【Member Papers】Gallium oxide (Ga₂O₃) heterogeneous and heterojunction power devices

      Due to its high critical breakdown electrical field and the availability of large-scale single crystal substrates, Gallium oxide (Ga₂O₃) holds great promise for power electronic and radio frequency (RF) applications. While significant advancements have been made in Ga₂O₃ material and device research, there are still challenges related to its ultra-low thermal conductivity and the lack of effective p-type doping methods. These limitations hinder the fabrication of complex device structures and the enhancement of device performance. This review aims to provide an introduction to the research development of Ga₂O₃ heterogeneous and heterojunction power devices based on heterogeneous integration technology. By utilizing ion-cutting and wafer bonding techniques, heterogeneous substrates with high thermal conductivity have been realized, offering a viable solution to overcome the thermal limitations of Ga₂O₃. Compared to Ga₂O₃ bulk devices, Ga₂O₃ devices fabricated on heterogeneous substrates integrated with SiC or Si exhibit superior thermal properties. Power diodes and superjunction transistors based on p-NiO/n-Ga₂O₃ heterojunctions on heterogeneous substrates have demonstrated outstanding electrical characteristics, presenting a feasible method for the development of bipolar devices. The technologies of heterogeneous integration and heterojunction address critical issues related to Ga₂O₃, thereby advancing the commercial applications of Ga₂O₃ devices in power and RF fields. By integrating Ga₂O₃ with other materials and leveraging heterojunction interfaces, researchers and engineers have made significant progress in improving device performance and overcoming limitations. These advancements pave the way for the wider adoption of Ga₂O₃-based devices in various power and RF applications.

Fig. 1. The process flow for transferring β-Ga₂O₃ thin film onto SiC (or Si) by ion cutting. (a)-(b) Implanting H⁺ into bulk β-Ga₂O₃ to form the H-rich layer. (c) Wafer bonding of β-Ga₂O₃ with SiC (or Si), and bonding interfacial layer (IL) can be an amorphous layer or an Al₂O₃ film. (d) Forming plate-like defects by annealing. (e) Splitting. (f) Surface smoothing by ICP etching or CMP. Fabricated GaOSiC is shown.

Fig. 2. Surface blistering of β-Ga₂O₃ bulk wafers through H ion implantation. (a) In situ OM images of the surface variation of H-implanted β-Ga₂O₃ bulk annealed at 480°C, (b) total free energy versus radius of the hydrogen blister with different internal pressures, (c) Arrhenius plot of the blistering time as a function of the annealing temperature, and (d) time for surface blistering versus heating temperature with different values of implantation fluence.

Fig. 3. The XTEM image of β-Ga₂O₃/SiC heterogeneous integration materials based on different bonding methods. （a）surface activated bonding, (b) Hydrophilic bonding.

Paper Link：https://doi.org/10.1016/j.fmre.2023.10.008