Effect of trapped charges and ionic charges distribution on n+-on-p HgCdTe photodiode properties

The HgCdTe Photodiode is the most basic and important unit of HgCdTe IRFPA (Infra-red focal plane array) detectors, which have been widely used in the fields of security, fire protection, remote sensing and deep space detection. For HgCdTe IRFPA, the trapped charges of the HgCdTe material and the ionic charges introduced during the preparation process are the factors, other than environmental stress, that have the greatest impact on IRFPA performance. The trapped charges come from the trap energy level in the HgCdTe material, which exist during the crystal growth process and can be improved by adjusting the growth conditions, but it cannot be completely avoided. The ionic charges introduced during the process are generally concentrated at the interface and surface of the HgCdTe material, which can be reduced by process improvement, but cannot be completely avoided. In order to analyze the mechanism of multiple charges affecting the HgCdTe detector performance, a type of n+ -on-p HgCdTe Photodiode is selected as the object of this work, and the effects of the concentration and distribution of charges on the carrier distribution and energy band structure of the n+ -on-p HgCdTe are analyzed in detail. The introduction of additional net charge relative to an ideal n+ -on-p HgCdTe Photodiode leads to the aggregation or scavenging of local carriers and affects the energy band structure near the charge, creating additional potential barriers or potential wells, which is likely to cause device degradation. On this basis, the optoelectronic properties of the HgCdTe Photodiode have been investigated under infrared radiation at a wavelength of 9.5 μm, as the light I–V characteristics, the dynamic resistance–voltage characteristics, band structure and carrier density distribution. According to the results of this work, the quasi-fixed charges introduced by defects or contamination will directly affect the generation rate of photogenerated carriers and affect the I–V and R–V characteristics of the HgCdTe Photodiode, leading to phenomena such as rising dark currents, decreasing spectral response, and decreasing quantum efficiency.