Analysis of crosstalk in HgCdTe p-on-n heterojunction photovoltaic infrared sensing arrays

In this paper, an experimental and theoretical study is carried out of crosstalk between nearest-neighbor devices within a backside-illuminated linear HgCdTe photovoltaic infrared sensing array. The dominant form of crosstalk that occurs in high performance photovoltaic arrays is associated with photogenerated minority carriers that diffuse laterally between adjacent devices within the array. To measure crosstalk, a scanning laser microscope is used to obtain a spatial map of spot-scan photoresponse at a temperature of 80K for individual p-on-n photovoltaic devices within the linear array. These experimental results are compared to calculations performed on a commercial two-dimensional device simulation package. The crosstalk measurements and calculations presented in this paper include results on mid-wavelength infrared planar device structures, as well as long-wavelength infrared mesa-isolated devices, which give measured crosstalk values of 6.2 and 8.3%, respectively. The results indicate that the device simulations are in good agreement with experimental results. Further simulations are carried out to determine the sensitivity of crosstalk to various material and device parameters such as epitaxial layer thickness (7 to 25 µm), illumination wavelength (1.047 to 11.0 µm), minority carrier diffusion length (8 to 90 µm), and diode pitch. It is found that the dominant feature influencing the value of crosstalk is the distance between the region of photogeneration and the collecting p-n junction.