RHEED patterns of the initial stages of the GaN deposition on the Sc2O3/Y2O3 buffer. Images were taken in-situ at substrate temperature along Sc2O3 [ 10] (GaN[11 0]) direction. Arrows in the RHEED pattern recorded after 120 s indicate reflections associated with cubic GaN inclusions.
(a) RHEED image line spacing W/2 as a function of the GaN deposition time, (b) GaN crystal structure viewed along [11 0] direction, (c)Sc2O3 crystal structure viewed along [ 10].
Sc 2p and N 1s XPS spectra taken after 0, 10, 30, 60, and 360 s of the GaN growth.
(a) Attenuation curve of the Sc XPS line and (b) Sc2O3 surface coverage by the GaN islands as a function of the GaN deposition time. (c)AFM image of the GaN surface after 240 s of growth.
Evolution of the Ga peak upon GaN growth.
Integrated peak areas of the Ga N-Ga-O-Sc, Ga N-Ga-N, and N 1s signals plotted as a function of GaN growth time
Sketch of the GaN/Sc2O3 interface model (a) cross section viewed along Sc2O3 [ ] direction and (b) top view. Here, nitride is stretched by 4.4% and the oxide is compressed by 4.4% to match Ga and O atoms. In the NI model, the oxygen vacancies in Sc2O3 are filled with nitrogen atoms.
Interface models. Only bonds are shown. (a) Interface with nitrogen interstitials: NI model. The outer surface of the nitride is saturated with pseudo-hydrogen atoms (blue bonds) to simulate a thick film. (b) The same as in (a), but without the pseudo-hydrogen atoms; this is a “true” thin film. (c) Interface without nitrogen interstitials: OV model. The thin film version is shown (no termination of the outer surface by pseudo-hydrogen atoms). (d) Energy of the interfacial nitrogen for a thin film (blue dashed line) and for a thick film (red solid line), as a function of N chemical potential. The chemical potential varies from Ga-rich regime (on the left, equilibrium with Ga atom) to N-rich regime (on the right, equilibrium with N2 ) condition. The energy plotted is equal to the energy difference between the NI and OV structures, per N atom. ΔH f GaN : experimental, as quoted by Fuchs et al. 31
Properties of wurtzite and zinc blende GaN.
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