Multi-exponential analysis of DLTS

Abstract

Deep-level transient spectroscopy (DLTS), which is widely used to characterize deep impurity centers in semiconductors, assumes a single exponential wave form for the transient junction capacitance. When there are several closely spaced energy levels this assumption is no more valid, and the conventional DLTS may lead to errorneous results. To overcome this difficulty we propose here a novel method which we call the multi-exponential DLTS(MEDLTS). The transient wave form of the junction capacitance is directly analysed into multi-exponential compouents using the nonlinear least-squares analysis program “DISCRETE” developed by Provencher. The resolved time constants τ of these components are then displayed in the form of aT2τ−1/T plot. According to the results of simulation with various parameters MEDLTS is shown quite effective to resolve closely spaced energy levels which can not be resolved by the conventional DLTS. As an example of the application of this method deep levels in Si: Au were investigated. The results have shown that a single peak in conventional DLTS actually consists of two adjacent levels with activation energies and capture cross-sectionsEB1=0.49 eV,σB1=1.1×10−14cm2 andEB2=0.46 eV,σB2=1.3×10−15 cm2 and with amplitude ratio 1∶1.