A two-terminal 4H-SiC n-p-n bipolar phototransistor detector (PTD) with high gain is demonstrated. It was fabricated using the 4H-SiC epitaxial wafer grown by high-temperature chemical vapor deposition. The PTD shows a large photocurrent and responsivity enhancement over the conventional 4H-SiC p-i-n photodetector (PD). These enhancement effects are owing to the internal gain of the bipolar transistor. The detector shows a high optical gain of ~ 1450 at 360 nm and has a linear response to the ultraviolet (UV) light in the wide light intensity range of 0.7– $700~\boldsymbol \mu \text{W}\boldsymbol /$ cm ² at a low operating voltage of 3 V. The PTD can respond to the UV light from 220 to 340 nm and the peak responsivity is $\sim 125~\text{A}\boldsymbol /\text{W}$ at 275 nm. This work is significant for developing high-performance SiC-based bipolar phototransistors.

In this article, we report the first experimental results of a novel 4H-silicon carbide (SiC) p-i-n photodetector based on a vertical nanocone array (NCA). It is fabricated by electron beam lithography and inductively coupled plasma (ICP) etching technology. The performance of static and dynamic behavior was studied systematically. It shows the responsivity of ~41.9 mA/W under 360 nm at a bias voltage of −0.5 V and has a linear response to the ultraviolet (UV) light in a wide light intensity range of 0.1–10 ⁴ mW/cm ² . The response time decreased as the light intensity rose from 3 mW/cm ² to 5 W/cm ² and then leveled off at higher light intensity (>100 mW/cm ² ), which is about 0.25 ms. The photodetector −3-dB cutoff is ~3400 Hz at $\boldsymbol {\lambda } = 360$ nm and light intensity = 100 mW/cm ² . Besides, the detector can respond to the UV light from 260 to 360 nm and the peak responsivity is ~78 mA/W at 320 nm. The analysis results have reference values for the development of an innovative 4H-SiC UV photodetector to some extent.

High-sensitivity ultraviolet (UV) photoelectric detection technology is significant in UV communication, missile tail flame radiation detection, and fire early warning. This article utilized a 4H-SiC phototransistor detector to respond to weak UV light. A corresponding detection circuit system was developed to convert the photogenerated analog current signal to a digital voltage signal and transmit the digital signal to the host computer. A trans-impedance amplifier amplifies and transfers the weak photocurrent into a large voltage signal, which possesses a stronger antijamming ability. The analog-to-digital converter converts the analog voltage signal into a digital signal for convenient transmission in the following circuits. A universal serial bus interface module transmits the digital signal to the host computer using a serial transmission method with a field-programmable gate array controlling the timing. A graphical software interface based on LabVIEW was developed to display the collected digital data that stand for real-time UV intensity. Monitoring and recording the weak optical power of the UV light emitted by candlelight can be realized via the system. The UV power density range was between 50 nW/cm $^{\text{2}}$ and 3 $\mu$ W/cm $^{\text{2}}$ , and the corresponding output voltages ranged from 0.095 to 3.45 V. Compared with traditional high-voltage biased p-i-n avalanche diode detection system, the flame detection system demonstrated in this article was based on a 4H-SiC phototransistor, which has the advantages of low voltage and high stability.

A ZnO nanomaterial-based surface acoustic wave (SAW) ultraviolet (UV) detector is highly desirable for UV radiation detection due to its high sensitivity. In this work, firstly the ZnO nanomaterial-based SAW UV detectors operating at three different frequencies (∼50, ∼100 and ∼200 MHz) were fabricated. Then, four ZnO nanomaterial sensing layers with different thicknesses were synthesized on the SAW UV detectors operating at ∼200 MHz. The morphology, crystallization and photoluminescence of ZnO nanomaterial sensing layers were characterized using the scanning electron microscopy, transmission electron microscopy, x-ray diffraction and fluorescence spectrometer, respectively. The SAW UV detectors based on different operating frequencies and ZnO nanomaterial sensing layer's thicknesses were exposed under UV illumination at a wavelength of 365 nm and their UV responses were measured. The experimental results indicate that the frequency shift of ZnO nanomaterial-based SAW UV detector can be significantly improved by increasing operating frequency or ZnO nanomaterial sensing layer's thickness. Furthermore, the detectors exhibit good selectivity of UV illumination, an ultrahigh UV sensitivity of about 9.6 ppm (µW cm−2)−1 and fast transient properties. The experimental results agree well with the acousto-electric effect theory. What deserves to be noted is that, under a UV intensity of 150 µW cm−2, the frequency shift of the SAW UV detector operating at ∼50 MHz with a thin ZnO nanomaterial sensing layer was only ∼50 kHz while that of the SAW UV detector operating at ∼200 MHz with a thick ZnO nanomaterial sensing layer could reach ∼292 kHz. These results suggest the huge potential applications of ultra-sensitive ZnO nanomaterial-based SAW UV detectors for remote wireless UV and radiation monitoring.

A Lamb wave is a guided wave that propagates within plate-like structures, with its vibration mode resulting from the coupling of a longitudinal wave and a shear vertical wave, which can be applied in sensors, filters, and frequency control devices. The working principle of Lamb wave sensors relies on the excitation and propagation of this guided wave within piezoelectric material. Lamb wave sensors exhibit significant advantages in various sensing applications due to their unique wave characteristics and design flexibility. Compared to traditional surface acoustic wave (SAW) and bulk acoustic wave (BAW) sensors, Lamb wave sensors can not only achieve higher frequencies and quality factors in smaller dimensions but also exhibit superior integration and multifunctionality. In this paper, we briefly introduce Lamb wave sensors, summarizing methods for enhancing their sensitivity through optimizing electrode configurations and adjusting piezoelectric thin plate structures. Furthermore, this paper systematically explores the development of Lamb wave sensors in various sensing applications and provides new insights into their future development.