Fundamental studies of lattice mismatched, strain-free Ga$_{x}$In$_{1-x}$P alloys for x $>$ 0.51

Fundamental electronic and optical properties of the Ga$_{x}$In$_{1-x}$P alloy system are investigated for applications requiring high bandgaps in the range of $\sim $1.9--2.2 eV, corresponding to the composition range 0.51$<$x$<$0.8. Samples were grown by metalorganic vapor phase epitaxy (MOVPE) on GaAs substrates. To achieve the nearly-strain-free, lattice-mismatched compositions with higher bandgaps, the samples were prepared by first growing a thick step-graded layer of GaAs$_{1-y}$P$_{y}$ to bridge the lattice misfit between the Ga$_{x}$In$_{1-x}$P layers and the GaAs substrate. Phenomena such as spontaneous long-range ordering and intermixing of $\Gamma $-L-X bands near the direct-indirect crossover were studied using high resolution x-ray diffraction, modulated electro/photo-reflectance, and time-resolved photoluminescence techniques at various temperatures. The results will be discussed within the context of using these high bandgap alloys as light emitting diodes (LEDs) emitting within the green gap.