Transmission Electron Microscopy Study of the Compositionally Graded InGaAs Layer

Abstract

Two types of molecular beam epitaxy grown InGaAs/GaAs structures with 1-µ m-thick compositionally graded buffer layer were studied by cross sectional transmission electron microscopy, plan-view transmission electron microscopy and off-axis convergent beam electron diffraction (CBED). The observed misfit dislocations in both structures were distributed in a region from the interface between the graded InGaAs layer and the GaAs buffer layer up to about 0.6 µ m in the graded layer with a density of 1× 109 cm-2. No dislocations were observed to pin at the upper interface between the constant and the graded InGaAs layers or within the constant InGaAs layer itself for the type B structure. Threading dislocations were found to spread over the majority of the graded layer with Burger's vector of a/2<011>. CBED was used to determine the local lattice parameters, and thus the corresponding In composition and relaxation of the layered structures. The accuracy of CBED results was proved by the double crystal X-ray diffraction data when DCXRD was applicable. Tersoff's model was used to determine the residual strain in the graded layer by substituting the measured lattice parameters, giving reasonable results for the graded buffer layer.