The influence of hydrostatic pressure on the fundamental absorption edge of crystals with TlSe-type structure

Monocrystalline TlSe, TlInSe2, and mixed crystals (M) TlInSe/sub 2(1-x)/S/sub 2x/ (0 < = x < = 0.25) were grown and their transmission spectra were measured in the pressure range from 105 to 5.5 x 108 Pa. In order to get information about the pressure behaviour of energy band gaps the absorption spectra were analyzed with the formula (α h ν)/sup m/ proportional to h ν - E/sub g/ (m = 1/2 and 2/3 for allowed indirect and forbidden direct transitions, respectively). Both in TlSe and in mixed crystals M the indirect and direct band gaps linearly decrease with pressure. The pressure coefficient dE/sub g//sup i//dP of mixed crystals M decreases with increasing sulphur conenctration