TRANSMISSION ELECTRON-MICROSCOPE OBSERVATION OF CUBIC GAN GROWN BY METALORGANIC VAPOR-PHASE EPITAXY WITH DIMETHYLHYDRAZINE ON (001) GAAS

Cross-sectional transmission electron microscope observation has been performed on the microstructure of GaN films grown on a (001) GaAs substrate by metalorgahic vapor phase epitaxy (MOVPE) using l,l-dimethylhydrazine (DMHy) and trimethylgallium (TMG) as the sources of nitrogen and gallium, respectively. Before the deposition, the surface of the substrate was nitrided with DMHy. High-resolution images and electron diffraction patterns confirmed that the GaN films have a zincblende structure (beta-GaN) with the lattice constant of a(GaN)=0.454 nm, and contain bands of stacking faults parallel to (111) planes. The interface between GaN and GaAs is made of (111) facets with no interlayer. Misfit dislocations are found to be inserted on the interface approximately every five atomic planes of GaAs. The nitridation treatment with only DMHy for 130 min is found to form a thick layer of beta-GaN on the (001) GaAs substrate. Nuclei of beta-GaN formed by the pretreatment of surface nitridation play an important role in growing GaN in a zincblende structure during the supply of DMHy and TMG. The formation of facets on the top surface of GaN and on the interface of GaN/GaAs is explained in terms of the diffusion of arsenic in beta-GaN. The characteristics of the structure of GaN films grown at 600 and 650 degrees C are also presented.