Ultrawide Band Gap β-Ga₂O₃ Nanomechanical Resonators with Spatially Visualized Multimode Motion

Beta gallium oxide (β-Ga₂O₃) is an emerging ultrawide band gap (4.5 eV-4.9 eV) semiconductor with attractive properties for future power electronics, optoelectronics, and sensors for detecting gases and ultraviolet radiation. β-Ga₂O₃ thin films made by various methods are being actively studied toward such devices. Here, we report on the experimental demonstration of single-crystal β-Ga₂O₃ nanomechanical resonators using β-Ga₂O₃ nanoflakes grown via low-pressure chemical vapor deposition (LPCVD). By investigating β-Ga₂O₃ circular drumhead structures, we demonstrate multimode nanoresonators up to the sixth mode in high and very high frequency (HF/VHF) bands, and also realize spatial mapping and visualization of the multimode motion. These measurements reveal a Young's modulus of E_Y = 261 GPa and anisotropic biaxial built-in tension of 37.5 MPa and 107.5 MPa. We find that thermal annealing can considerably improve the resonance characteristics, including ∼40% upshift in frequency and ∼90% enhancement in quality (Q) factor. This study lays a foundation for future exploration and development of mechanically coupled and tunable β-Ga₂O₃ electronic, optoelectronic, and physical sensing devices.