17 - Power MOSFETs and diodes

Abstract

Gallium oxide possesses material properties that are advantageous for power electronic devices. Combined with the availability of native Ga2O3 substrates, Ga2O3-based devices are projected to supplant Si-based as well as GaN- and SiC-based power electronics over a certain slice of the high-voltage, low-frequency application space. The β-type of Ga2O3 is clearly the most developed polymorph of Ga2O3. Devices based on β-Ga2O3 have not reached below the expected 8MV/cm theoretical value for breakdown voltage. The best Schottky barrier diodes based on β-Ga2O3 have achieved a breakdown strength of only approximately 1MV/cm. Recent results in Schottky diodes fabricated from 0.43μm mist grown α-Ga2O3 displayed a breakdown strength of 12MV/cm. For transistors, a 3.8-MV/cm breakdown strength was obtained for a 0.65-μm channel length device. The best reported breakdown voltage of 755V only corresponds to 0.5MV/cm breakdown strength that was obtained for a 15-μm channel length device. As material quality improves, it is expected that the experimental breakdown voltages will approach the theoretical predictions. A clear research path is that large-area and vertical devices will mirror the designs of silicon and silicon carbide power devices particularly with an emphasis on vertical design with defined conduction paths. The relatively low thermal conductivity of Ga2O3 creates self-heating effects that must be mitigated in order to utilize Ga2O3 for high-power at even moderate switching frequencies. Lastly, the current state of p-type β-Ga2O3 is currently an issue to utilized pn junctions to define the current path in vertical devices. This issue, like many aspects of Ga2O3, is rapidly evolving.