Recently, the University of Science and Technology of China, Zhang Jun and other joint Nanjing University, Lu Hai, Zhang Rong team in the direction of the ultraviolet band single-photon LIDAR has made new progress, through the design and preparation of single-photon avalanche photodiode based on 4H-SiC material, the development of active quenching active recovery readout circuit technology, developed a practical value of the ultraviolet semiconductor single-photon detector, using the detector for the first time to realize the single-photon differential absorption ozone lidar system, and realize the ozone concentration monitoring in the altitude range of 1~3.5km.
UV single-photon detection technology plays an important role in application scenarios such as atmospheric monitoring, tail flame detection, electric arc detection and fire warning. Photomultiplier tubes are traditional single-photon detector devices in the UV band, but they have the disadvantages of low sensitivity, short lifetime, magnetic field sensitivity, etc., and cannot work stably for a long period of time in harsh environments (high temperature, vibration, strong radiation). In contrast, the wide-band semiconductor 4H-SiC material, characterized by high thermal conductivity, high radiation resistance, high electron saturation drift rate, and stable performance, has significant material performance advantages in the development of new ultraviolet semiconductor single-photon detectors. However, for a long time, the performance index of single photon detectors based on this material is poor, especially the detection efficiency is very low and the dark count rate is very high, which makes this type of single photon detector has no practical value.
In recent years, a team from the University of Science and Technology of China (USTC) and Nanjing University (NU) has made a series of breakthroughs in the joint research on ultraviolet semiconductor single-photon detectors.2023, the team optimized the new tilted-table structure and preparation process of 4H-SiC single-photon avalanche photodiodes and developed passive-quenching and active-recovering readout circuit technology, and for the first time, developed a miniaturized 4H-SiC single-photon detector prototype of practical value, which was used as a prototype for the first time. single-photon detector prototype with a detection efficiency of 10.3% and a dark count rate of 133 kcps in the 266 nm band [Rev. Sci. Instrum. 94, 033101 (2023)]. Since then, the research team has utilized the detector to demonstrate the first single-pixel single-photon imaging experiment in the ultraviolet (UV) band, achieving single-photon imaging with an imaging resolution of 192 × 192 pixels and a frame rate of 4 fps at a received light intensity of about 6 pW.
Fig. 1. (a) 4H-SiC single-photon avalanche photodiode structure; (b) active quenching active recovery readout circuit
On this basis, the research team has continued to work on the performance index of 4H-SiC single-photon detectors. On the one hand, the single-photon detection efficiency of the device has been improved by iteratively optimizing the 4H-SiC single-photon avalanche photodiode structure and process; on the other hand, a new type of active-quenching active-recovery readout circuit has been developed for the 4H-SiC single-photon avalanche photodiode device, which has effectively suppressed the probability of detector back-pulsing and significantly improved the saturation count rate at the same time. After characterization, the new detector has a detection efficiency of 16.6% in the 266nm band, a dark count rate of 138kcps, a post-pulse probability of 2.7%, and a saturation count rate of 13Mcps, which basically meets the performance requirements of single-photon detectors for UV single-photon lidar applications.
The research team used the detector for the first time in the single-photon differential absorption ozone LIDAR system to carry out related applications, the LIDAR system will be 289nm and 316nm pulsed laser vertical emission into the atmosphere at the same time, due to the ozone molecules of the two wavelengths of the laser absorption coefficient of the two wavelengths of the laser, through the comparison of the two laser echo signal attenuation rate can be performed inversely the atmospheric concentration of ozone at different heights. In order to compare the data, the echo signals were divided into two paths and detected and inverted with the traditional photomultiplier tube and the new 4H-SiC single-photon detector, respectively, and the experimental results showed that the ozone concentration distributions in the range of 1~3.5km using the two detectors were highly coincident with the inverted performances. The above work provides a high-performance and highly environmentally tolerant practical solution for single-photon lidar in the UV band.
Fig. 2. single-photon differential absorption ozone lidar system. (a) Schematic diagram; (b) continuous observation of ozone concentration
