The COVID-19 pandemic has highlighted the need for rapid and sensitive detection of SARS-CoV-2. Here, we report an ultrasensitive SARS-CoV-2 immunosensor by integration of an AlGaN/GaN high-electron-mobility transistor (HEMT) and anti-SARS-CoV-2 spike protein antibody. The AlGaN/GaN HEMT immunosensor has demonstrated the capability to detect SARS-CoV-2 spike proteins at an impressively low concentration of 10−22 M. The sensor was also applied to pseudoviruses and SARS-CoV-2 ΔN virions that display the Spike proteins with a single virion particle sensitivity. These features validate the potential of AlGaN/GaN HEMT biosensors for point of care tests targeting SARS-CoV-2. This research not only provides the first HEMT biosensing platform for ultrasensitive and label-free detection of SARS-CoV-2.@en

The authors regret an error in the abstract of the published article: the text ‘‘(i) the Schottky emission mechanism at a low reverse voltage (0–1 V) before the current is fully turned on.’’ should be changed to ‘‘(i) the Schottky emission mechanism at a low reverse voltage (0 to 1 V) before the current is fully turned on.’’ This change does not affect the main conclusions of the manuscript. The authors would like to apologize for any inconvenience caused. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.

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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.

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Based on our proposed precision two-step gate recess technique, a suspended gate-recessed Pt/AlGaN/GaN heterostructure gas sensor integrated with a micro-heater is fabricated and characterized. The controllable two-step gate recess etching method, which includes O2 plasma oxidation of nitride and wet etching, improves gas sensing performance. The sensitivity and current change of the AlGaN/GaN heterostructure to 1-200 ppm NO2/air are increased up to about 20 and 12 times compared to conventional gate device, respectively. The response time is also reduced to only about 25 % of value for conventional device. The sensor has a suspended circular membrane structure and an integrated micro-hotplate for adjusting the optimum working temperature. The sensitivity (response time) increases from 0.75 % (1250 s) to 3.5 % (75 s) toward 40 ppm NO2/air when temperature increase from 60°C to 300°C. The repeatability and cross-sensitivity of the sensor are also demonstrated. These results support the practicability of a high accuracy and fast response gas sensor based on the suspended gate recessed AlGaN/GaN heterostructure with an integrated micro-heater.

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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. The WO₃nanolayer was deposited by physical vapor deposition (PVD) for deep UV absorption and the micro-heater was integrated for chip level heating and cooling. Our device when exposed to UV wavelength exhibits a high responsivity of 1.67 × 10⁴A W⁻¹at 240 nm and a sharp cut-off wavelength of 275 nm. More importantly, the persistent photoconductivity (PPC) effect can be eliminated by a novel method, mono-pulse heating reset (MHR), which consists in applying an appropriate pulse voltage to the micro-heater right after the removal of the UV illumination. The recovery time was reduced from hours to just seconds without reducing the high responsivity and stability of the photodetector. The UV detection, high responsivity, high stability, controllable recovery process and low production cost of GaN-based photodetectors make these devices extremely attractive for several applications, such as fire detection and missile and rocket warning.

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A suspended WO₃-gate AlGaN/GaN heterostructure photodetector integrated with a micro-heater is micro-fabricated and characterized for ultraviolet photo detection. The transient optical characteristics of the photodetector at different temperatures are studied. The 2DEG-based photodetector shows a recovery (170 s) time under 240 nm illumination at 150 ℃. The measured spectral response of WO₃-gate AlGaN/GaN heterostructure shows a high response in deep ultraviolet range. Responsivity at 240 nm wavelength is 4600 A/W at 0.5 V bias. These characteristics support the feasibility of a high accuracy deep UV detector based on the suspended AlGaN/GaN heterostructure integrated with a micro-heater.

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This paper demonstrates a method to reduce the decay time in AlGaN/GaN photodetectors by a pulsed heating mode. A suspended AlGaN/GaN heterostructure photodetector integrated with a micro-heater is fabricated and characterized under ultraviolet illumination. We have observed that the course of persistent photoconductivity was effectively accelerated by applying pulsed heating. The decay time is significantly reduced from 175 s by DC heating to 116 s by 50 Hz pulsed heating at the same power (280 mW). With the same pulse duty cycle and a 50 Hz pulsed heating frequency, a reduction of 30%-45% in decay time is measured compared to DC heating.

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