Silicon Carbide (SiC) Ultraviolet (UV) phototransistors with bidirectional bias response were fabricated and analyzed in this letter. The results showed that the fabricated UV phototransistor exhibited stable photoelectric response characteristics and transistor characteristics under both forward and reverse voltages, owing to the structure design of the epi-layers, while the mechanism of the bidirectional response was also studied. The difference in photocurrent under different bias voltages and wavelengths of UV illumination were mainly due to the variation of the absorption coefficient with wavelength and the change in the width of the space charge regions, which ultimately led to a difference in the number of photo-generated carriers. The time response characteristics of the detector showed that there were time delays when the detector was turned on and turned off, which was caused by the photo minority carriers in the depletion layer of the base-collector junction.

Silicon carbide (SiC) ultraviolet (UV) phototransistors with normal operation up to 550 °C were fabricated and analyzed in this article. Under 280 nm UV illumination, the responsivity has reached 0.016 and 0.13 A/W at room temperature (RT) and 400 °C, respectively. In addition, the responsivity showed a trend of increasing and then decreasing with rising temperature, and reaching a peak at 400 °C. This phenomenon suggested that there might be an optimal detection temperature for SiC UV phototransistor detectors (PTDs), and this temperature could be tuned by changing the physical parameters of the device. Moreover, this property could be exploited in reverse for the estimation of the temperature range. The transient response characteristics of the detector showed that there was a hysteresis at shutdown, which was caused by the increase of the electron and hole density with temperature to increase the capacitance of the p-n junction depletion layer, resulting in deterioration of frequency characteristics. This work is significant for developing high-temperature 4H-SiC-based UV PDs.

Micro-pixels based on 3-D 4H-silicon carbide (4H-SiC) NPN phototransistors for optoelectronic integration are designed and analyzed in this article for the first time. Pixels with linear, hexagonal, and octagonal layouts demonstrate different results in optical responsivity, delay, spectral response, and high-temperature characteristic. The device operates at a low biased voltage of 5 V. Under 270-nm ultraviolet (UV) illumination, the responsivity of the hexagonal structure reaches 254 A/W at 300 K, and the spectral response shows a great potential of deep UV detection of wide-range wavelength. Furthermore, the transient delay is reduced by large junction area ratio due to the new structure design. The lowest delay performed by the octagonal structure is 55 $\mu$ s, which reveal the potential of high-frequency application. Under high-temperature conditions, the responsivity of the device is significantly improved. The responsivity of hexagonal type can reach 1050 A/W at a light intensity of 100 $\mu$ W/cm $^{\text{2}}$ , which is suitable for detecting weak UV light in elevated temperature environments up to 800 K. Overall, micro-pixel with octagonal structure holds great potential for applications in high-resolution UV imaging in high-temperature environments.

Silicon carbide (SiC) ultraviolet (UV) phototransistor detectors (PTDs) with platinum (Pt) nanoparticles (NPs) were fabricated and analyzed in this article. We realized a controllable variation of the average diameter of Pt NPs in 40–100-nm range by changing the experimental conditions. Under 280-nm UV illumination, the responsivity of the PTD with 50-nm Pt NPs has reached 0.257 A/W and the quantum efficiency has reached 113.8%, which is 2.47 times higher than the PTD without Pt NPs. In contrast, the PTD with 100-nm Pt NPs has a responsivity of 0.174 A/W and a quantum efficiency of 77.1%, which is 1.67 times higher than the PTD without Pt NPs. For the switching characteristics, due to the electric field enhancement effect of the localized surface plasmon resonance (LSPR), the turn-on time of the PTDs with Pt NPs is shortened by 7%–14% compared to the PTD without Pt NPs. In addition, it is found that PTDs with larger sized NPs have larger probing currents at a deep-UV wavelength, a phenomenon that can be explained by advanced resonances induced by the changes in NP size. This result can also provide ideas for SiC probing at short-wave UV region (UVC).