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Kink effect is observed in Al0.83In0.17N/GaN high electron mobility transistor by measuring ID-VDS characteristics at a low sweep rate. It is inferred that the kink is induced due to the trapping/detrapping of charge carriers at deep levels present in the GaN buffer in the gate–drain access region. The detrapping of charge carriers from the deep levels is by the hot-electron-assisted mechanism. Two types of traps with activation energies, 0.29 eV (donor-like) and 0.57 eV (acceptor-like) were extracted by temperature-dependent transient drain current analysis. It is concluded that the deep-acceptor-like trap with a large emission time constant is responsible for the kink effect.

In this paper, we report the effect of post-gate metallization annealing on the performance of GaN-based High Electron Mobility Transistors (HEMTs). The performances of HEMTs annealed at 200 °C (HEMT1) and at 400 °C (HEMT2) for 5 minutes in N 2 ambient are compared. While there is a kink in the output characteristics of HEMT1, there is no such kink in the output characteristics of HEMT2. The kink is attributed to impact ionization in the GaN channel. Surface and interface traps of HEMT1 increase the peak electric field at the drain side gate edge and cause impact ionization. The post-gate metallization annealing at a higher temperature reduces the surface and interface traps, which reduces the peak electric field in HEMT2 and suppresses impact ionization. This is substantiated by TCAD simulations. Threshold voltage instability on the application of negative gate bias stress was also examined for these devices. A positive shift in threshold voltage was observed in HEMT1 on the application of negative gate bias stress, whereas the corresponding shift was negative in HEMT2, indicating the presence of two different types of traps in HEMT1 and HEMT2.

An accurate method to extract the thermal resistance (RTH) of GaN-on-Si high electron mobility transistors (HEMTs) is proposed. It is shown that by pulsing the substrate, instead of drain or gate as done in the existing methods, one can significantly reduce the effect of traps on the extraction process. To demonstrate this, HEMTs are fabricated on two wafers, similar in all respects except that one has a carbon-doped buffer and the other does not. We obtain the same value of RTH for the two wafers using the proposed method, while the values are significantly different using the method based on drain pulsing. The extracted RTH is also used in a compact model to demonstrate the accuracy of the proposed method.