The electrical and optical properties of InSe have been investigated with single crystals of the compound. The spectral dependence of the optical absorption coefficient and of the photoconductivity was measured. The optical absorption edge was not sufficiently well defined for the band gap to be estimated unambiguously. The photoconductive response was mostly in the visible, and its sensitivity comparable with that of gray selenium. The thermal activation energy of the electrical conductivity was about 1 ev in what is presumably the intrinsic region; and 0.2 to 0.4 ev, depending on the particular sample, at lower temperatures. Conflicting results for carrier type were obtained from several different experiments.

• Received 1 September 1954

DOI:https://doi.org/10.1103/PhysRev.96.1498