Analysis of charge-carrier diffusion in the photosensing films of HgCdTe infrared focal plane array photodetectors

Abstract

The lateral diffusion of minority charge carriers in the photosensitive films of photovoltaic HgCdTe infrared focal plane array (IR FPA) detectors with a continuous (without mesa insulation of the diodes) absorber layer was experimentally studied and analyzed. The experimental study was performed using the spot-scan technique, implemented by scanning a narrow strip-shaped illumination spot with a selected FPA diode at various levels of diode photocurrents in the detector. The local diffusion lengths of the charge carriers in the film regions beneath and outside the FPA diodes were estimated. The values obtained for the bulk diffusion length of minority carriers in the HgCdTe material of the examined middle-wave and long-wave IR FPA detectors were found to be in good agreement with previously reported data. Moreover, the estimated local diffusion length of minority carriers in the film region beneath the back-biased photodiodes proved to be consistent with a theoretical estimate of this length.