Twin-free single crystals of iron doped indium phosphide (InP:Fe) have been grown with different concentrations of iron dopants and shallow donor impurities using several techniques: magnetic liquid encapsulated Kyropoulos (MLEK), liquid encapsulated Czochralski (LEC), and vertical gradient freeze (VGF). Iron in InP falls into one of two defect states, and thus can be used as an infrared photorefractive (PR) material for amplifying coherent optical signals. The crystals above were compared in PR experiments at room temperature to measure two-wave mixing gain. The two defect states where then measured by independent means to determine a relationship between PR gain and defect concentration. From an analysis of these data the PR gain can be optimized by growing crystals under conditions which result in InP:Fe with an optimum Fe3+ concentration, optimum Fe3+/Fe2+ ratio, uniform dopant distribution, and low defect density.
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