Al 2O 3 films, HfO 2 films, and HfO 2/Al 2O 3 stacked structures were deposited on n-type, Ga-face, GaN wafers using plasma-enhanced atomic layer deposition (PEALD). The wafers were first treated with a wet-chemical clean to remove organics and an in-situ combined H 2/N 2 plasma at 650°C to remove residual carbon contamination, resulting in a clean, oxygen-terminated surface. This cleaning process produced slightly upward band bending of 0.1 eV. Additional 650°C annealing after plasma cleaning increased the upward band bending by 0.2 eV. After the initial clean, high-k oxide films were deposited using oxygen PEALD at 140°C. The valence band and conduction band offsets (VBOs and CBOs) of the Al 2O 3/GaN and HfO 2/GaN structures were deduced from in-situ x-ray and ultraviolet photoemission spectroscopy (XPS and UPS). The valence band offsets were determined to be 1.8 and 1.4 eV, while the deduced conduction band offsets were 1.3 and 1.0 eV, respectively. These values are compared with the theoretical calculations based on the electron affinity model and charge neutrality level model. Moreover, subsequent annealing had little effect on these offsets; however, the GaN band bending did change depending on the annealing and processing. An Al 2O 3 layer was investigated as an interfacial passivation layer (IPL), which, as results suggest, may lead to improved stability, performance, and reliability of HfO 2/IPL/GaN structures. The VBOs were ∼0.1 and 1.3 eV, while the deduced CBOs were 0.6 and 1.1 eV for HfO 2 with respect to Al 2O 3 and GaN, respectively.
ASJC Scopus subject areas
- Physics and Astronomy(all)