Optical and Electron Paramagnetic Resonance Characterization of Point Defects in Semiconductors
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Point defects in two semiconductor materials, both with promising optical properties, are investigated. The first material, CdSiP2, is a nonlinear optical material in which absorption bands due to point defects can hinder performance when used in frequency conversion applications in the infrared. The second material, Sn2P2S6, is a photorefractive material where point defects with specific properties are needed to optimize response in dynamic holography applications. Electron paramagnetic resonance (EPR) spectroscopy is used to identify the electronic structure of defects and their charge states. Correlations between EPR spectra and optical absorption allow assignments for the primary absorption bands in CdSiP2. This research established that singly ionized silicon vacancies in CdSiP2 (VSi-) are responsible for three unwanted absorption bands peaking near 800 nm, 1.0 μm, and 1.9 μm. Two new acceptor defects were identified in CdSiP2: the neutral silicon-on-phosphorus antisite (SiP0) and the neutral copper-oncadmium (CuCd0). These defects are associated with two additional broad photoinduced optical absorption bands appearing at 0.8 μm and 1.4 μm. A series of new point defects have been identified in tellurium-doped Sn2P2S6 crystals using EPR. An iodine ion on a phosphorous site and a tellurium ion on a Sn site are trapped-electron centers. Five trapped-hole centers involve Te ions replacing sulfur ions. The g-matrix has been determined for each of the new paramagnetic defects in Sn2P2S6 and models are assigned.