Gallium oxide (Ga2O3) heterogeneous and heterojunction power devices

Abstract

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.

Keywords: Ga2O3; Heterogeneous integration; Heterojunction; NiO; Superjunction.

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 . © [2021] IEEE. Reprinted, with permission, from .

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. Adapted with permission from . Copyright 2021, American Chemical Society.

Fig. 3

The XTEM image of β-Ga₂O₃/SiC heterogeneous integration materials based on different bonding methods. (a) surface activated bonding , (b) Hydrophilic bonding . Reprinted from , with the permission of AIP Publishing.

Fig. 4

A 2-inch single-crystalline Ga₂O₃ thin film transferred onto Si and SiC substrates. (a) The photograph of a 2-inch β-Ga₂O₃ thin film transferred onto SiC handle wafer and the exfoliated β-Ga₂O₃ bulk wafer, (b) the thickness mapping of the β-Ga₂O₃ thin film , Panels (a) and (b) adapted with permission from . Copyright 2021, American Chemical Society. (c) the normalized ($\overline{2}01$) XRCs of the β-Ga₂O₃ thin film before and after a post-annealing process, (d) AFM image of the β-Ga₂O₃ thin film after CMP process .

Fig. 5

Ga₂O₃ heterogeneous SBDs. (a) The optical image of fabricated β-Ga₂O₃/TiN SBD and device structure . (b) Temperature-dependent I-V characteristics of the β-Ga₂O₃/TiN SBD with a stable I_ON/I_OFF ratio. Panels (a) and (b) reproduced with permission from . Copyright 2020, IOP Publishing Ltd. (c) Cross-sectional TEM microscope image of Ga₂O₃/Si interface and the EDS spectrum of Ga, O and Si at the interface . (d) Comparison of R_on,sp,d and R_on,sp,l of Ga₂O₃/Si SBDs with different Mole Fraction (MF). (e) comparison of R_on,sp,d and R_on,sp,l of Ga₂O₃/Si SBDs with different amorphous layer thickness (T_ox).

Fig. 6

Ga₂O₃ heterogeneous MOSFETs. (a) Schematics of the heterogeneous Ga₂O₃ MOSFETs fabricated on the heterogeneous wafers . (b) The transfer characteristics of an E-mode GaOSiC MOSFET with a T_ch of ∼40 nm. (c) Transfer characteristics of a GaOISiC MOSFET measured at different ambient temperatures (T_amb). © [2021] IEEE. Panels (a), (b) and (c) Reprinted, with permission, from . (d) Schematic of the heterogeneous GaOISi MOSFET . (e) Transfer characteristics of a D-mode GaOISi MOSFET measured at different temperatures. (f) Dependence of I_ON and I_OFF on the temperature. Panels (d), (e) and (f) Reproduced with permission from Springer Nature, copyright 2020. (g) Schematic of the recessed-gate GaOSiC MOSFET . (h) Temperature dependence of R_ON and drive current of the recessed-gate GaOSiC MOSFET. (i) The evolution of transfer length at the electrode contacts with the temperature. © [2022] IEEE. Panels (g), (h) and (i) Reprinted, with permission, from .

Fig. 7

Channel mobility properties of Ga₂O₃ heterogeneous MOSFETs. (a) The transfer characteristics of the GaOISi MOSFETs with different channel thickness . © [2021] IEEE. Reprinted, with permission, from . (b) Calculated µ_eff vs Q_ch for GaOISi MOSFETs with the different channel thickness. Benchmarking µ_eff of (c) GaOISi and (d) GaOSiC MOSFETs with the reported µ_H and µ_eff of β-Ga₂O₃ materials and devices ,. (e) Calculated µ_FE for the accumulated GaOSiC MOSFET as T_amb increases from 0 °C to 150 °C . © [2021] IEEE. Reprinted, with permission, from .

Fig. 8

NiO/Ga₂O₃ heterojunction power diode. Schematic cross-section of (a) double-layered and (b) single-layered NiO/Ga₂O₃ HJD. (c) Breakdown characteristics of HJD in (a) and (b) . Reprinted from , with the permission of AIP Publishing. (d) NiO/Ga₂O₃ heterojunction with beveled mesa . (e) Simulated electric field distributions of NiO/Ga₂O₃ HJD with varying bevel angle. (f) Reverse I-V characteristics . © [2022] IEEE. Reprinted, with permission, from .

Fig. 9

NiO/Ga₂O₃ HJBS diodes. (a) Schematic cross-section of NiO/Ga₂O₃ HJBS with FLRs. (b) Top-view microscopy image. (c) Semi-logarithmic J-V characteristics. (d) Linear J–V characteristics and extracted R_on,sp as a function of forward bias. (e) Reverse J-V characteristics. Reprinted from , with the permission of AIP Publishing.

Fig. 10

Dynamic electrical characteristics of NiO/Ga₂O₃ heterojunction power diodes. (a) Reverse recovery characteristics and (b) Surge current characteristics of the 9-mm² HJD and SBD . © [2021] IEEE. Reprinted, with permission, from . (c) Corresponding surge power and energy. (d) The UIS current and voltage waveforms of the HJD. (e) Repetitive UIS characteristics . (f) System efficiency vs. output power of a 500-W PFC circuit at a switching frequency of 0.1 MHz and 0.5 MHz . © [2022] IEEE. Reprinted, with permission, from .

Fig. 11

Ga₂O₃ based SJ-MOSFET,. Schematic cross-section of (a) SJ-MOSFET. (b) Reverse J-V characteristics. © [2021] IEEE. Reprinted, with permission, from ,.