Electrical Crosstalk of Photovoltaic HgCdTe Array Detector

Shuai Qiao; Rui Wang; Xiaocheng Hou

doi:10.3788/AOS221555

Abstract

Results and Discussions We have discovered that there is a crosstalk phenomenon in pixels far from the irradiation area in the experiment of a 512×1 linear HgCdTe array detector irradiated by a pulsed laser. COMSOL Multiphysics finite element simulation software is used to simulate the carrier concentration distribution in the chip (Fig. 7) and the change of carrier concentration in the center of each pixel with the laser irradiation time (Fig. 8) to study the mechanism of the device's crosstalk phenomenon. It is discovered that the crosstalk of pixels close to the irradiation area is directly caused by the lateral diffusion of photogenerated carriers along the array alignment, while it has little effect on pixels far from the irradiation area. By simulating the direction of the electric field in the chip (Fig. 9) and the common electrode voltage (Fig. 10), the reason for the response of pixels far from the irradiation area can be fundamentally explained. It is discovered that some photogenerated carriers move to the common electrode under the action of the electric field, which results in the decrease in the common electrode voltage and the rise in all pixels' responses. The measure of trench isolation to suppress crosstalk (Fig. 11) is established based on the understanding of the device's electrical crosstalk generation mechanism, and simulation results (Fig. 12) show that the measure has significantly suppressed electrical crosstalk.Objective

The crosstalk effect has always been one of the challenging issues in detector performance. Due to the increase in the detector array scale and the decrease in pixel center distance, the spatial resolution of the detectors greatly improves, and the crosstalk effect becomes more obvious, with a significant impact on the performance of the detectors. The crosstalk effect considers the problem of signals produced in the target pixel being interfered by some factors and makes other pixels to produce response signals. Crosstalk can be divided into optical crosstalk and electrical crosstalk based on different generation mechanisms. Optical crosstalk refers to the optical factors such as light reflection, refraction, and diffraction that make signals appear in other pixels. Electrical crosstalk refers to the signal response of other pixels due to the diffusion of photogenerated carriers. HgCdTe detector is widely used in both civil and military fields because of its high sensitivity, broad coverage band range, and other advantages. The crosstalk phenomenon exists in array HgCdTe detectors under continuous laser or pulsed laser irradiation, according to a lot of recent studies on the laser irradiation effect of HgCdTe array detectors. Previous research has shown that optical crosstalk is not the primary mechanism driving the response of unirradiated pixels in array devices, and it is inferred that this response is caused by electrical crosstalk. However, the conclusion has not been verified systematically. In this study, a linear HgCdTe array detector is used as the research subject, and we try to explore the mechanism and degree of electrical crosstalk as well as practical strategies for reducing it. In addition, we expect that these findings can have a certain reference value for improving the performance of detectors.

Methods

We use COMSOL Multiphysics finite element simulation software to establish a three-dimensional simulation model of a pulsed laser irradiation detector chip and study the crosstalk problem in a laser irradiation linear HgCdTe array detector experiment. Firstly, on the basis of the mechanism of electrical crosstalk caused by the diffusion of photogenerated carriers, the distribution of carrier concentration in the chip under laser irradiation with different energy densities is simulated. It is discovered that the diffusion of photogenerated carriers has a slight direct impact on pixels that are far from the irradiation area. Secondly, the direction of the electric field in the chip is simulated during laser irradiation, and it is discovered that the electric field under laser irradiation points to the common electrode. This electric field will make some photogenerated carriers to move to the common electrode, which will change its voltage and affect the output of the detector. Additionally, the common electrode voltage of the chip is simulated under different energies of laser irradiation, which confirms the conclusion that a decrease in the common electrode voltage can result in a response from every pixel of the detector. Finally, a measure to suppress the crosstalk is suggested. In other words, a three-dimensional isolation trench is designed based on the principle of limiting or reducing the lateral diffusion of photogenerated carriers, and the effect of the suppression of crosstalk is verified by simulation.

Conclusions

In view of the crosstalk phenomenon in the laser irradiation linear HgCdTe array detector experiment, the mechanism of the crosstalk is revealed by simulating the carrier concentration distribution, photocurrent, electric field direction, and common electrode voltage in the laser irradiation photosensitive chip in this paper. Research shows that the lateral diffusion of photogenerated carriers along the array alignment directly contributes to the crosstalk of pixels close to the irradiation area, while it has little effect on pixels far from the irradiation area. There is an electric field pointing to the common electrode of chip when it is irradiated by the laser. Under the influence of this electric field, some photogenerated carriers move to the common electrode, which results in the voltage reduction of the common electrode, and then all of the detector's pixels rise in response. In addition, the measure of electrical crosstalk suppression by trench isolation, which has a significant influence on crosstalk suppression, is proposed based on the mechanism of electrical crosstalk generated by the lateral diffusion of carriers. The problem of crosstalk brought by the common electrode voltage variation can be resolved by changing the circuit design or correcting the output signal. It is necessary to conduct more research on the specific measures.