Cornell researchers recently announced the development of a new diode based on gallium nitride. The payoff is that it has some stellar specifications!
The diode has an exceptionally high breakdown voltage (BV) because of the material's high bandgap. It also has high electron mobility that allows a very low on resistance (Ron), which caters to a lower forward voltage drop which pays big dividends in efficiency.
The higher the efficiency, the higher the current a device can handle before self-heating puts the brakes on. This means that really big power devices can be built, but it also means much smaller devices can be used to handle conventional loads.
The novel diode has a BV just over 1.4kV. This could allow high voltage power devices to be integrated into smaller applications like hand tools or servo applications.
The expression of the device's power ability is given by a figure-of-merit watt-density calculated using the breakdown voltage and the differential on-resistance, which for this new diode is 0.12mΩcm2 (with a mesa diameter of 107µm), resulting in ~16.5GW/cm2!
That is the highest ever demonstrated by any semiconductor.
The ideality factor is used to describe how closely diodes adhere to the ideal diode equation that haunted EEs in college. The ideal diode expects all recombination to occur in the bulk areas of the diode and not in the junctions. A diode can fall short of this ideal because of various failings including defects in the atomic lattices it's constructed from. An ideality factor of 1 would describe a perfect diode. Typical diodes range higher than 2, and some up to 4. This gallium nitride diode, however, sports an ideality factor of 1.1.
A lot of focus was put on making the bulk substrate of this diode very low defect, and the low ideality is the reward. The diode was grown epitaxially using metalorganic chemical vapor deposition (MOCVD) on a bulk GaN substrate.
The GaN diode's high efficiency could save lots of energy in applications such as server farms. The possibilities are of potential national importance, which is why the U.S. Department of Energy's Advanced Research Projects Agency is underwriting a substantial amount of the research.
If more efficient semiconductors can provide a 10~20% efficiency enhancement, as is expected, consider how this improves the national power picture. You could get more use from your generated power, or reduce the amount that you need to generate.
The diode is only the physics first step in GaN transistor development.
The group's paper describing this new diode, “Near unity ideality factor and Shockley-Read-Hall lifetime in GaN-on-GaN p-n diodes with avalanche breakdown” is published in the American Institute of Physics Applied Physics Letters.