Direct Determination of Energy Band Alignments of Ni/Al2O3/GaN MOS Structures Using Internal Photoemission Spectroscopy

The energy band alignments of Ni/Al2O3/GaN heterostructures have been explored by internal photoemission (IPE) and capacitance-voltage (CV) measurements. By performing IPE measurements at both reverse- and forward-bias conditions, the Ni/Al2O3 Schottky barrier is found to be 2.9 +/- 0.1 eV with the presence of a strong image force lowering effect, while the Al2O3/GaN conduction-band offset is determined to be 2.2 +/- 0.1 eV and is insensitive to oxide electrical field. CV-based flat-band voltage analysis has further been performed on samples with different oxide thicknesses, not only confirming the IPE-measured band alignment but also revealing the presence of 3.0 x 10(12) cm(-2) net positive charge at the Al2O3/GaN interface.