PHOTOLUMINESCENCE EXCITATION SPECTROSCOPY YIELDS BAND-GAP OF GA0.5IN0.5P CONTAINING RELATIVELY ORDERED DOMAINS

Photoluminescence excitation spectroscopy at 9 K reveals that the abso rption edge of Ga0.5In0.5P containing relatively ordered domains (grow n at 670-degrees-C) is near 1.93 eV, representing the band gap of this inhomogeneous material. Photoluminescence (PL) has been observed at e nergies lower than this absorption edge energy by up to 70 meV. Along with the unusually slow decay times previously measured, the low energ y PL indicates spatially indirect recombination. Therefore PL alone ca nnot reliably determine the band gap of typical ''ordered'' Ga0.5In0.5 P samples. In contrast, the optical properties of relatively randomly ordered (''normal'') Ga0.5In0.5P (grown at 775-degrees-C) are typical of a normal direct III-V semiconductor.