Transmission electron microscopic and X-ray diffraction measurements revealed the presence of stacking faults in undoped cubic thin layers. The importance of defects in the interfacial region of the films was demonstrated by showing that the stacking faults acted as nucleation sites for precipitates of residual impurities (such as C and Si) which were present in GaN layers grown onto SiC(001) substrates. The imaging secondary ion mass spectroscopic technique was used to locate the impurities. A systematic decrease in the stacking-fault density as a function of the layer thickness was explained in terms of an annihilation mechanism. The effects of the usual dopants upon the structural properties of GaN layers were studied, and it was shown that Mg had a tendency to leave the Ga sites by forming Mg precipitates at a concentration of more than 1019/cm3; contrary to the results found for heavily Si-doped layers.

Structural Properties of Undoped and Doped Cubic GaN Grown on SiC(001). E.Martinez-Guerrero, E.Bellet-Amalric, L.Martinet, G.Feuillet, B.Daudin, H.Mariette, P.Holliger, C.Dubois, C.Bru-Chevallier, P.A.Nze, T.Chassagne, G.Ferro, Y.Monteil: Journal of Applied Physics, 2002, 91[8], 4983-7