Thermally grown Nb-oxide for GaN-based MOS-diodes

Abstract

We have grown 10 nm of amorphous Nb2O5 on AlGaN/GaN heterostructure by a combination of sputtering of a thin film of niobium (Nb) followed by rapid thermal annealing in oxygen (O2) ambience. X-ray photoelectron spectroscopy (XPS) analysis shows an ideal stoichiometry of Nb2O5 at annealing temperature 500 °C. The band gap (Eg) and valence band offset with AlGaN (ΔEv) for Nb2O5 are estimated to be 4.15 eV and 0.15 eV, respectively. The root mean square (RMS) roughness of the oxide as measured by atomic force microscopy (AFM) is 1.32 nm. The thickness and crystallinity of the oxide are confirmed by transmission electron microscopy (TEM). The reverse leakage current is observed to reduce by three orders of magnitude for Nb2O5/AlGaN/GaN metal–oxide–semiconductor (MOS) diode as compared to the schottky diode. The dielectric constant of Nb2O5 (εox) and interface density of states (Dit) with AlGaN are estimated to be 58 and 7.0 × 1013 cm−2 eV−1 by capacitance voltage (CV) characteristics, respectively.