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John O | December 2018

Researchers assess the viability of gallium oxide as an ultrawide bandgap semiconductor

By Josh Perry, Editor


Researchers from the University of Florida, the U.S. Naval Research Laboratory and Korea University have detailed the properties, capabilities, current limitations, and potentials applications for gallium oxide (Ga2O3) as an ultrawide bandgap semiconductor (UWB), according to a report from the American Institute of Physics (AIP).


The pentagon diagram showing the critical material properties important to power semiconductor devices. A larger pentagon is preferred. (AIP Publishing)


Wide bandgap materials, most notably silicon carbide (SiC) and gallium nitride (GaN), have grown in prominence in the electronics industry because of their ability to function at high heat. Gallium oxide has a bandgap of 4.8 electron volts, which is significantly more than the 3.3 eV of SiC or GaN.


“The difference gives Ga2Othe ability to withstand a larger electric field than silicon, SiC and GaN can without breaking down,” the report explained. “Furthermore, Ga2Ohandles the same amount of voltage over a shorter distance. This makes it invaluable for producing smaller, more efficient high-power transistors.”


Researchers indicated that this material has potential in power distribution systems for electric vehicles, converting alternative energy into electricity for the power grid or for building MOSFETs. To make it possible for this material to become common, new thermal management techniques will be required.


The research was recently published in the Journal of Applied Physics. The abstract stated:


“Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics with capabilities beyond existing technologies due to its large bandgap, controllable doping, and the availability of large diameter, relatively inexpensive substrates. These applications include power conditioning systems, including pulsed power for avionics and electric ships, solid-state drivers for heavy electric motors, and advanced power management and control electronics. Wide bandgap (WBG) power devices offer potential savings in both energy and cost.


“However, converters powered by WBG devices require innovation at all levels, entailing changes to system design, circuit architecture, qualification metrics, and even market models. The performance of high voltage rectifiers and enhancement-mode metal-oxide field effect transistors benefits from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. Reverse breakdown voltages of over 2 kV for β-Ga2O3 have been reported, either with or without edge termination and over 3 kV for a lateral field-plated Ga2O3 Schottky diode on sapphire.


“The metal-oxide-semiconductor field-effect transistors fabricated on Ga2O3 to date have predominantly been depletion (d-mode) devices, with a few demonstrations of enhancement (e-mode) operation. While these results are promising, what are the limitations of this technology and what needs to occur for it to play a role alongside the more mature SiC and GaN power device technologies?


“The low thermal conductivity might be mitigated by transferring devices to another substrate or thinning down the substrate and using a heatsink as well as top-side heat extraction. We give a perspective on the materials’ properties and physics of transport, thermal conduction, doping capabilities, and device design that summarizes the current limitations and future areas of development.


“A key requirement is continued interest from military electronics development agencies. The history of the power electronics device field has shown that new technologies appear roughly every 10-12 years, with a cycle of performance evolution and optimization. The older technologies, however, survive long into the marketplace, for various reasons. Ga2O3 may supplement SiC and GaN, but is not expected to replace them.”

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