Constant-capacitance DLTS measurement of defect-density profiles in semiconductors

Abstract

An analysis is presented for obtaining spatial depth profiles of electronic defects in semiconductors from deep-level spectroscopic measurements performed in the constant-capacitance mode. Combined with the double-correlation technique proposed by Lefevre and Schulz, the new method offers significant advantages for measuring defect profiles. Deep-level transient spectroscopy (DLTS), performed in either the conventional capacitance-transient mode or the constant-capacitance mode, provides the energy levels of defect states in the semiconductor band gap. The double correlation DLTS technique (DDLTS) is used to define a narrow spatial observation window for defect profiling. However, in the DDLTS analysis of capacitance-transient data, specific approximations are required to deal with the change with time of the semiconductor depletion width during the transient response to a charging pulse. In the constant-capacitance mode, the depletion width is held constant by dynamically varying the applied voltage during the transient response, thus permitting more accurate measurements of defect profiles at high trap densities. Analytical expressions for computing the local trap density are derived, and experimental results are presented for damage profiles in self-implanted silicon.