Study on Effects of GaN Trap Depth Profiles to Transient Response in GaN HEMTs on GaN Substrates by Device Simulation

Effects of GaN trap depth profile to transient response for GaN HEMTs on GaN substrates were investigated by device simulation. The device structures for the simulation have semi-insulating 400-μm-thick GaN substrate with trap density of 5.0 × 10
¹⁷
cm
^-3
and energy level of 0.5 eV. The transient responses were calculated as the drain current depending on time by changing bias from off-state to on-state condition. The derivative of drain current respect to time has a peak at 8 msec corresponded to the characteristics time of the trap. The traps under the gate edge of the drain side in deep GaN channel region were found to affect the transient response. In the case of the structure with additional trap layer in the channel region, the additional trap dominated the transient response at the trap density as large as 5.0 × 10
¹⁷
cm
^-3
. When the buffer layer removed, the thickness reduction of the channel layer resulted to the degradation of the transient response.