Photoionisation of impurities with deep levels in gallium arsenide

Abstract

A model is proposed to gain a better understanding of photoionisation cross sections of deep impurities in direct-gap semiconductors. The fundamental assumptions of the model are the same as those of the Lucovsky model, but evaluation of the photoionisation cross section is done using accurate semiconductor wavefunctions and bandstructure. For computational ease a planar delta function impurity is used, which induces deep-level states in the semiconductor band gap analogous to surface states. The calculations are performed using evanescent waves, which allows the results to be easily analysed and gives considerable insight into how the photoionisation cross section is determined by the form of the deep-level wavefunction.