A high responsivity and controllable recovery ultraviolet (UV) photodetector based on a tungsten oxide (WO₃) gate AlGaN/GaN heterostructure with an integrated micro-heater is reported for the first time.

Recent research focusing on wide-bandgap and two-dimensional materials with a Schottky junction has provided a new concept for ultraviolet photodetectors. However, the working mechanism of the Schottky junction-based detector varies depending on the photosensitive materials used and the device structure. We demonstrated a TiO₂/AlGaN/GaN heterostructure-based photodetector with a Schottky junction, integrating an ultraviolet photosensitive TiO₂ nanolayer, a two-dimensional electron gas (2DEG) field effect transistor, and a metal–semiconductor Schottky diode. The spectral response wavelength region of the detector is 200–365 nm and the peak responsivity is 37.396 A W⁻¹ at −5 V bias under 240 nm UV illumination, respectively. Meanwhile, a peak photo-to-dark current ratio (PDCR) of 5.1 × 10² at −2 V bias voltage was observed under 274 nm UV irradiation. This Schottky-based 2DEG heterostructure detector can realize three dominant working principles: (i) the Schottky emission mechanism at a low reverse voltage (0–1 V) before the current is fully turned on, (ii) the Poole-Frenkel emission mechanism at a medium reverse voltage (−1 to −2 V) with peak PDCR, and (iii) the Fowler-Nordheim tunneling mechanism at a high reverse voltage (>−2 V) with a high responsivity. Continuous cycle response measurement results indicate that the detectors have good response repeatability and reliability. The characteristics of response wavelength, responsivity, and stability show that the detector can be used for several commercial applications, including sunscreen UV monitoring and LED sterilization light source detection.

A 365-nm UV LED was fabricated based on embedded nanoporous AlGaN distributed Bragg reflectors (DBR) by electrochemical etching. The porous DBR had a reflectance of 93.5% at the central wavelength of 365 nm; this is the highest value of porous AlGaN DBRs below 370 nm which has been reported so far. An innovative two-step etching method with a SiO₂ sidewall protection layer (SPL) was proposed to protect the n-AlGaN layer and active region of UV LED from being etched by the electrolyte. The DBR-LED with SPL showed 54.3% improvement of maximal external quantum efficiency (EQE) and 65.7% enhancement of optical power at 100 mA without any degeneration in electrical properties, compared with the un-etched standard LED sample. This work has paved the way for the application of electrically-pumped UV LEDs and VCSELs based on nanoporous AlGaN DBRs.

A high-sensitivity pH sensor based on an AlGaN/GaN high-electron mobility transistor (HEMT) with a 10 nm thick Au-gated sensing membrane was investigated. The Au nanolayer as a sensing membrane was deposited by electron-beam evaporation and patterned onto the GaN cap layer, which provides more surface-active sites and a more robust adsorption capacity for hydrogen ions (H⁺) and hydroxide ions (OH⁻) and thus the sensitivity of the sensor can be significantly enhanced. A quasi-reference electrode was used to minimize the sensing system for the measurement of the microliter solution. The measurement and analysis results demonstrate that the fabricated sensor exhibits a high potential sensitivity of 58.59 mV/pH, which is very close to the Nernstian limit. The current sensitivity is as high as 372.37 μA/pH in the pH range from 4.0 to 9.18, under a 3.5 V drain-source voltage and a 0 V reference-source voltage. Comparison experiments show that the current sensitivity of the Au-gated sensor can reach 3.9 times that of the SiO₂-gated sensor. Dynamic titration experiments reveal the pH sensor’s ability to promptly respond to immediate pH variations. These findings indicate that this pH sensor can meet most application requirements for advanced medical and chemical analysis.

Optogenetic methods with high temporal and spatial specificity have rapidly become a powerful technique in neuroscience. However, implantable fibers coupled with external laser sources as the traditional stimulated approach, constrain the free movement of experimental animals. In this study, we introduced a wireless-operated miniaturized implantable system with superior biocompatibility. The injectable dual-channel flexible neural probe with blue and orange light-emitting diodes (LEDs) was controlled using a customized circuit module powered by a rechargeable lithium battery. For excitatory and inhibitory neurons, the optical power densities of the blue and orange LEDs transferred to the flexible substrate can reach 25 and 18 mW/mm2, respectively, under an injection current of 5 mA. Moreover, the 2.4 GHz Bluetooth wireless communication protocol integrated into the circuit module enables LEDs to be remotely operated using mobile devices at a distance as far as 22.5 m. The movement traces of behaving animals after stimulation with optical signals can be recorded using an accelerometer and feedback to the terminal through Bluetooth chips. The proposed system provides an effective route for evaluating the functions and analyzing the structures of complicated animals.