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

As the p-type doping <inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga<sub>2</sub>O<sub>3</sub> is absent up to now, metal gate (MG) stacks with high work functions are expected to benefit the fabrication of normally- OFF <inline-formula> <tex-math notation="LaTeX">$\beta$ </tex-math></inline-formula>-Ga<sub>2</sub>O<sub>3</sub> transistors. In this article, the electrical characteristics of <inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga<sub>2</sub>O<sub>3</sub> 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 (<inline-formula> <tex-math notation="LaTeX">${D}_{\text {it}}$ </tex-math></inline-formula>) of HfAlO/<inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga<sub>2</sub>O<sub>3</sub> interface is characterized based on the frequency-dependent capacitance–voltage (<inline-formula> <tex-math notation="LaTeX">${C}{-}{V}$ </tex-math></inline-formula>) and photo-assisted deep ultraviolet (DUV) <inline-formula> <tex-math notation="LaTeX">${C}{-}{V}$ </tex-math></inline-formula> measurements. An average <inline-formula> <tex-math notation="LaTeX">$D_{\text {it}}$ </tex-math></inline-formula> of <inline-formula> <tex-math notation="LaTeX">${4.45}\times {10}^{{11}}$ </tex-math></inline-formula> eV<inline-formula> <tex-math notation="LaTeX">$^{-{1}}$ </tex-math></inline-formula>cm<inline-formula> <tex-math notation="LaTeX">$^{-{2}}$ </tex-math></inline-formula> is extracted from the photo-assisted (deep UV) <inline-formula> <tex-math notation="LaTeX">${C}{-}{V}$ </tex-math></inline-formula> measurement, while a large amount of border traps, negative fixed charges, and deep traps is also induced at the oxide layer and/or HfAlO/<inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga<sub>2</sub>O<sub>3</sub> interface. Then, this article investigates the evaluations of Ti, Ni, Au, and Pt as candidate MGs for <inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga<sub>2</sub>O<sub>3</sub> MOS using Al-rich HfAlO as gate dielectric. The obvious flat-band voltage (<inline-formula> <tex-math notation="LaTeX">$V_{\text {FB}}$ </tex-math></inline-formula>) shift and gate leakage variation are observed in <inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga<sub>2</sub>O<sub>3</sub> 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 <inline-formula> <tex-math notation="LaTeX">$\beta$ </tex-math></inline-formula>-Ga<sub>2</sub>O<sub>3</sub> transistors, while Ti electrode is more suitable for normally- ON <inline-formula> <tex-math notation="LaTeX">$\beta$ </tex-math></inline-formula>-Ga<sub>2</sub>O<sub>3</sub> transistors. This article provides an additional practical guideline for choosing the appropriate MG stacks and potential gate dielectric to the development of normally-OFF Ga<sub>2</sub>O<sub>3</sub> transistors.