Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (e) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.

A review of Ga2O3 materials, processing, and devices

A new platform described as the liquid metal/metal oxide (LM/MO) framework is introduced. The constituent spherical structures of these frameworks are made of micro- to nanosized liquid metal spheres and nanosized metal oxides, combining the advantages of both materials. It is shown that the diameters of the spheres and the stoichiometry of the structures can be actively controlled. Additionally, the liquid suspension of these spheres demonstrates tuneable plasmon resonances. These spherical structures are assembled to form LM/MO frameworks which are capable of demonstrating high sensitivity towards low concentrations of heavy metal ions, and enhanced solar light driven photocalalytic activities. These demonstrations imply that the LM/MO frameworks are a suitable candidate for the development of future high performance electronic and optical devices.

Liquid Metal/Metal Oxide Frameworks

Review of polymorphous Ga2O3 materials and their solar-blind photodetector applications

In this paper, β-Ga
 2
O
 3
 ultraviolet photodetectors were grown on sapphire utilizing the laser molecular beam epitaxy tool. The impact of oxygen pressure P
 O2
 in growth chamber on the crystal quality, the surface morphology, the chemical component of Ga
 2
O
 3
 films, and the electrical performance of photodetectors are characterized. As the P
 O2
 is increased during growth, the concentration of oxygen vacancy (V
 O
) is effectively reduced. The photodetector grown at the P
 O2
 of 0.05 mbar exhibits the significantly improved photocurrent I
 photo
 and responsivity R characteristics in comparison with the device grown with the P
 O2
 of 0.01 mbar, which is attributed to a reduction in the number of V
 O
. However, as the P
 O2
 continuously increased to 0.09 mbar, I
 photo
 and R of the detector are degraded, which might be due to the fact that the gallium vacancies (V
 Ga
), as the dominant trapping centers, lead to the recombination of photo-generated carriers.

L. Binet

Papers

Characterization of oxygen deficient gallium oxide films grown by PLD