measurements, the quality of the material and uniformity of the distribution of defects with deep levels in the forbidden energy gap can be assessed.
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