Optical beam induced phenomena in semiconductors
This thesis is concerned with the interaction of a finely focussed light beam and a semiconductor. The object of the work is to develop a consistent theory which explains the formation of both the optical beam induced current and photoluminescence signals with a view to using these techniques to characterize semiconductor materials. Here we extend previous theories by considering a light beam which is focussed through a lens of finite numerical aperture. Expressions are derived which give the distribution of excess minority carriers injected into a semi-infinite semiconductor by the focussed light beam. The injected minority carrier distribution is then used to predict the imaging properties of the optical beam induced current and photoluminescence techniques when used to image electrically active defects in semiconductors. High resolution scanning photoluminescence images of indium phosphide are presented showing a resolution which is in good agreement with theory. The form of both the steady state and time dependent optical beam induced current in Schottky barrier diodes, planar junction diodes and devices where the p-n junction is perpendicular to the semiconductor surface is derived. Various methods are suggested for measuring the minority carrier diffusion length and lifetime. An extension to previous analyses is given by considering the effect of scanning the light beam, at some arbitrary velocity, on the form of the optical beam induced current collected by a p-n junction either parrallel or perpendicular to the semiconductor surface. It is also shown how the scan speed can effect the imaging of electrically active defects producing a contrast function which is asymmetric and reduced in magnitude. An analysis of the photoluminescence signal generated from a semi-infinite semiconductor by a finely focussed light beam is given. Various methods based on the photoluminescence technique are suggested for measuring the minority carrier lifetime.