Formation mechanism of a degenerate thin layer at the interface of a GaN/sapphire system

It has recently been suggested that the thin degenerate layer found at the GaN/sapphire interface results from a high concentration of stacking faults . The studies of this letter, however, show that this is not the most likel y explanation for the presence of such a degenerate layer. Using x-ray ener gy-dispersive spectroscopy and secondary ion-mass spectroscopy, profile dis tributions of elements Ga, N, O, C, and Al, near the interface, have been o btained. The distributions reveal very high O and Al concentrations in the GaN film within 0.2 mu m from the interface, together with a material deple tion of Ga and N. Such conditions strongly favor n(+) conductivity in this interfacial region because not only are N-vacancy and N-site O donors prese nt, but Al incorporated on the Ga sublattice reduces the concentration of c ompensating Ga-vacancy acceptors. The two-layer (film plus interface) condu ction has been modeled, and the effect of conduction in the GaN film thus i solated. (C) 2000 American Institute of Physics. [S0003-6951(00)00302-8].