Exciton photoconductivity in layered semiconductor GaSe

Anisotropy in exciton photoconductivity in layered gallium selenide (GaSe) crystal was investigated by making use of simultaneous photoconductivity measurements taken parallel and perpendicular to the layers as a function of temperature. Peak positions and line widths of the measured photoconductivity spectrum in either direction were different from those deduced from absorption measurements. Exciton photoconductivity spectrum has a tail in the long wavelength side of the exciton peak. This exponentially increasing photoconductivity tail with photon energy is investigated in the 10–300 K temperature range. Energetical positions of defect and impurity states were studied by using temperature dependence of dark conductivity and by constant photocurrent method, which was employed for the first time in GaSe layered crystals. Results are discussed within the framework of random microelectric field induced by phonons, stacking faults, impurities, and vacancies in the GaSe lattice.