A low- Magnesium (Mg) out-diffusion normally off p-GaN gated AlGaN/GaN high-electron-mobility transistor (HEMT) was developed using a low-temperature laser activation technique. Conventionally, during the actual p-GaN layer activation procedure, Mg out-diffuses into the AlGaN barrier and GaN channel at high temperatures. In addition, the Al of the AlGaN barrier layer is injected into GaN to generate alloy scattering and to suppress current density. In this study, the GaN doped Mg layer (Mg:GaN)was activated using short-wavelength Nd:YAG pulse laser annealing, and a conventional thermal activation device was processed for comparison. The results demonstrated that the laser activation technique in p-GaN HEMT suppressed the Mg out-diffusion-induced leakage current and trapping effect and enhanced the current density and breakdown voltage. Therefore, using this novel technique, a high and active Mg concentration and a favorable doping confinement can be obtained in the p-GaN layer to realize a stable enhancement-mode operation.

In this study, a 50-nm Al_0.05Ga_0.95N back barrier (BB) layer was used in an AlGaN/GaN high-electron-mobility transistor between the two-dimensional electron gas channel and Fe-doped/C-doped buffer layers. This BB layer can reduce the channel layer. The BB layer is affected by doped carriers in the buffer layer and the conduction energy band between the channel and the buffer layers. The I_on/I_off ratio of the BB device was 3.43 × 10⁵ and the ratio for the device without BB was 1.91 × 10³. Lower leakage currents were obtained in the BB device because of the higher conduction energy band. The 0.25-μm gate length device with the BB exhibited a high current gain cutoff frequency of 26.9 GHz and power gain cutoff frequency of 54.7 GHz.

Metal–insulator–semiconductor p-type GaN high-electron-mobility transistor with an Al₂O₃/AlN deposited by atomic layer deposition was investigated. The selected insulator, AlN has been proven to have a good interface with GaN. A traditional p-GaN device without an Al₂O₃/AlN layer was processed for comparison. Due to the Al₂O₃/AlN layer, the gate leakage was lower, and the threshold voltage was higher, at 4.7 V. Additionally, excellent turn-on voltage was obtained. Furthermore, low current degradation and smaller V_TH shift at high temperatures was also observed. Hence, growing a good-quality Al₂O₃/AlN layer can achieve an enhancement-mode operation with superior stability and high gate swing region.

In this study, AlGaN back barriers (B.B.) with different Al mole fractions and thicknesses were used in AlGaN/GaN high electron mobility transistors (HEMTs) to improve device performance. Relative to thickness, a proper Al mole fraction (Al_0.08GaN) of the B.B. more strongly affected the device’ I_on/I_off ratio. It exhibited a low leakage current and high I_on/I_off ratio of approximately 10⁶. Relative to B.B. mole fraction, B.B. thickness more greatly affected the devices’ horizontal breakdown voltage (760V) and LFN characteristics. Increasing the Al mole fraction and the thickness of the B.B. more strongly affected the dynamic R_ON. The current gain cut-off frequency (f_T) and maximum stable gain cut-off frequency (f_max) were 5.2 GHz and 10.5 GHz, respectively, for the Al_0.08GaN B.B. device.