Temperature Dependence of Ultrathin Mixed-Phase Ga₂O₃Films Grown on the α-Al₂O₃Substrate via Mist-CVD

Abstract

Alpha (α)- and beta (β)-phase gallium oxide (Ga2O3), emerging as ultrawide-band gap semiconductors, have been paid a great deal of attention in optoelectronics and high-performance power semiconductor devices owing to their ultrawide band gap ranging from 4.4 to 5.3 eV. The hot-wall mist chemical vapor deposition (mist-CVD) method has been shown to be effective for the growth of pure α- and β-phase Ga2O3 thin films on the α-Al2O3 substrate. However, challenges to preserve their intrinsic properties at a critical growth temperature for robust applications still remain a concern. Here, we report a convenient route to grow a mixed α- and β-phase Ga2O3 ultrathin film on the α-Al2O3 substrate via mist-CVD using a mixture of the gallium precursor and oxygen gas at growth temperatures, ranging from 470 to 700 °C. The influence of growth temperature on the film characteristics was systematically investigated. The results revealed that the as-grown Ga2O3 film possesses a mixed α- and β-phase with an average value of dislocation density of 1010 cm–2 for all growth temperatures, indicating a high lattice mismatch between the film and the substrate. At 600 °C, the ultrathin and smooth Ga2O3 film exhibited a good surface roughness of 1.84 nm and an excellent optical band gap of 5.2 eV. The results here suggest that the mixed α- and β-phase Ga2O3 ultrathin film can have great potential in developing future high-power electronic devices.

Heteroepitaxial Growth of an Ultrathin β-Ga2O3 Film on a Sapphire Substrate Using Mist CVD with Fluid Flow Modeling

“…In Figure b, TEM images show the ultrathin Ga 2 O 3 film obtained in 5 to 6 nm with a growth rate of 0.041 nm/min. Our previous study showed the 20 nm thin mixed-phase Ga 2 O 3 film grown on the sapphire substrate at 470 to 600 °C . In this study, we achieved an ultrathin (5 nm) film of the pure β phase at 700 °C, but this phase transition does not correlate with thickness.…”

“…Our previous study showed the 20 nm thin mixed-phase Ga 2 O 3 film grown on the sapphire substrate at 470 to 600 °C. 28 In this study, we achieved an ultrathin (5 nm) film of the pure β phase at 700 °C, but this phase transition does not correlate with thickness. This indicates that the growth rate is much slower in this mist CVD growth process.…”

“…It is a widely used substrate to grow high-quality heteroepitaxial α-Ga 2 O 3 via the mist CVD method for commercializing power device applications. Mist CVD is very popular for growing the α phase than β-Ga 2 O 3 on the c -plane sapphire substrate. − It is difficult to develop a very uniform and high-quality β phase due to the significantly large lattice mismatch (6.6%) between β-Ga 2 O 3 and the sapphire substrate . Hence, there is a lack of substantial studies on mist CVD-grown heteroepitaxial β-Ga 2 O 3 films grown on the c -plane sapphire substrate at this particular growth temperature.…”

Characteristics of Vertical Ga2O3 Schottky Junctions with the Interfacial Hexagonal Boron Nitride Film

“…Gallium oxide (Ga 2 O 3 ) with an ultrawide band gap (UWBG) has piqued the interest of researchers working on deep ultraviolet (UV) photonics and next-generation power electronic devices. − Semiconductors based on UWBG Ga 2 O 3 materials can withstand much higher critical electric fields (6–8 MV/cm) before avalanche breakdown than silicon- (Si), silicon carbide- (SiC), and gallium nitride (GaN)-based devices. ,, Furthermore, Baliga’s figure of merit presents the advantage of Ga 2 O 3 for power switching applications over the Si (3000×), SiC (10×), and GaN (4×). , It has been demonstrated that high-quality single-crystal Ga 2 O 3 can be synthesized using melt growth techniques such as Czochralski, floating zone, and edge-defined film-fed growth (EFG). − In addition, halide vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), and chemical vapor deposition (CVD) methods for growing high-quality Ga 2 O 3 have been developed. − Johnson’s figure of merit (JFOM/power–frequency product) of Ga 2 O 3 (3× of GaN) , illustrates the potential benefit of using Ga 2 O 3 in radio frequency (RF) devices. Chabak et al have reported on the fabrication of the Ga 2 O 3 MOSFET device using a thin and highly doped channel and achieving a drain-source current of 275 mA/mm at a drain to source bias of 10 V for that exhibited record-high f t / f max = 5.1/17.1 GHz .…”

“…The heterojunction and Schottky junction-based β-Ga 2 O 3 devices are of great interest for the development of high-voltage devices and solar-blind UV photodetectors, considering the intrinsic n-type conductivity of β-Ga 2 O 3 in the presence of unintentional dopants. − The conventional Ga 2 O 3 Schottky junction devices were studied with metal electrodes such as Au, Pt, and Ni, taking into account the metals’ appropriate work function. , Again, studies on metal–insulator–semiconductor (MIS)-based SBD devices have been conducted, owing to the benefit of lowering the reverse saturation current. − The MIS-based SBD devices have been fabricated using insulating dielectric materials, such as SiO 2 , Si 3 N 4 , Al 2 O 3, and so forth. − , The thermal stability of Ga 2 O 3 Schottky contacts is also an important aspect, for which materials with high melting temperatures and low reactivity with Ga 2 O 3 are of significant interest . Furthermore, controlling near-surface ion damage during sputtering deposition of a barrier layer/insulating dielectric , is required.…”