High Voltage AlGaN/GaN Heterojunction Transistors

The use of AlGaN/GaN HEMTs and HBTs for switching power supplies is explored. With its high electron velocities and breakdown fields, GaN has great potential for power switching. The field-plate HEMT increased breakdown voltages by 20% to 570V by reducing the peak field at the drain-side edge of the gate. The use of a gate insulator is also investigated, using both JVD SiO₂ and e-beam evaporated SiO₂ to reduce gate leakage, increasing breakdown voltages to 1050V and 1300V respectively. The power device figure of merit (FOM) for these devices:, is the highest reported for switching devices. To reduce trapping effects, reactively sputtered SIN, is used as a passivant, resulting in a switching time of less than 30 ns for devices blocking over 110V with a drain current of 1.4A under resistive load conditions. Dynamic load results are also presented.

The development of HBTs for switching applications included the development of an etched emitter HBT with a selectively regrown extrinsic base. This was later improved upon with the selectively regrown emitter devices with current gains as high as 15. To improve breakdown in these devices, thick GaN layers were grown, reducing threading dislocation densities in the active layers. A further improvement included the use of a bevelled shallow etch and a lateral collector design to maximize device breakdown.