Effect of order/disorder near the $\Gamma $-L and L-X crossovers in the conduction band of lattice-mismatched Ga$_{x}$In$_{1-x}$P alloys*

In this work we have studied the effect of order/disorder on the $\Gamma $-L and L-X crossover points in the conduction band of Ga$_{x}$In$_{1-x}$P alloys, using polarized photoluminescence and electroreflectance techniques at various temperatures. Ga$_{x}$In$_{1-x}$P samples (x=0.25-0.78) were grown by atmospheric pressure organometallic vapor phase epitaxy (OMVPE). Some samples were grown directly on a miscut GaAs substrate while in other samples a thick GaAsP step-grade was grown first, to reduce the dislocation density. The significance of the crossover point in the conduction band of the alloy for the efficiency of devices such as multijunction high-efficiency solar cells and light emitting diodes will be discussed.