TEM investigation of anisotropic defect structure in cubic GaN/AlGaAs/GaAs(001) grown by MOVPE

Abstract

AbstractThe effects of AlxGa1‐xAs buffer layer insertion on the defect structures and their distribution in cubic (c‐) GaN films on GaAs (001) substrates grown by low‐pressure metalorganic vapor phase epitaxy have been investigated by means of bright‐ and dark‐field cross‐sectional transmission electron microscopy. It is demonstrated that a 300‐nm‐thick Al0.2Ga0.8As buffer layer can protect the GaAs (001) surface from thermal decomposition during the growth at 960 °C, remaining a growth of c‐GaN on GaAs substrate without any voids at the interface. Two different types of defect structures having an anisotropic distribution between the [110] and [1‐10] zone axes were observed. For the [110] zone‐axis, the pyramid‐shaped grains, which are proposed to construct from planar defects, such as SFs and twins, were observed. On the other hand, for the [1‐10] zone‐axis, a dense cubic phase structure with less contribution of planar defects was observed. However, threading dislocations, which were produced by a coalescence of pyramid‐shaped grains in the [110] direction, were observed at the top regions of c‐GaN layer. Both types of defect structures have an anisotropic distribution within a cubic symmetry that may be due to different atomic structures on the AlGaAs surface along the [110] and [1‐10] crystallographic directions. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)