In this work, we investigated the temperature-dependent photodetection behavior of a high-performance AlGaN/GaN-based ultraviolet phototransistor (UVPT) operating under 265 nm illumination. As the temperature continuously rises from room temperature to 250 °C, the photocurrent of a device increases in the beginning but suffers from degradation afterwards. This can be explained by the competing process between the generation and recombination rate of photo-induced carriers in the UVPT at room and high temperatures. Intriguingly, we found that the optimal operating temperature for our UVPT is around 50 °C, featuring a high peak responsivity of 1.52 × 105 A/W under a light intensity of 45  μW/cm2. Furthermore, the photoresponse time of our UVPT is also highly temperature-dependent, exhibiting the shortest rise time of 50 ms at 100 °C while the decay time is monotonically reduced as the temperature rises to 250 °C. Notably, our AlGaN/GaN-based UVPTs exhibit ultra-high responsivity at high temperatures, which have outperformed those earlier reported UV photodetectors in the form of different device architectures, highlighting the great potential of such device configurations for harsh environment applications.

In this Letter, we perform a comprehensive investigation on the optical characterization of micro-sized deep-ultraviolet (DUV) LEDs (micro-LEDs) emitting below 280 nm, highlighting the light extraction behavior in relation to the design of chip sidewall angle. We found that the micro-LEDs with a smaller inclined chip sidewall angle ( ∼ 33 ∘ ) have improved external quantum efficiency (EQE) performance 19% more than that of the micro-LEDs with a larger angle ( ∼ 75 ∘ ). Most importantly, the EQE improvement by adopting an inclined sidewall can be more outstanding as the diameter of the LED chip reduces from 40 to 20  μ m . The enhanced EQE of the micro-LEDs with smaller inclined chip sidewall angles can be attributed to the stronger reflection of the inclined sidewall, leading to enhanced light extraction efficiency (LEE). In the end, the numerical optical modeling further reveals and verifies the impact of the sidewall angles on the LEE of the micro-LEDs, corroborating our experiment results. This Letter provides a fundamental understanding of the light extraction behavior with optimized chip geometry to design and fabricate highly efficient micro-LEDs in a DUV spectrum of the future.

In this work, an E-mode AlGaN/GaN-based HEMTs with a graded AlGaN cap layer (GACL) is proposed and numerically studied by Silvaco TCAD. The GACL is designed with a decreasingly graded Al composition x along [0001] direction and the initial x is smaller than the Al composition of the Al0.2Ga0.8N barrier layer (BL). This GACL scheme can simultaneously produce high-concentration polarization-induced holes and negative net polarization charges at the GACL/BL interface. This can facilitate the separation of the conduction band and Fermi level at the 2DEG channel and therefore benefit the normally-OFF operation of the device. The optimized graded-AlGaN-gated (GAG) metal-semiconductor (MES) HEMT can achieve a large threshold voltage of 4 V. Furthermore, we demonstrated that shortening the gate length on the GACL and inserting an oxide layer between the gate and GACL can be both effective to suppress gate leakage current, enhance gate voltage swing, and improve on-state drain current of the device. These numerical investigations can provide insights into the physical mechanisms and structure innovations of the E-mode GaN-based HEMTs of the future.

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