Deep level transient spectroscopy analysis of spatially dependent doping profiles

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Abstract
The study of deep level semiconductor defects frequently employs deep level transient spectroscopy (DLTS), a technique developed for structures with constant doping concentration profiles. In this paper, the theory of the DLTS measurement is extended to the more general case in which both the doping profile and the trap profile vary with depth. This analysis yields a method of calculating exact DLTS transients for the general case, and by its application to several examples, demonstrates that the doping profile shape and the measurement conditions are both factors which determine the degree to which the DLTS transient can be approximated by an exponential. The structures which do exhibit approximately exponential DLTS transients include several which arise in the course of device processing. This study shows that in such structures, a knowledge of the doping profile and the general form of the trap profile can be combined with the standard DLTS boxcar sampling method to obtain trap profile information in addition to the trap activation energy and capture cross-section data.