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.
