Nanowire-Seeded Growth of Single-Crystalline (010) β-Ga₂ O₃ Nanosheets with High Field-Effect Electron Mobility and On/Off Current Ratio

2D β-Ga₂ O₃ nanosheets, as fundamental materials, have great potential in next generations of ultraviolet transparent electrodes, high-temperature gas sensors, solar-blind photodetectors, and power devices, while their synthesis and growth with high crystalline quality and well-controlled orientation have not been reported yet. The present study demonstrates how to grow single-crystalline ultrathin quasi-hexagonal β-Ga₂ O₃ nanosheets with nanowire seeds and proposes a hierarchy-oriented growth mechanism. The hierarchy-oriented growth is initiated by epitaxial growth of a single-crystalline $\left(\stackrel{-}{2}01\right)$ β-Ga₂ O₃ nanowire on a GaN nanocrystal and followed by homoepitaxial growth of quasi-hexagonal (010) β-Ga₂ O₃ nanosheets. The undoped 2D (010) β-Ga₂ O₃ nanosheet field effect transistor has a field-effect electron mobility of 38 cm² V^-1 s^-1 and an on/off current ratio of 10⁷ with an average subthreshold swing of 150 mV dec^-1 . The from-nanowires-to-nanosheets technique paves a novel way to fabricate nanosheets, which has great impact on the field of nanomaterial synthesis and growth and the area of nanoelectronics as well.