Abstract
The temperature dependence of photorefractive two-wave mixing gain and the diffraction efficiency in semi-insulating InP:Fe samples are studied. Results from four samples grown under nominally similar conditions but with different compensation ratios are presented. Marked deviations from the single-defect model of the photorefractive effect are observed for some samples. We show that multiple defects can produce a strong electron–hole competition that can change the sign of two-wave mixing gain and quench four-wave mixing as a function of temperature. A two-defect model is used to describe the observed behavior and its effect on the intensity- and temperature-dependent balance condition. This temperature study also shows that the indirect electron–hole competition caused by carrier promotion from the valence band directly to the excited state of Fe2+ has little influence on the photorefractive effect. Samples taken from the tail sections of the InP boules, where the Fe concentrations are highest, are consistently found to have higher gains than samples taken closer to the seed end.
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