Design of a stress-dependent deep-level transient spectroscopy instrument for the study of the structural properties of defects in semiconductors

Abstract

Defects in semiconductors have been studied extensively over the past few decades. The advent of highly sensitive techniques such as deep-level transient spectroscopy (DLTS) and Laplace DLTS (LDLTS) has resulted in more accurate measurements of the electrical properties of defects, as well as contributed towards identi cation of new ones. However, the bulk of the research e orts on this topic is concentrated on the electrical properties and not the physical structure of defects. While numerous characterization techniques, such as EPR and IR spectroscopy can be used to study the structure of defects, application of uniaxial stress with DLTS has been shown to be a superior technique with regards to determining the symmetry of defects observed by DLTS. However, in practice, it is a di cult and time consuming technique to perform, and therefore is not a popular research tool. There are only a few such systems that are operational in the world. The di culties arise from preparation and mounting of the samples as well as stability of the system and survival of the samples during and after each measurement. The aim of this work is to undertake the design of a stress-dependent LDLTS system that is user friendly and can provide reproducible results. The speed with which samples can be mounted and dismounted was another point of interest during the design process and the higher resolution of LDLTS compared to conventional DLTS makes it possible to perform measurements with lower amounts of pressure, thus increasing the survive ability of the samples. Furthermore, proper functioning of the system was investigated by attempting to reproduce a stress-dependent study on the E2 defect in GaAs that was done using a similar instrument that utilized a conventional DLTS system. The results clearly con rm the superiority of LDLTS for this type of measurements. Where in the previous study only a broadening of the DLTS peak is observed under 0.4 GPa, in our measurements there is a clear splitting of the emission rate spectrum from one into two separate components when stressed along the (110) axis at only 0.18 GPa and the results numerically agree with the aforementioned study. The most important shortcoming of the system is temperature stability at low temperatures.