PREPARATION, CHARACTERIZATION, AND PHOTOACOUSTIC ABSORPTION STUDIES OF CUINSE2

Single phase polycrystalline CuInSe2 is prepared by direct fusion of e lements and characterized by X-rap diffraction and Auger electron spec troscopy. Photoacoustic absorption in this semiconducting material yie lds an energy band-gap of 1.05 +/- 0.02 eV. Some structures at 1.03, 0 .95, 0.89, 0.86, 0.81, and 0.79 eV are observed in the photoacoustic a bsorption spectrum which, we believe, are due to defect level transiti ons. The first three levels are identified as due to the free exciton level below the conduction-band edge, donor-acceptor transitions betwe en selenium vacancy donors, and copper on indium antisite accepters an d indium vacancy accepters respectively. The origin of other structure s, at present, remains unidentified. Most probably, these are caused b y the defect levels arising from variation in the stoichiometric compo sition of the compound.