Modulation Transfer Function Measurements by Electron-Beam-Induced Current of HgCdTe Planar Diode with Small Pitch and High Operating Temperature

Abstract

Planar diodes usually present a potentially degraded modulation transfer function (MTF) for small pixels due to lateral diffusion of photo-generated carriers in the absorption layer. Indeed, in such a configuration, there is no physical separation between adjacent pixels, and when dealing with high operating temperature (HOT), the diffusion length might be much longer than the pixel size due to the long lifetime required for small dark current. For the p-on-n HgCdTe (MCT) diodes performed at LETI-Lynred, this diffusion length is much larger than the pixel pitch targeted at 7.5 µm. MTF optimization is therefore necessary to obtain the full image resolution targeted by the pitch array. However, MTF characterization of such small pixels is not an easy task in the mid-wave infrared (MWIR) range, as the pixel size is close to the wavelength due to the diffraction limit. This work confirms a strong interest in using EBIC for MTF measurement of small pixel pitches, with a systematic study of 7.5 µm pixel pitch with different designs aimed at optimizing MTF. For an optimized diode of the new generation p-on-n technology, the measured MTF at Nyquist is 55%, value close to the ideal pixel.