Abstract
We have studied the photoluminescence spectra in both ordered and disordered phases of Ga0.5In0.5P alloy as a function of pressure. We found evidence of a pressure-induced conversion of Ga0.5In0.5P from a direct band gap semiconductor to an indirect band gap semiconductor owing to lowering of the X conduction band valleys relative to the minimum at the zone centre. Raman spectra in Ga0.5In0.5P samples doped with Se donors are reported. In ordered Ga0.5In0.5P electronic Raman scattering from single-particle excitations indicates the existence of a high-density electron gas which is absent in a similarly doped disordered sample.