Strain relaxation and surface roughness of In_xAl_(1-x)As graded buffer layers grown on InP for 6.05 A applications

摘要

In this study, metamorphic compositionally graded In_xAl_(1-x)As layers grown on InP by molecular beam epitaxy with a final indium mole fraction of x=1.0 (6.05 A) are investigated. To examine the effects of relative growth temperature on strain relaxation and surface morphology at different stages of the buffer layer growth, a series of samples was produced with the indium mole fraction graded from x=0.52 to x=0.64, 0.79, and 1.0 with a constant grading rate. The high misfit dislocation velocity in this system allows the grading to be accomplished with a thin layer (～1μm), complete strain relaxation and low threading dislocation densities. The evolution of the strain relaxation, threading dislocation density, and surface morphology were evaluated by triple axis x-ray diffraction, transmission electron microscopy (TEM), etch pit density (EPD), and atomic force microscopy. Higher growth temperature led to threading densities as low as 10~6 cm~(-2), as measured by plan-view TEM and EPD. The final surface roughness was controlled by the growth temperature of a constant composition cap layer.