Determination of charge-carrier diffusion length in the photosensing layer of HgCdTe n-on-p photovoltaic infrared focal plane array detectors

Abstract

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Determination of the Bulk and Local Diffusion-Length Values of Charge Carriers in MCT Films and in the Absorber Layers of MCT-Based Photovoltaic IR FPA Detectors

“…At a high level of diode photocurrents j ph , however, the latter approach becomes invalid because of a decreased value of l d eff . In the present paper, we extend the analysis [18] of the diffusion process of charge carriers in the photosensitive film of FPA detectors to the case of large diode photocurrents j ph . We show that, following the determination of the length l d by the method [18], treatment of spot-scan profiles S(x) measured at large diode photocurrents within a simple 2D diffusion model makes it possible to determine the local effective diffusion length l d eff of minority carriers in the film region under FPA diodes in normal operational regime of the photodetector.…”

“…In the present paper, we extend the analysis [18] of the diffusion process of charge carriers in the photosensitive film of FPA detectors to the case of large diode photocurrents j ph . We show that, following the determination of the length l d by the method [18], treatment of spot-scan profiles S(x) measured at large diode photocurrents within a simple 2D diffusion model makes it possible to determine the local effective diffusion length l d eff of minority carriers in the film region under FPA diodes in normal operational regime of the photodetector. In this way, we for the first time give a complete analysis of the charge-carrier diffusion process in a photosensitive film of MCT IR FPA detectors at arbitrary diode photocurrents.…”

“…A good strategy toward diminishing the influence of measuring circuits on the distribution of charge carriers in the absorber layer consists in decreasing the level of registered diode photocurrents j ph . By following this strategy, we have recently proposed a new method for determining the bulk diffusion length of charge carriers l d in the absorber layer of MCT IR FPA detectors [18]. In the new method, the spot-scan technique was implemented at low levels of diode photocurrents j ph , and the bulk diffusion length of charge carriers in the photosensitive film l d was proposed to be determined as the extreme value of their "spatially averaged" effective diffusion length l d eff for j ph → 0.…”

“…In the new method, the spot-scan technique was implemented at low levels of diode photocurrents j ph , and the bulk diffusion length of charge carriers in the photosensitive film l d was proposed to be determined as the extreme value of their "spatially averaged" effective diffusion length l d eff for j ph → 0. The length l d eff at low diode photocurrents j ph having been sufficiently large, the diffusion of photogenerated charge carriers in the photosensitive film of examined detectors was analyzed in [18] within a continuum approach. At a high level of diode photocurrents j ph , however, the latter approach becomes invalid because of a decreased value of l d eff .…”

Analysis of local charge-carrier diffusion length values in the photosensing film of photovoltaic HgCdTe FPA photodetectors

“…diffusion length of charge carriers is equal to the bulk diffusion length of charge carriers in the HgCdTe material of the absorber layer; the latter length was previously determined in 1 . Simultaneously, in the film region under photodiodes a decreased value of l d eff , defined by a certain local value of k, k ph , is assumed (…”