Optical properties and photovoltaic device applications of InSe films

Films were formed by alternately evaporating InSe and Selenium from separate evaporation sources onto glass substrates kept at temperatures below 150°C with subsequent thermal annealing.The effects of the additional selenium on the properties of the films were investigated by structural investigations and photoconductivity measurements. It is found from the results of the present measurements that compositional changes occur in the films with increasing selenium/InSe ratio and that single-phase films containing only InSe are obtained at a certain critical ratio.The refractive indices and absorption coefficients of amorphous and crystalline InSe films in the spectral range 0.6–2.5 μm are determined by spectrophotometric reflectance and transmittance measurements. The minimum optical energy gap obtained from measurements of the absorption spectrum for the crystalline films is close to the value for single crystals.A heterostructure diode using crystalline InSe films as “window layers” was prepared and the fundamental photovoltaic properties were investigated. An absolute quantum efficiency of about 18% is obtained in the wavelength range 1.1–1.25 μm.