Structure property anisotropy in lattice-mismatched single heterostructures

Anisotropic optical, electrical, and structural properties have been observed in thick In_xGa_1-xAs/GaAs single heterostructures grown by low-pressure metal-organic vapor phase epitaxy on (001) and slightly misoriented GaAs substrates. The luminescence of the (001) samples is polarized and the electron mobility is higher along one of the 〈110〉 directions. Asymmetric distributions of surface ridges and misfit dislocations have been observed in secondary electron micrographs (SEMS) of the surfaces and in transmission electron micrographs. Strong anisotropy and a clear correlation between the anisotropic optical, electrical, and structural properties have been observed for samples grown on (001) oriented substrates. For (001) samples, the results indicate that the anisotropic properties are induced by nonuniform strain relaxation. For samples grown on misoriented substrates, SEM and micro-Raman spectroscopy indicate a better crystal quality. The anisotropic properties are found to be reversed and the degree of anisotropy is significantly reduced. The results suggest the improvement of interfacial coherency owing to the mechanism of nucleation on a substrate presenting a series of steps and ledges. The reduction of defects within the epilayer can be partly due to a faster strain relief in vicinal (001) epilayers.