Optical Transitions in the Spectra of the Fundamental Absorption and Reflection of InSe Single Crystals

The spectrum of the fundamental absorption and reflection of n‐type InSe single crystals is studied in the energy region 1 to 5 eV and in the temperature range 293 to 90 °K. In the spectrum an absorption is observed which may be related to direct and indicrect interband transitions. The main parameters characterizing the indirect and direct optical transitions are determined. The fine structure in the absorption spectrum due to excitons is investigated. On the basis of the analysis of the optical absorption and reflection properties in the fundamental region and using selection rules, the character of optical transitions as well as the peculiarities in the energy band structure of InSe single crystals are established.