Determination of band offsets at the interfaces of NiO and Cr2O3 with InAlN

This work investigates the electronic band alignment of p-NiO/InAlN and p-Cr2O3/InAlN heterostructures for the application of achieving enhancement-mode (e-mode) InAlN-based high-electron-mobility transistors (HEMTs) using x-ray photoelectron spectroscopy (XPS), together with the Kraut method to extract the band alignment parameters from reference oxide films and InAlN HEMT structures. The extracted conduction and valence-band offsets of NiO/InAlN are 1.58 and 2.11 eV, respectively. For Cr2O3/InAlN, the extracted conduction and valence-band offsets are 2.07 and 3.13 eV, respectively. NiO and Cr2O3 thin films were deposited by reactive RF sputtering on metal-organic chemical vapor deposited In0.17Al0.83N HEMT structures grown on sapphire or SiC substrates. The energy bandgap of InAlN and Cr2O3 was determined from XPS energy-loss spectra to be 4.43 and 3.37 eV, respectively, while the energy bandgap of NiO was 3.9 eV, as reported in our previous work. Both heterostructures exhibited staggered type-II band alignment with large interfacial carrier barriers. The large valence-band offsets indicate strong hole confinement and suggest that both oxides are capable of electrostatically depleting the polarization-induced two-dimensional electron gas, thereby facilitating enhancement-mode (E-mode) HEMT operation through a positive threshold-voltage shift. Among the investigated oxides, Cr2O3 exhibited the larger valence- and conduction-band offsets, indicating stronger carrier-blocking capability and suggesting greater potential for suppressing gate leakage and achieving a more positive threshold voltage than the NiO/InAlN heterojunction.