抄録
We have made improvements on the modulation transfer function (MTF) for 256 X 256-element HgCdTe back-illuminated infrared focal plane arrays (IRFPA) in the 8 to 10 pm band. In our approach, each HgCdTe photodiode is surrounded by a ditch structure to control the effective photosensitivity profile. In MTF measurements with a four-bar pattern, an IRFPA with a 9 pm deep ditch structure exhibited an improved MTF of 0.39 at the Nyquist frequency, which is about twice that of conventional planar diode structures. Using a two-dimensional model of minority-carrier diffusion in a HgCdTe epilayer, we analytically verified that the MTF increases and that the photocurrent decreases slightly as the ditch depth increases. These results suggest that using the ditch structure to control MTF is effective for resolving the detail of infrared images for back-illuminated IRFPAs.
