Studies deep chromium acceptor levels in InP

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Abstract
Measurements of photoconductivity and secondary excitation spectra have been used to determine the position of the Cr acceptor level in InP. A pair of complementary photoconductive onsets have been observed at 0.40 eV at 300K (0.47 eV at 6K), and at 0.93 eV at both 300K and 6K, which result from the photoexcitation of electrons out of and into the Cr trap level. This level lies 0.40 eV (0.47 eV) below the conduction band edge 300K (6K), which accounts for the relatively low resistance of Cr-doped semi-insulating InP. The trap populations have been changed by using both neutron transmutation doping, and secondary bias illumination. A maximum in the photoconductivity spectrum at 0.81 eV is provisionally interpreted as an intracentre 5T2-5E transition of Cr2+ (3d4), where the upper state is located above the conduction band edge.