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Zn XPS spectra for (a) ZnO and (c) ZnO/AlN samples, and Al XPS spectra for (b) AlN and (d) ZnO/AlN samples. Experimental data points are fitted by Voigt (mixed Lorentzian-Gaussian) lineshapes (solid lines) after the application of a Shirley background (dashed line). Also shown are valence band spectra for (e) ZnO and (f) AlN. The peak and VBM positions are summarized in Table I.
The room temperature VBM and conduction band minimum line-up of the ZnO/AlN heterojunction, showing a type-II band alignment. The band line-ups with GaN and InN are also shown. These are derived from the previously determined valence band offsets of the III-Ns (Refs. 11 and 12) and the transitivity rule (Ref. 28) The room temperature band gaps of 3.45 eV for GaN (Ref. 27) and 0.65 eV for InN (Ref. 31) were used to derive the depicted conduction band offsets with ZnO.
Binding energies (in eV) of the XPS peaks and VBM for the ZnO, AlN, and ZnO/AlN samples. Energies are referenced to the Fermi level (0 eV). The errors in the peak positions and VBM are and , respectively.
Valence band offset values (in eV) determined for a ZnO/AlN heterojunction using various combinations of XPS core levels. All values correspond to the VBM of ZnO being below that of AlN. The error in each value is .
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