Picosecond and Steady State Spectroscopy of Defects in Semi-Insulating Cadmium-Selenide

The goal of this thesis was to understand how defects control the dynamics of electrons in a semiconductor under optical excitation. Time resolved and steady state spectroscopy showed that defects determine the optical and electrical properties of undoped, semi-insulating (SI) CdSe. Nonlinear photoluminescence, picosecond recombination, induced dichroism, the Kerr effect and two step absorption were measured. The important physics in this work was characterizing the three defect bands that cause these effects in SI CdSe. First, the main recombination center is a deep donor (R), (DBLTURN)1.3 eV above the valence band, with very large cross sections for free carrier capture. This level R has degenerate levels, as shown by the induced dichroism. Second, a shallow acceptor (A), 105 meV above the valence band, is also a recombination center. Third, a conduction band tail (T), consisting of shallow donors, is a luminescence center. Comparisons between undoped low resistivity CdSe and SI CdSe suggest these levels also cause the high resistivity properties of SI CdSe. A two level model by Klasens, using both R and A, explains the nonlinear photoluminescence under low intensity, steady state excitation. Models, using these defect levels, were constructed that explain the picosecond results. The methods and theories developed in this thesis could be used in the quality control and fabrication of semiconductor devices.