PHOTOLUMINESCENCE, PHOTOLUMINESCENCE EXCITATION, AND RESONANT RAMAN-SPECTROSCOPY OF DISORDERED AND ORDERED GA0.52IN0.48P

Ordering in the CuPt structure is known to significantly reduce the ba nd gap of Ga0.52In0.48P as well as induce a number of unusual details in its optical properties, including long, excitation-intensity-depend ent lifetimes and an excitation-intensity-dependent emission energy. W e report photoluminescence (PL), photoluminescence excitation (PLE), a nd resonant Raman measurements performed on ordered and disordered Ga0 .52In0.48P. The dominant high energy emission process at low temperatu re in disordered Ga0.52In0.48P is established to be excitonic, but the exciton trapping energy is not unique. PLE from ordered Ga0.52In0.48P shows significant tailing of electronic states into the band gap and a ''band edge' which depends on detection energy. The dominant radiati ve process in ordered Ga0.52In0.48P is not excitonic. A large increase in the Stokes shift between the absorption edge (band gap) and PL emi ssion peak occurs when the material orders. Hence, low temperature PL is determined to be a particularly poor measure of band gap. Resonant Raman scattering is used to study optical phonons and their coupling t o electronic states. We find that the resonance enhancement at the ban d edge occurs via localized excitons.