This paper provides a comprehensive review of recent progress in GaN-based gas sensors with a focus on their dynamic-related responses, mechanisms and applications, which are important for sensing performance, efficiency, and signal processing.

We present a novel p-gallium nitride (GaN) gate HEMT structure with reduced hole concentration near the Schottky interface by doping engineering in metal-organic chemical vapor deposition (MOCVD), which aims at lowering the electric field across the gate. By employing the additional unintentionally doped GaN (u-GaN) layer, the gate leakage current is suppressed and the gate breakdown voltage is boosted from 10.6 to 14.6 V with negligible influence on the threshold voltage and ON-resistance. A reduced Mg concentration in the u-GaN layer was confirmed by secondary-ion mass spectrometry. Time-dependent gate breakdown measurements reveal that the maximum gate drive voltage increases from 6.2 to 10.6 V for a ten-year lifetime with a 1% gate failure rate, which effectively expands the operating voltage margin of the p-GaN gate HEMTs without any other additional process step.

A robust ohmic contact process with ultralow contact resistivity on p-GaN/AlGaN/GaN is demonstrated. An in-situ removal of GaO _X interfacial layer after contact metal deposition is developed. Using the novel Mg/Pt/Au stack as the contact metal, a stable ohmic contact is obtained after 450°C/300 s annealing with ohmic contact resistivity of $12 \Omega \cdot {\mathrm {mm}}$ ( $1.8\times 10^{-5}\, \Omega \cdot {\mathrm {cm}}^{2}$ ). A new ohmic contact formation mechanism on p-GaN/AlGaN/GaN is also proposed.

In this paper, DC, transient, and RF performances among AlGaN/GaN HEMTs with a no field plate structure (basic), a conventional gate field plate structure (GFP), and a double floating field plate structure (2FFP) were studied by utilizing SILVACO ATLAS 2D device technology computer-aided design (TCAD). The peak electric fields under the gate in drain-side can be alleviated effectively in 2FFP devices, compared with basic and GFP devices, which promotes the breakdown voltage (BV) and suppresses the current collapse phenomenon. As a result, the ON-resistance increase caused by the current collapse phenomena is dramatically suppressed in 2FFP ~19.9% compared with GFP ~49.8% when a 1 ms duration pre-stress was applied with V_ds = 300 V in the OFF-state. Because of the discontinuous FP structure, more electric field peaks appear at the edge of the FFP stacks, which leads to a higher BV of ~454.4 V compared to the GFP ~394.3 V and the basic devices ~57.6 V. Moreover, the 2FFP structure performs lower a parasitic capacitance of C_gs = 1.03 pF and C_gd = 0.13 pF than those of the GFP structure (i.e., C_gs = 1.89 pF and C_gd = 0.18 pF). Lower parasitic capacitances lead to a much higher cut-off frequency (f_t) of 46 GHz and a maximum oscillation frequency (f_max) of 130 GHz than those of the GFP structure (i.e., f_t = 27 GHz and f_max = 93 GHz). These results illustrate the superiority of the 2FFP structure for RF GaN HEMT and open up enormous opportunities for integrated RF GaN devices.

This work adopts interface charge engineering to fabricate normally off metal–insulator–semiconductor high electron mobility transistors (MIS-HEMTs) on an in situ SiNx/AlGaN/GaN platform using an in situ O3 treatment performed in the atomic layer deposition system. The combination of in situ SiNx passivation and an O3-treated Al2O3/AlGaN gate interface allows the device to provide an excellent breakdown voltage of 1498 V at a low specific on-resistance of 2.02 mΩ cm2. The threshold voltage is increased by 2 V by significantly compensating the net polarization charges by more than five times with O3 treatment as well as reducing the interface traps and improving the high-temperature gate stability. Furthermore, a physical model of fixed charges at the Al2O3/AlGaN interface is established based on dielectric thickness-dependent linear fitting and numerical calculations. The matched device performance and simulated energy band bending elucidate the O3-treated fixed-charge modulation mechanism, providing a practical method for producing normally off GaN MIS-HEMTs.