Transient Response of Photorefractive Grating in BSO and GaP by Short Light Pulse

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(1) Both response time and diffraction efficiency versus index grating spacing characteristics were examined for BSO and GaP crystals. The agreement between the theory and experiments is quite good, when the data are analyzed on the basis of the unified band transport model under the initial condition of occupied acceptors. The characteristic wave number of the interference fringe, K_O, at which maximum diffraction efficiency can be obtained under steady state condition, is the most important parameter because it characterize not only the diffraction efficiency versus K curve but also the response time versus K curve. Some physical parameters of those crystals were estimated from those characteristics.(2) Time evolution of the index grating after illumination of a short light pulse was analyzed by using a newly developed "Four- Level" model, where carrier dynamics between conduction band and a donor level, an ionized acceptor level and two shallow acceptor levels is considered on the b … More asis of thermally stimulated current (TSC) measurement for trap identification.(3) Electrical properties of BSO and GaP crystals relevant to photorefractive properties were studied by measuring a newly developed light-stimulated current (LSC), transient photocurrent and thermally stimulated current (TSC). The internal electric field formed after removal of external applied electric field was utilized for TSC measurements, where several deep traps were successfully identified without suffering from noise current.(4) Transient photorefractive properties of a BSO crystal after illumination by short light pulses were studied by monitoring diffracted beam intensity of a He-Ne laser beam. Previously observed peculiar response curve, having a dip between first fast rise and second slower rise, can be explained by a newly developed "Four-Level" model with two shallow acceptor levels, an inactive ionized acceptor level, and a donor level. Temperature dependences of transient photorefractive properties and transient photocurrent also support the present model. Less