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 sub strate by metalorgahic vapor phase epitaxy (MOVPE) using l,l-dimethylh ydrazine (DMHy) and trimethylgallium (TMG) as the sources of nitrogen and gallium, respectively. Before the deposition, the surface of the s ubstrate was nitrided with DMHy. High-resolution images and electron d iffraction patterns confirmed that the GaN films have a zincblende str ucture (beta-GaN) with the lattice constant of a(GaN)=0.454 nm, and co ntain bands of stacking faults parallel to (111) planes. The interface between GaN and GaAs is made of (111) facets with no interlayer. Misf it dislocations are found to be inserted on the interface approximatel y every five atomic planes of GaAs. The nitridation treatment with onl y 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 zincble nde structure during the supply of DMHy and TMG. The formation of face ts on the top surface of GaN and on the interface of GaN/GaAs is expla ined in terms of the diffusion of arsenic in beta-GaN. The characteris tics of the structure of GaN films grown at 600 and 650 degrees C are also presented.