Compositional Inhomogeneities in GaAs1−xPx Alloy Epitaxial Layers

Abstract

Inhomogeneities in vapor‐grown epitaxial layers of Ga(As, P) alloys on GaAs substrates were studied by the electron microprobe, the divergent‐beam x‐ray method, and x‐ray topography. The epitaxial layers were prepared by growing a graded composition region between the substrate and the final GaAs_1−xP_x composition. The electron microprobe was used to determine the As/P ratio in the layer by scanning the cleaved edge of the epitaxial layer and substrate. The results showed two types of samples: those with composition steps in the graded composition region and those without these steps. Pseudo‐Kossel patterns for the composition steps as well as for the GaAs substrate and the GaAs_1−xP_x alloy surface layer are seen in the divergent x‐ray pattern photographs. The sharpness of the pseudo‐Kossel lines indicates that the degree of crystalline perfection decreased with increasing phosphorus content of the epitaxial layer. Lang topographs show that the accommodation for the lattice mismatch between the substrate and epitaxial layer results in the formation of bunched edge dislocations which have [011] and$\text{[011̄]}$ Burgers vectors. Finally the influence of the defect structures on the diffusion of zinc into the Ga(As, P) material is shown qualitatively by the nature of the diffusion front. The nature of the defect distribution directly controls the nature of the zinc diffusion front into the Ga(As, P). Increased electroluminescent efficiency of devices produced from the material is directly correlated with the flatness of the diffusion front.