Electronic Excitation Processes in Semiconductors.
Final rept. 1 Jun 71-31 May 74,
CASE WESTERN RESERVE UNIV CLEVELAND OHIO
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The purpose of this work is to determine the mechanisms responsible for the fast component of the induced absroption observed by Goto and Langer in CdS crystals subjected to high intensity optical excitation. From qualitative features of the reported absorption spectra it is concluded that the relevant process or processes intimately involves excitons. These absorption processes are described approximately by a two-step mechanism in which the first step consists of the simultaneous annihilation of the photon and the creation of a virtual state in an exciton band. In the second step, the exciton is scattered into its final state. Three scattering agents are considered, namely, longitudinal optical phonons, electrons and holes, and excitons. For the purpose of interpreting the empirical data on the exciton spectra in wurtzite semiconductors, the appropriate effective Hamiltonian for the excitons is set up. Relations between the valence band parameters for a wurtzite crystal and the corresponding zinc blende crystal are established.
- Solid State Physics