Normally-off HEMTs have been fabricated with regrown p-GaN gate and SiN _x passivation by Low-pressure chemical vapor deposition (LPCVD) using an AlN pre-layer, featuring a high-temperature passivation-first technique with no incompatibility issues. Through careful surface treatments, high-quality interfaces (regrown p-GaN/AlGaN and SiN _x /AlGaN), as well as a stable p-GaN contact, can be achieved, enabling a robust gate operation and improved dynamic performance. The as-fabricated device exhibits a low reverse gate leakage of 2 nA/mm @ V _GD = −200 V, a stable forward gate current of $10~\mu \text{A}$ /mm @ V _GS = 5 V, a positive threshold voltage of +1.7 V @ ${I}_{\text {DS}} = {10}\,\,\mu \text{A}$ /mm with a high saturation current of 435 mA/mm, a high I _on /I _off ratio of ${5}\times {10}^{10}$ , and a low R _on,d /R _on,s ratio of 1.5. The as-developed technique with the LPCVD SiN _x passivation and p-GaN gate regrowth may provide a way to enhance the performance of p-GaN E-HEMTs.

This Letter studies the reverse leakage and breakdown mechanisms of vertical GaN-on-Si Schottky barrier diodes (SBDs) with and without argon-implanted termination (ArIT). The electrical leakage characteristics in the vertical GaN-on-Si SBD without edge termination sequentially go through the thermionic field emission, variable range hopping (VRH), and trap-assisted tunneling conduction mechanisms as the reverse bias increases gradually. Its leakage and breakdown mechanisms are limited by the edge electric field crowding effect. While for the vertical GaN-on-Si SBD with ArIT (ArIT-SBD), the electrons conduction at a low reverse bias, following the space-charge-limited conduction (SCLC) model, is limited by the damage-induced traps in the implanted GaN. As the reverse bias increases up to the occurrence of breakdown, the VRH and SCLC dominate the leakage mechanism of the ArIT-SBD, which stem from intrinsic traps in GaN grown on Si. A rapidly growing leakage under a low reverse bias and enhanced breakdown voltage performance in the ArIT-SBD is attributed to the charging of the damage-induced traps in implanted GaN. This Letter not only gives in-depth insights of vertical GaN-on-Si SBDs but also provides a useful design guidance of implanted termination for high-voltage power devices.

A high-performance quasi-vertical GaN Schottky barrier diode (SBD) was successfully fabricated by using a high-quality n ^- -GaN drift layer with a precisely-controlled n-type doping. A high current on/off ratio of 10 ¹⁰ , an ideality factor of 1.03, a low specific on-resistance of 1.41 mΩ·cm ² , and a relatively high breakdown voltage (BV) of 250 V have been achieved for the SBD without edge termination. Furthermore, with an Argon-implanted termination, the as-fabricated GaN-on-Si SBD shows a record high BV of 405 V, yielding a critical electric field of ~ 2 MV/cm, while the forward conduction characteristics are well maintained.

This work demonstrates a novel Nitrogen-implanted (N-implanted) guard ring (GR) technology for the 600-V quasi-vertical GaN-on-Si Schottky barrier diode (SBD). The GR parameters are designed and studied in detail by the TCAD simulation. With a 4.4- $\mu \text{m}$ -thick GaN drift layer, seven GRs with a precise design greatly enhance the breakdown voltage of GaN SBDs from ~290 to ~600 V, and barely degrade the ON-state characteristics, including a high ${I}_{ {\scriptscriptstyle { \mathrm {ON}}}}/{I}_{ {\scriptscriptstyle { \mathrm {OFF}}}}$ of 10 ¹¹ , a low ideality factor of 1.06, a low turn-on voltage of 0.64 V (at 1 A/cm ² ), and a low-specific ON-resistance ( ${R}_{ {\scriptscriptstyle { \mathrm {ON}}},{\mathrm {sp}}}$ ) of 1.40 $\text{m}\Omega ~\cdot ~{\mathrm {cm}}^{2}$ , leading to a record Baliga’s figure of merit (BFOM) of 0.26 GW/cm ² among all the reported vertical GaN-on-Si SBDs. At 175 °C, the SBD with seven GRs shows a slightly increased ${R}_{ {\scriptscriptstyle { \mathrm {ON}}},{\mathrm {sp}}}$ of 1.86 $\text{m}\Omega ~\cdot ~{\mathrm {cm}}^{2}$ and an excellent electrical characteristic even under a reverse bias of 380 V, implying a high-temperature operation capability of N-implanted GRs.

Gate reliability and its degradation mechanism were studied for the normally-off high electron mobility transistors (HEMTs) with regrown p-GaN gate and AlN/SiNx stack passivation. Through comparing the forward leakage current in two designed structures, the conduction mechanism is determined to be Fowler-Nordheim tunneling whose current is independent with temperature when the Pd/p-GaN Schottky junction is under high electric field. Even for the regrown p-GaN gates, this Schottky junction fails at first, resulting in an abruptly increase of gate current. The maximum gate operation voltage with a failure rate of 1% for 10-year lifetime is estimated to be about 6.87 V and 6.07 V at room temperature by adopting power law and exponential law as extrapolation fitting, respectively. Degradation process monitoring reveals that the net acceptor concentration NA extracted through C-V fitting presents an apparent decreasing trend from 3.8 × 1019 to 1.1 × 1019 cm-3 with stress time increased from 30 to 2600 sec. This is assumed to be related with the defects generation in the Schottky depletion region under high tunneling current and high electric field. These analyses show the feasibility of the normally-off HEMTs with a regrown p-GaN gate and AlN/SiNx stack passivation for practical applications, giving directions for further improving the gate breakdown voltage and lifetime.