Optical and photovoltaic properties of indium selenide thin films preparedby van der Waals epitaxy

Indium selenide thin films have been grown on p-type gallium selenide singl e crystal substrates by van der Waals epitaxy. The use of two crucibles in the growth process has resulted in indium selenide films with physical prop erties closer to these of bulk indium selenide than those prepared by other techniques. The optical properties of the films have been studied by elect roabsorption measurements. The band gap and its temperature dependence are very close to those of indium selenide single crystals. The width of the fu ndamental transition, even if larger than that of the pure single crystal m aterial, decreases monotonously with temperature. Exciton peaks are not obs erved even at low temperature, which reveals that these layers still contai n a large defect concentration. The current-voltage characteristic of indiu m selenide thin film devices was measured under simulated AM2 conditions. T he solar conversion efficiency of these devices is lower than 0.6%. The hig h concentration of defects reduces the diffusion length of minority carrier s down to values round to 0.2 mum. (C) 2001 American Institute of Physics.