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Achieving high-performance fully-vertical GaN devices on low-cost and large-scale foreign substrates are highly attractive for the development of device technology. In this work, by performing pulsed laser lift-off and laser annealing techniques, high-performance fully-vertical GaN Schottky barrier diodes (SBDs) with superior N-face ohmic contact characteristics are demonstrated. The resulting device exhibits low specific contact resistivity of $3.51\times 10^{-{5}}\,\,\Omega \cdot $ cm2 and differential specific on-resistance of 0.58 $\text{m}\Omega \cdot $ cm2, as well as intact anode Schottky contact. In particular, this device demonstrates robust electrothermal robustness, such as the largest surge current density of 15.6 kA/cm2 to date. Moreover, by implementing N-implanted termination, the breakdown voltage of the device is remarkably enhanced from 240 to 523 V, which is competitive with the state-of-the-art quasi-vertical SBDs. These results reveal the notable potential of pulsed laser lift-off/annealing combined with N-implanted termination for realizing fully-vertical devices.

This work demonstrates the robust single-event irradiation hardness in 650-V E-mode p-GaN HEMTs with source-connected buried metal structure. Such device design notably contributes to the removal of irradiation-induced holes accumulated in the reverse-biased p-GaN/ AlGaN/GaN (p-i-n) junction region, thereby improving irradiation robustness against single-event burnout (SEB). The resulting device exhibits significantly improved SEB voltages of 558 and 467 V under heavy ion linear energy transfer ( $LET_{\text {ion}}$ ) conditions of 75.7 and 86.3 MeV $\cdot $ cm2/mg, respectively, setting a new performance record for GaN-based power devices. Moreover, based on pulsed laser equivalent heavy ion irradiation system configured with a power switching circuit, a high power conversion efficiency of 95% is demonstrated under 77.6 LET PL, 300 W/500 kHz conditions. This work thus makes a significant step toward reaching the promise of GaN devices for radiation applications.

In this work, a 4H-SiC EUV photodiode (PD) with lateral p-n junction formed by selective-area ion implantation is investigated, in which grid-shaped p-type contact region is designed for enhancing effective EUV light absorption. The large area SiC PD with 9 mm diameter exhibits a low dark current density of $\sim 9$ pA/cm2 and a high responsivity of 0.07 A/W at 13.5 nm under 5 V reverse bias. The detectivity of PD is further determined to be $\sim {5}.{9}\times {10} ^{{12}}$ cmHz $^{{0}.{5}}\text{W}^{-{1}}$ based on 1/f noise test. Two-dimensional photocurrent mapping of photosensitive area indicates that the non-uniformity of photo-responsivity at 13.5 nm is less than 0.67%. When tested by using a 266 nm pulse laser, the PD shows a fast rise time of ~4.3 ns in transient response measurement. The PD also exhibits low dark current, stable capacitance and responsivity at elevated temperatures up to 150 °C, suggesting that the detector has good potential for high-temperature operation.

In this work, based on a series of readout-electronic strategy explorations for the Geiger mode 4H-SiC avalanche photodiodes (APDs), simultaneous low after-pulse rate and preserved single-photon detection efficiency (SPDE) have been achieved, facilitating a comprehensive analysis on the physics origin of the dark counts. The characterizations with a passive quenching circuit indicate an evidently larger dark count rate (DCR) in the SiC APDs based on the ion implantation process. By utilizing a double-gate readout strategy, the after-pulse probability distribution in the time domain has been characterized, featuring a quick drop with time. Meanwhile, gated external bias could effectively reduce the DCR from 35% to 5%, but would sacrifice the SPDE. By developing active quenching circuit with fast quenching and reset components, after-pulse impact has been mostly alleviated with maintained SPDE. This work has then realized the analysis on the DCR characteristics in 4H-SiC APD with well suppressed after pulses, and clarified the point-defect dominated tunneling carrier generation in the dark count, as well as the prior avalanche event dominated after pulse probability distributions in time domain.

