Influence of Metal Gate Electrodes on Electrical Properties of Atomic-Layer-Deposited Al-Rich HfAlO/Ga2O3 MOSCAPs

As the p-type doping $\beta $ -Ga2O3 is absent up to now, metal gate (MG) stacks with high work functions are expected to benefit the fabrication of normally- OFF $\beta$ -Ga2O3 transistors. In this article, the electrical characteristics of $\beta $ -Ga2O3 metal-electrode-gated metal–oxide–semiconductor (MOS) devices with Al-rich HfAlO dielectrics and different MG stacks (Ni, Au, Pt, and Ti) are evaluated. The interface state density ( ${D}_{\text {it}}$ ) of HfAlO/ $\beta $ -Ga2O3 interface is characterized based on the frequency-dependent capacitance–voltage ( ${C}{-}{V}$ ) and photo-assisted deep ultraviolet (DUV) ${C}{-}{V}$ measurements. An average $D_{\text {it}}$ of ${4.45}\times {10}^{{11}}$ eV $^{-{1}}$ cm $^{-{2}}$ is extracted from the photo-assisted (deep UV) ${C}{-}{V}$ measurement, while a large amount of border traps, negative fixed charges, and deep traps is also induced at the oxide layer and/or HfAlO/ $\beta $ -Ga2O3 interface. Then, this article investigates the evaluations of Ti, Ni, Au, and Pt as candidate MGs for $\beta $ -Ga2O3 MOS using Al-rich HfAlO as gate dielectric. The obvious flat-band voltage ( $V_{\text {FB}}$ ) shift and gate leakage variation are observed in $\beta $ -Ga2O3 capacitors with different MG solutions, indicating that HfAlO dielectric combined with Ni, Au, and Pt MGs is promising to facilitate some beneficial modifications of normally- OFF $\beta$ -Ga2O3 transistors, while Ti electrode is more suitable for normally- ON $\beta$ -Ga2O3 transistors. This article provides an additional practical guideline for choosing the appropriate MG stacks and potential gate dielectric to the development of normally-OFF Ga2O3 transistors.