Optical properties of layered III–VI semiconductor γ -InSe: M ( M =Mn, Fe, Co, Ni)

Indium selenide belongs to layered III–VI semiconductors with highly anisotropic optical and electronic properties. Energy gap of 1.32eV makes this material very attractive for solar energy conversion. We investigated the influence of 1% 3-d transition metals M=Mn, Fe, Co, Ni, used as dopants, on energy levels of InSe:M in the range 1.4–6.5eV and especially in the range of energy gap <1.4eV by means of ellipsometric measurements. It was concluded that at ambient temperature foregoing dopants, all divalent, with 4s2 valent electrons, in the similar way influenced on blue-shift of energy levels in valent zone, but did not influence on the fundamental energy gap. Photoluminescence measurements confirmed blue-shift of the valent zone energy levels and an existence of deep impurity levels.