A novel computer based pseudo-logarithmic capacitance/conductance DLTS system specifically designed for transient analysis

Abstract

A new inexpensive, simple to construct, PC based deep level transient spectroscopy (DLTS) system has been developed that efficiently digitizes and analyzes capacitance and conductance transients by conventional DLTS methods (boxcar, rectangular, and exponential) as well as by several transient methods (nonlinear least squares, modulation function methods, and correlation method of linear predictive modeling). A unique "pseudo-logarithmic" sample storage scheme allows each transient to be sampled at more than 11 different rates, permitting 3 to 5 decades of time constants to be observed in one thermal scan allowing the resolution of closely spaced defect energy levels. The high system flexibility allows weighting times (or transient observation times) to be selected between <200 μs to 3 days. This is the first report that details the merits, including faster response and recovery times, of using the new Boonton 7200 capacitance meter in a DLTS system. This is also the first reported use of the pseudo-logarithmic sample spacing to enhance the range of time constants observable in a single thermal cycle as well as the first use of selectable resistance values in conjunction with selectable capacitance values to allow the conductance and capacitance to be sampled simultaneously in high resolution mode (<1 fF and <0.01 μS). It is shown experimentally that the transient analysis capability of this system can separate closely spaced deep levels where the conventional DLTS methods fail.