Optical absorption and emission of GaP1−<i>x</i>Sb<i>x</i> alloys

Abstract

The first detailed optical investigation of the metastable III/V semiconductor alloy GaP1−xSbx is presented. Epilayers are grown by atmospheric pressure organometallic vapor phase epitaxy throughout the entire compositional range on GaP, GaAs, and GaSb substrates. The approximately 1-μm-thick layers are partially strained with values of lattice mismatch as large as 1.7×10−2. Values of band gap are determined for the first time from absorption spectra measured at 10 and 300 K and corrected for strain-induced energy shifts. The resultant values of bowing parameter for the direct and indirect band gaps are cΓ=3.11±0.18 eV and cx =2.06±0.18 eV, independent of temperature, yielding a value of direct/indirect crossover composition, xc, of 0.32±0.07. Single photoluminescence (PL) peaks are observed between 10 and 300 K for all samples. For samples with 0.37≤x≤0.47, they are assigned to recombination of carriers localized in bandtail states induced by compositional fluctuations. The stretch of the tails into the gap is greatly enhanced over the random alloy limit by the metastability of the Ga1−xSbx alloys. PL peaks for samples with x≤0.32 are assigned to recombination via deep centers in the gap. The PL peak of a sample with x=0.91 is assigned to recombination involving shallow acceptors.