Study On Capacitance Characteristics Of Photosensitive Elements In HgCdTe Infrared Focal Plane

HgCdTe is one of the most promising alloy materials in the field of infrared detection.As narrow band-gap semiconductors,HgCdTe materials are often used in mid-long wave infrared detection,especially in the atmospheric windows of3-5μm and 8-12μm,their detector performance is closely related to the capacitance of HgCdTe.It is difficult to measure the capacitance of HgCdTe-PN junction because it is so small,and the HgCdTe capacitance reported in the previous literature only gives the results of capacitance size directly,without any introduction to the process of testing and the comparison of the capacitance with other detectors.In contrast,this paper introduced the principle of measuring the capacitance of HgCdTe in detail,analyzed and calibrated the parasitic capacitance,and finally gave the error analysis.Also the capacitance of HgCdTe detector in this paper is compared with other detectors,and the carrier concentration and the corresponding depth in the junction region are calculated,which are in agreement with the experimental data of delamination Hall.This paper focuses on the capacitance of mercury cadmium telluride.The main contents are as follows:（1）In this paper,the method of measuring the capacitance of HgCdTe device by Dewar at liquid nitrogen temperature is reported,and the parasitic capacitance of the instrument and the parasitic capacitance of Dewar are calibrated.The data of carrier concentration and depth near the junction region of PN are calculated by using the C-V test results.The capacitance at zero bias voltage is 92.8 pF and the capacitance density is 5.13×10⁴ pF·cm^-2.With the increase of reverse bias voltage,the width of depletion layer increases and the capacitance decreases.Considering the parasitic capacitance error of instrument,the final capacitance error rate is 0.32%to 0.42%.The results show that the depletion layer width is 0.28μm at zero bias,and the corresponding N-region carrier concentration is 6.07×10¹⁵cm^-3.With the increase of the N-region depth Wn,the carrier concentration in the N-region increases,which is consistent with the structure of the n-n/p device in this paper.（2）HgCdTe avalanche photodiode（APD）device is fabricated and analyzed,and the results are compared with HgCdTe conventional PN junction device.The capacitance of HgCdTe APD device at zero bias voltage of HgCdTe device 2 is11.3pF.The capacitance of HgCdTe device is significantly lower than that of92.8pF of HgCdTe device No.1 under the same area.Considering the parasitic capacitance error of instrument,the final capacitance error rate is 2.65%to3.31%.The results show that the depletion layer width is 2.33μm at zero bias,and the corresponding N-region carrier concentration is 3.47×10¹⁴ cm^-33 for APD device 2.Comparing the conventional device with the APD device,APD’s width of the depletion layer is much larger than that of the conventional device,which indicates that annealing can widen the depletion layer.However,the N-region carrier concentration of APD devices is lower,which also shows that annealing can lead to the diffusion of mercury gap and the decrease of N-region carrier concentration.（3）HgCdTe APD devices with different annealing conditions were fabricated and the measured results were compared.The experimental results show that annealing can widen the depletion layer of APD and obtain a smaller junction capacitance.And within a certain range the longer the annealing time is,the smaller junction capacitance and carrier concentration in N region is.Compared with the traditional delamination Hall experiment,the carrier concentration and the corresponding junction depth can be obtained by measuring the C-V curve and calculating the C-V curve,which is simpler and more convenient than the traditional delamination Hall experiment.It has good significance in practical research（for example,the gain-voltage curve of APD devices can be calculated by carrier concentration and depletion layer width,etc.）.