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

As the p-type doping β-Ga
₂
O
₃
is absent up to now, metal gate (MG) stacks with high work functions are expected to benefit the fabrication of normally-OFF β-Ga
₂
O
₃
transistors. In this article, the electrical characteristics of β-Ga
₂
O
₃
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 (Dit) of HfAlO/β-Ga
₂
O
₃
interface is characterized based on the frequency-dependent capacitance-voltage (C-V) and photo-assisted deep ultraviolet (DUV) C-V measurements. An average Dit of 4.45 × 1011 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/β-Ga
₂
O
₃
interface. Then, this article investigates the evaluations of Ti, Ni, Au, and Pt as candidate MGs for β-Ga
₂
O
₃
MOS using Al-rich HfAlO as gate dielectric. The obvious flat-band voltage (VFB) shift and gate leakage variation are observed in β-Ga
₂
O
₃
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 β-Ga
₂
O
₃
transistors, while Ti electrode is more suitable for normally-ON β-Ga
₂
O
₃
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
₂
O
₃
transistors.