In this work, we demonstrate a high-performance ultraviolet phototransistor (UVPT) based on the AlGaN/GaN high-electron mobility transistor (HEMT) configuration. When the device is biased at off state, the peak photoresponsivity (R) of 3.6 × 107 A/W under 265 nm illumination and 1.0 × 106 A/W under 365 nm illumination can be obtained. Those two R values are one of the highest among the reported UVPTs at the same detection wavelength under off-state conditions. In addition, we investigate the gate-bias (VGS) dependent photoresponse of the fabricated device with the assistance of band structure analysis. It was found that a more negative VGS can significantly reduce the rise/decay time for 265 nm detection, especially under weak illumination. This can be attributed to a largely enhanced electric field in the absorptive AlGaN barrier that pushes the photo-generated carriers rapidly into the GaN channel. In contrast, the VGS has little impact on the switching time for 365 nm photodetection, since the GaN channel has a larger absorption depth and the entire UVPT simply acts as a photoconductive-type device. In short, the proposed AlGaN/GaN HEMT structure with the superior photodetection performance paves the way for the development of next generation UVPTs.

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 work, the device characteristics of GaN-based high-electron-mobility transistors (HEMTs) were systematically investigated by the direct current (DC) and low-frequency noise (LFN) measurements within the temperature ranging from 300 K to 4.2 K. The temperature-dependent behavior of the on- and off-state electrical properties was statistically analyzed, highlighting an overall improved device performance under the cryogenic temperatures. In addition, the LFN of the device exhibited an evident behavior of 1/f noise from 10 Hz to 10 kHz in the measured temperature range and can be well described by the carrier number fluctuations with correlated mobility fluctuations (CNF/CMF) model down to 4.2 K. Based on this model, we further extracted and discussed the defect-related behavior in the devices under low-temperature environments. These experimental results provide insights into the device characteristics of GaN-based HEMTs under cryogenic environments, motivating further studies into the GaN-based cryo-devices and systems.

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In this work, the electrical characteristics of AlGaN/GaN high-electron-mobility transistors (HEMTs) on vicinal c-plane sapphire substrates with different misoriented angles are investigated. As the angle increases from 0.2°, 1.0° to 4.0°, an enlarged width and height of surface step bunching as well as significantly enhanced electron mobility from 957, 1123 to 1246 cm2/V s were measured. As a result, a large boost in the maximum output current (IDmax) from ∼300 mA/mm (on a 0.2° substrate) to ∼650 mA/mm (on a 4.0° substrate) can be observed. Importantly, HEMTs on 1.0° and 4.0° substrates exhibit an obvious anisotropic electrical behavior: the IDmax along the [11-20] orientation is larger than that along the [10-10] orientation. Such a difference becomes more distinct as the misoriented angle increases, attributing to the lifted step height that would introduce a potential barrier for the electron transport along the [10-10] orientation. In short, this work demonstrates an effective approach toward the realization of high-performance HEMTs with anisotropic electrical behavior on a single device platform.