Surface layer spinodal decomposition in In1−xGaxAsyP1−y and In1−xGaxAs grown by hydride transport vapor-phase epitaxy

Abstract

Composition modulation due to spinodal decomposition in In1−xGaxAsyP1−y quaternary and In1−xGaxAs ternary alloys is observed by transmission electron microscopy in epitaxial layers grown by hydride transport vapor phase epitaxy at 700 °C on (001) InP substrate. A quasi-periodic fine contrast oriented along [100] and [010] directions is found in all samples over a composition range of 0.20≤x≤0.53 and 0.37≤y≤1. Contrary to the result reported on materials grown by liquid-phase epitaxy, complete mixing at composition outside the miscibility gap predicted by thermodynamics for bulk crystals is not observed. The evidence indicates a rapid spinodal decomposition by surface diffusion during vapor phase deposition. Furthermore, transmission electron microscopy diffraction contrast experiments on the (110) cross-sectional view of planar and nonplanar epitaxial layers reveal a columnar structure oriented along the growth direction which is consistent with the surface layer spinodal formation. Additional coarse contrast is observed in InGaAs epilayers. TEM stereo investigation confirms a film thickness variation associated with the coarse contrast.