Optical cross sections associated with deep levels in semiconductors. I

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Abstract
One of the few direct means of identifying the position of localised states within the band gap of semiconductors entails the measurement of radiative transitions between bound states and the host crystal bands. Studies of the temperature dependence of the spectra supply information from which the phonon contribution can be extracted, but the electronic contribution to the transition probability and its physical signature remain poorly understood. Accordingly, the authors have employed their Green function technique to calculate the electronic components of the optical cross section for deep impurity states in direct (GaAs) and indirect (GaP) gap materials. Localised states transforming as the a1 and t2 representations of the Td point group were considered at several positions in the forbidden gap. A large sampling (compared with that needed for the calculation of binding energies) was employed in order to capture accurately the angular properties of the momentum wavefunction and to ensure convergence of the optical sums. Transitions involving the conduction and valence bands were computed, and some simple trends discussed.