α-Gallium Oxide Films on Microcavity-Embedded Sapphire Substrates Grown by Mist Chemical Vapor Deposition for High-Breakdown Voltage Schottky Diodes

Abstract

α-Gallium oxide, with its large band gap energy, is a promising material for utilization in power devices. Sapphire, which has the same crystal structure as α-Ga 2 O 3 , has been used as a substrate for α-Ga 2 O 3 epitaxial growth. However, lattice and thermal expansion coefficient mismatches generate a high density of threading dislocations (TDs) and cracks in films. Here, we demonstrated the growth of α-Ga 2 O 3 films with reduced TD density and residual stress on microcavity-embedded sapphire substrates (MESS). We fabricated the two types of substrates with microcavities: diameters of 1.5 and 2.2 μm, respectively. We confirmed that round conical-shaped cavities with smaller diameters are beneficial for the lateral overgrowth of α-Ga 2 O 3 crystals with lower TD densities by mist chemical vapor deposition. We could obtain crack-free high-crystallinity α-Ga 2 O 3 films on MESS, while the direct growth on a bare sapphire substrate resulted in an α-Ga 2 O 3 film with a number of cracks. TD densities of α-Ga 2 O 3 films on MESS with 1.5 and 2.2 μm cavities were measured to be 1.77 and 6.47 × 10 8 cm −2 , respectively. Furthermore, cavities in MESS were certified to mitigate the residual stress via the redshifted Raman peaks of α-Ga 2 O 3 films. Finally, we fabricated Schottky diodes based on α-Ga 2 O 3 films grown on MESS with 1.5 and 2.2 μm cavities, which exhibited high breakdown voltages of 679 and 532 V, respectively. This research paves the way to fabricating Schottky diodes with high breakdown voltages based on high-quality α-Ga 2 O 3 films.

Gallium Oxide Nanostructures: A Review of Synthesis, Properties and Applications

“…This is a low scale technique, which is done in ambient conditions. It is an easier technique and it has often been reported regarding α-Ga 2 O 3 structure [53,125,126]. There have been several authors who have used this for beta gallium oxide growth as well [127,128].…”

Demonstration of thick phase-pure β-Ga2O3 on a c-plane sapphire substrate using MOCVD

“…In κ-Ga2O3, the orthorhombic domains are rotated 120° against each other forming a pseudo-hexagonal structure and often called ε-Ga2O3 [8], thus, ε-Ga2O3 and κ-Ga2O3 terms are used interchangeably to refer to orthorhombic Ga2O3 in literature. The fabrication and operation of Schottky diodes and MESFETs were also demonstrated with α-Ga2O3 and ε-Ga2O3 [9]- [11]. However, the metastable αand ε-Ga2O3 phases convert to more stable β-Ga2O3 at high temperatures [12].…”

Interfacial Properties of the SnO/κ-Ga2O3 p-n Heterojunction: A Case of Subsurface Doping Density Reduction via Thermal Treatment in κ-Ga2O3

“…Therefore, bulk single crystals may be produced by melt growth techniques such as Czochralski (CZ), floating zone (FZ), vertical Bridgman, and edge-defined film-fed growth (EFG), which paves the way to production of high-quality substrates − as well as to homoepitaxy. Many growth methods are available for epitaxial growth of Ga 2 O 3 polymorphs such as metal–organic chemical vapor deposition (MOCVD), , magnetron sputtering, , mist-chemical vapor deposition (Mist-CVD), , atomic layer deposition (ALD), , pulsed laser deposition (PLD), halide vapor phase epitaxy, and molecular beam epitaxy (MBE). , In spite of the numerous merits of the β-Ga 2 O 3 , there are concerns regarding its anisotropic thermal conductivity and easiness of cleavage. ,, κ-Ga 2 O 3 is the second most stable polymorph, and its orthorhombic cell has higher symmetry with respect to the monoclinic one, which may lead to easier epitaxial growth and novel heterostructures. , Furthermore, it exhibits a spontaneous polarization along the [001] direction of the orthorhombic cell that could help to obtain high-density two-dimensional electron gases (2DEG) at the interface of κ-Ga 2 O 3 based heterostructures, , and thus a conducting channel for high-mobility field effect transistors, which is becoming one of the most intriguing topics of the literature on Ga 2 O 3 . Recently, κ-Ga 2 O 3 , was employed for fabrication of planar diodes and solar-blind UV–C photodetectors .…”