Direct-Indirect Crossover in Ga$_{\mathrm{x}}$In$_{\mathrm{1-x}}$P Alloys

Advances in metamorphic growth of high quality Ga$_{\mathrm{x}}$In$_{\mathrm{1-x}}$P ($x$ \textgreater\ 0.5) on GaAs substrates have improved the practicality of using these alloys in visible light emitting diodes and lasers. The wavelength range over which these materials are efficient light emitters is determined by the direct-indirect crossover energy, yet considerable discrepancies still remain in the literature regarding the precise crossover composition, $x_{C}$. We revisit this topic and present new experimental results that precisely pinpoint the crossover composition without extrapolation of the direct and indirect bandgap trends. Observation of concurrent yet distinct direct and indirect transitions in the 2 K time integrated and time resolved photoluminescence spectra of disordered Ga$_{0.719}$In$_{0.281}$P films places the crossover very near the composition $x_{C} =$ 0.71. This revised value is critical for facilitating realistic engineering of Ga$_{\mathrm{x}}$In$_{\mathrm{1-x}}$P alloys for light emitting and photovoltaic applications.