Optical nonlinearities and carrier dynamics in semi‐insulating crystals

Abstract

We analyze conditions when the deep‐impurity governed carrier generation and transport in semi‐insulating crystals create the coexisting free carrier, photorefractive, and absorptive nonlinearities. By monitoring the nonequilibrium carrier and space charge field dynamics via the probe beam diffraction on transient gratings, number of electrical parameters in bulk semi‐insulating crystal have been determined, as carrier lifetime, diffusion coefficient, diffusion length, and sign of carriers, photogenerated from deep traps. We show a novel possibility to record a transient reflection grating via spatial modulation of the deep trap occupation and applicability of this technique to evaluate the compensation ratio of these traps as well as their recombination properties. Experimentally measured diffraction kinetics on free carrier, photorefractive and absorptive gratings in few nanosecond time interval provided the values of diffusion coefficient and carrier lifetime in bulk CdTe and ZnTe crystals, doped by V, Ge, Al, Sc as well in InP:Fe. Carrier transport peculiarities in these crystals revealed the type (n or p) of dominant carriers, generated from the deep impurity levels. In n‐type HVPE GaN crystals, we observed impact of light‐induced space‐charge field to carrier diffusion. The transient reflection gratings in semi‐insulating CdTe:V allowed discrimination of deep trap governed carrier recombination rate from the other recombination channels. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)