# Research on Fast Detection Technology of Dark Currents in a Ge-Si Detector Array
## 1 Introduction
The weak light detection limit could be as low as \(-\)35 dBm, while the bias voltage was only 7 V [24]. The University of Heriot-Watt in the UK conducted research on single-photon Ge-Si APDs (avalanche photodiodes). In 2013, they produced a traditional vertical-structure Ge-Si APD, which achieved a single-photon detection function in the Geiger mode at the low temperature of 100 K [25]. The Sandia National Laboratory in the United States produced a novel horizontal-structure Ge-Si APD, which improved the single-photon detection efficiency to 5.27%, providing a solid technical foundation for implementing ultra-long-range LiDAR [26]. The Singapore Institute of Microelectronics first reported the research results of Ge-Si APD arrays forming photomultiplier tubes at the 2019 OFC International Conference [27], and the photoelectric detection efficiency between array units showed good consistency. However, the dark current was still relatively high, and the dark current near the breakdown voltage of the single-transistor APD also reached the \(\upmu\)A level. Academician [PERSON]'s research group at the Institute of Semiconductors of the Chinese Academy of Sciences studied the epitaxial growth of Ge on monocrystalline silicon using ultra-high-vacuum CVD (chemical vapor deposition). Recently, extensive research has been conducted on Ge-Sn alloys [28]. Xiamen University studied upper and lower DBR (distributed Bragg reflector) microcavity-enhanced germanium photodetectors with similar surface emission structures [29], but the photoelectric conversion efficiency was slightly low. The [PERSON] research group at Peking University studied a short-cavity Ge-Si photodetector with an enhanced horizontal DBR reflection of 5 \(\upmu\)m. The long absorption region achieved a photoelectric conversion efficiency of 0.72 A/W, the 3 dB bandwidth reached 31.7 GHz, and the dark current was only 7 nA [30]. In response to the urgent demand for photodetectors in the field of LiDAR, we conducted research on PIN-type Ge-Si photodetectors. By optimizing the doping structure and concentration design, we effectively suppressed the electric field distributed at Ge and Si heterojunctions and prepared a low-dark-current and high-responsiveness 32 \(\times\) 32-pixel Ge-Si photodetector array. In order to test the performance of the detector array, we needed to design a fast dark current detection system. The system quickly scans each pixel of the array, applies different bias voltages to each pixel, and reads the different dark currents generated by the pixel. The photocurrent generated by the detector includes the sum of the photogenerated current and the dark current. If the proportion of dark current is large, the photocurrent cannot effectively characterize the photoelectric conversion performance of the detector, and the dark current of the detector is inversely proportional to its optical response characteristics. Usually, the dark current of photodetectors is at the nanoampere level and has a large range of variation. It is generally necessary to use high-gain preamplifier circuits and a range of automatic conversion circuits to achieve this [31, 32, 33]. For detector arrays, it is necessary to design corresponding scanning circuits to select pixels [34], similar to the imaging principle of charge-coupled device (CCD) cameras. Based on the characteristics of Ge-Si detector arrays and the design principles of detection circuits, our detection system can quickly detect the dark current distribution of the entire array and locate damaged pixels, providing us with testing and verification methods for device design. It can be used for the rapid detection of dark currents in larger detector arrays in the future.