Indirect Absorption Edge of GaS under Uniaxial Pressure

Optical absorption spectra of layered compound GaS are measured near the indirect edge under uniaxial pressure parallel to the c -axis (perpendicular to the layer) at 4.2 K. The deduced values of the deformation potential for the indirect edge are D i ⊥ =-8.0±2.5 eV and D i // =-2.3±0.4 eV for the strain perpendicular and parallel to the c -axis, respectively. The sign and anisotropy of the deformation potentials obtained here are discussed on the basis of the band model characteristic of layered materials, where the competition between interlayer and intralayer interactions determines the pressure dependence of their band gaps.