Photoresponse spectral investigations for anisotropic semiconductor InSe

Photoresponse spectra of anisotropic InSe crystals are investigated depending on the orientation of an illuminated sample surface with respect to light direction. We have detected the differences in the photoresponse spectra in the E || C and E 1 C configurations. They consist in a different energy location of the long-wave edge of the fundamental absorption, the shift is 0.13 eV, as well as their shape. The room temperature presence of an intensive narrow peak at the edge of the photoresponce spectra was only observed in the E||C configuration and is connected to excitonic absorption. Its excitonic origination is confirmed by the low-temperature measurements. In the framework of the three-dimensional model of excitons we have determined the binding energy of direct excitons equal to 65 ± 1.8 meV. It is established for the effect of photopleochroism to be observed at the illumination of the (110) surface by an in-plane polarized light. In the wavelength range 1.03-1.06 μm a measured coefficient of photopleochroism has the value of about 60% and is caused by the anisotropic properties of layered InSe.