# Research on Fast Detection Technology of Dark Currents in a Ge-Si Detector Array
## 3 Array Test and Data Analysis  
We designed detector arrays of four different sizes, A, B, C, and D. The target surface of array A is 2.5 cm \(\times\) 2.5 cm, that of array B is 2.0 cm \(\times\) 2.0 cm, that of array C is 1.5 cm \(\times\) 1.5 cm, and that of array D is 1.0 cm \(\times\) 1.0 cm, as shown in Figure 8. The photosensitive surface of a pixel accounts for about half of the whole pixel area, that is, the fill factor of all devices is 0.5. We needed to detect dark current on these four arrays and determine the distribution of dark current and pixel consistency under different sizes, ultimately guiding us in device design. Figure 7: Hardware physical diagram of the detection system. Firstly, we measured a single pixel's bias voltage-dark current curve, as shown in Figure 9. The voltage scanning range was \(-\)3500 mV\(\rightarrow\)+100 mV, and the step voltage was 50 mV. As shown in Figure 9, the bias voltage-dark current curve of the first-row and first-column pixels of device A was consistent with the theoretical curve in Figure 2.  
Furthermore, we measured all dark currents in the device and determined their distribution characteristics. Figure 10 shows the two-dimensional histogram of the dark current distribution of device A, and Figure 10 shows the two-dimensional histogram of the dark current distribution at the bias voltages \(-\)2.5 V, \(-\)2.0 V, \(-\)1.5 V, \(-\)1.0 V, and \(-\)0.5 V. The higher part of the histogram in the figure shows a large and abnormal dark current. To quantify the array damage, we counted the number of pixels \(>\) 10 times the average dark current and the number of pixels \(>\) five times the average dark current. Table 1 shows the measurement results. The number of pixels with device A \(>\) 10 times the average dark current was two, totaling 1024 pixels and accounting for 0.2%. The number of pixels with device A \(>\) five times the average dark current was nine, accounting for 0.9%. The pixel damage of device A was \(<\)1%, indicating a good performance. Our system can continuously detect device damage and quickly locate the position of damaged pixels, so we can respond to imaging applications through compensation in the later stage. Further, we measured the dark current and its distribution of devices A, B, C, and D, as shown in Table 2. According to the theoretical design, the smaller the pixel area, the smaller the average dark current. Figure 11a shows the average dark current values of devices A, B, C, and D when the bias voltages were \(-\)2.5 V, \(-\)2.0 V, \(-\)1.5 V, \(-\)1.0 V, and \(-\)0.5 V. The higher the reverse-bias voltage, the larger the average dark current. In theory, the average dark current is in the order A \(>\) B \(>\) C \(>\) D. In actual measurements, A \(>\) B \(>\) C \(\approx\) D was shown, and the pixel areas of devices C and D were not significantly different. All average dark currents were indistinguishable. The actual measurement was consistent with the theoretical analysis. Figure 8: PD array chips (**A**–**D**). Figure 9: The bias voltage–dark current curve of the pixel (the first-row and first-column pixels of device A). Figure 10: Histogram distribution of dark current test for PD array A. (**a**) Bias voltage \(=-2.5\) V. (**b**) Bias voltage \(=-2.0\) V. (**c**) Bias voltage \(=-1.5\) V. (**d**) Bias voltage \(=-1.0\) V. (**e**) Bias voltage \(=-0.5\) V.  
Figure 11b,c show the number of pixels with a bias voltage of \(-2.5\) V, \(-2.0\) V, \(-1.5\) V, \(-1.0\) V, and \(-0.5\) V for devices A, B, C, and D \(>10\) times the average dark current and five times the average dark current, respectively. All devices had a pixel damage rate \(<1\%\), indicating a good performance. Among them, device B had the most severe pixel damage and the worst performance, while device D had the least pixel damage and the best performance. The damage to devices A and C was relatively small and basically equivalent, and both had a good performance. The above measurement results can guide us in the design of Ge-Si detector array chips.