Band offsets of polar and nonpolar GaN/ZnO heterostructures determined by synchrotron radiation photoemission spectroscopy

C-plane (polar) and m-plane (nonpolar) GaN/ZnO heterostructures have been fabricated by pulsed laser deposition at room temperature, and their electronic structures have been characterized by synchrotron radiation photoemission spectroscopy. Based on the binding energies of core levels and valence band maximum values, the valence band offsets have been found to be 0.7 +/- 0.1 and 0.9 +/- 0.1 eV for polar and nonpolar GaN/ZnO heterojunctions, respectively. Both heterostructures show typeII band configurations with conduction band offsets of 0.8 +/- 0.1 and 1.0 +/- 0.1 eV, respectively. GaN and ZnO show upward and downward band bending toward the interface in the nonpolar GaN/ZnO heterojunction. However, both GaN and ZnO show upward band bending toward the interface in the polar heterojunction, which is attributed to negative charges. Analysis of N 1s spectra has revealed that N-O bonds exist only at the polar interface, which probably caused the formation of the negative charges. (c) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim