Undoped semi-insulating InP can be obtained by high-pressure annealing of high purity materials. The reproducibility was however not satisfactory. In the present work, we found that not only Fe concentrations but also Cr and Ni concentrations in annealed wafers were slightly increased. In order to reduce the contamination, conductive InP with a trace amount of Fe was annealed under low phosphorus vapor pressure. The minimum Fe concentration for realizing semi-insulating InP was found to be 1/spl times/19/sup 15/ cm/sup -3/. It was also found that annealing conditions largely affect the resistivity uniformity of undoped semi-insulating InP.
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