SiC phototransistor has been widely studied for the weak UV detection, however, is facing with severe limit for the detection of UV light below $\mu \text{W}$ /cm2. In this work, reach-through-collector configuration based SiC phototransistor has been demonstrated, where sensitivity of base region to the bias voltage has been largely alleviated, achieving fine control on the neutral zone in the base layer. The tunable gain range for the weak UV light has been extended to over $10^{{8}}$ , while the dark current is kept below 0.5 pA, and the noise figure is as low as $10^{-{28}}\,\,\text{A}^{{2}}$ /Hz at 10 Hz. These characteristics contribute to a UV-to-visible rejection ratio of ${1}.{9}\times {10} ^{{7}}$ and a detectivity of ${4}.{9}\times {10} ^{{15}}$ cm $\cdot $ Hz $^{\text {1/{2}}}$ /W, enabling a UV detection with power as low as 5 nW/cm2. With additional advantageous dynamic response performance, this reach-through collector based PTD solution paves a way to SiC based ultra-weak UV detection technology.

This work presents the demonstration of a GaN based low-energy X-ray single photon detector with photon energy resolution capability. By adopting the GaN-on-GaN high quality epitaxy technique, slant mesa termination structure, and well-modified ohmic contact layer, a fully vertical GaN p-i-n diode with leakage in pA level and low parasitic resistance has been fabricated, achieving a low-energy X-ray photon detector with extremely low noise figure below $1\times 10^{-{28}}\,\,\text{A}^{2}$ /Hz and fast response within $1.0~\mu \text{s}$ . With a specifically established reset charge sensitive amplification circuit, superior linearity has been obtained between the output Gaussian peak position and the photon energy in the investigated range of approximately 10 keV to 20 keV, enabling the photon energy resolution with a high carrier collection ratio. This work thus validates the merits of GaN in low-energy X-ray detection, providing a promising solution with high temperature stability and radiation hardness.

In this work, a pulsed ultraviolet (UV) laser positioning system based on 4H-SiC four-quadrant photodetectors (4-QDs) is demonstrated and applied to the self-calibration of laser deflection angle. The 4H-SiC 4-QD with a photosensitive area of 8 mm in diameter exhibits high uniformity in performance across all quadrants, including a low dark current of ~7 pA and a peak responsivity of 0.12 A/W at 275 nm. Charge-sensitive amplifiers (CSAs) are developed for the linear amplification of the photocurrents. Based on a 266 nm pulsed laser, a 4-QD, CSAs and a displacement platform, the system exhibits excellent positioning performance over an area of $600\times 600\mu $ m, with a mean absolute error of $5.52\mu $ m. Finally, a prototype laser beam deflection angle self-calibration system based on the fabricated 4-QD is realized, achieving a calibration error below 0.0015° with a relative error below 0.5%.

Highly stable threshold voltage $({V}_{\text {TH}})$ characteristics are an essential reliability requirement for p -GaN/AlGaN/GaN high-electron-mobility transistors (p-GaN HEMTs) to withstand various gate bias stresses for power applications. In this work, we demonstrate high- ${V}_{\text {TH}}$ (3.0 V) p-GaN HEMTs with robust ${V}_{\text {TH}}$ stability by p -GaN gate engineering via Mg doping and activation. The ${V}_{\text {TH}}$ degradation rates of the resulting device under both pulsed- ${I}/{V}$ and bias temperature instability (BTI) stress conditions are less than 10% at high temperatures up to 150°, which is much lower than that of conventional Schottky-type p -GaN HEMTs (20%–30%). Such notable ${V}_{\text {TH}}$ characteristics are due to the impact ionization (I.I.)-dependent hole compensation under certain gate stress, which effectively alleviates the electron trapping effect and reduces positive ${V}_{\text {TH}}$ shift. The I.I. occurring in the fully depleted p -GaN layer has been confirmed by both positive temperature-dependent gate breakdown characteristics and numerical simulations. Furthermore, shallow- and deep-level hole traps are identified in the gate-stack of high- ${V}_{\text {TH}}$ devices by performing the deep-level transient spectroscopy (DLTS) technique. Consequently, the trapping effect associated with hole traps may also alleviate the undesired electron-trapping-induced ${V}_{\text {TH}}$ shift. These results provide a critical understanding of the ${V}_{\text {TH}}$ stability of the high- ${V}_{\text {TH}}$ p -GaN HEMTs (HVT-HEMTs) and important design guidance for commercial device development.