Normally-off GaN HEMTs

As silicon transistors have become a staple in everyday usages, other semiconductor materials (specifically III-V materials) are being researched to determine how their differing physical properties can be harnessed toward even better devices or applications. Useful properties of the III-V semiconductor gallium nitride (GaN) compared to silicon are its larger bandgap energy, larger breakdown field, and higher thermal conductivity. These properties allow GaN transistors to more effectively be used as power switching devices with larger current density, switching speeds and better power efficiency than that of Si power devices. The GaN transistor structure used to create these power switching devices is the high electron mobility transistors (HEMT), which has a naturally conducting channel at the hetero-interface between GaN and AlxGa1-xN. Since the source/drain channel is conducting while the HEMT is at equilibrium, the device is considered a normally ON device where it takes no gate voltage for the transistor to have a drain current. This normally ON characteristic of the transistor, however, is a limitation of the device. For safety and OFF mode power saving concerns, it is ideal for the HEMT to be a normally OFF device where the channel is non-conducting with no gate bias. There have been many methods proposed to deplete the channel of its conductive properties and I believe that the pGaN gate method is the most promising. The pGaN gate method entails a gate made of heavily p-type doped GaN. This in turn lowers the equilibrium Fermi level enough to deplete the hetero-interface of a conducting channel. Using Synopsis TCAD simulation software, I created a pGaN gate HEMT structure and explored its normally OFF characteristics and limitations.Ope