Preconditioning of Ohmic p-GaN power HEMT for reproducible Vth measurements

The fluctuation of the threshold voltage (V_th) presents a challenge while monitoring electrical drift in reliability studies of GaN HEMTs. While technologies, such as ohmic p-GaN, may lessen V_th fluctuations, the issue of recoverable charge trapping still remains. Therefore, it is crucial to adopt novel characterization methods when conducting reliability studies, in order to measure intrinsic changes rather than the charge-trapping effects that exist even in non-degraded transistors. One method expounded in this paper allows for a reliable and replicable measurement of V_th for an ohmic p-GaN gate HEMT GaN. A dedicated gate-bias profile is introduced immediately prior to the threshold-voltage measurement to stabilize it. This preconditioning phase necessitates a negative bias voltage followed by a suitably high voltage to be effective. The novel protocol introduced is also shown to be applicable to other HEMT GaN structures.