MTF-BASED APPROACH TO THE DETERMINATION OF THE BULK DIFFUSION LENGTH OF PHOTOGENERATED CHARGE CARRIERS IN THE ABSORBER MATERIAL OF MCT-BASED INFRARED FOCAL PLANE ARRAYS
V.V. Vasiliev, A.V. Vishnyakov, G.Yu. Sidorov, V.A. Stuchinsky
Rzhanov Institute of Semiconductor Physics, Russian Academy of Sciences, Siberian Branch, Novosibirsk, Russia
Keywords: focal-plane-array (FPA) detector, photodiode, spot-scan profile, iffusion length, modulation transfer function (MTF), line spread function (LSF), mercury-cadmium-tellurium (MCT), Monte Carlo simulation
Abstract
A new method for estimating the bulk diffusion length Ldif of photogenerated charge carriers in the absorber material of mercury-cadmium-tellurium-based infrared focal plane arrays (MCT-based IR FPAs) is proposed. The method is based on the analysis of the modulation transfer function (MTF) of IR FPA detectors in normal operation and in operation with reduced gate voltage of input pixel field-effect transistors, when the built-in junction barriers of FPA diodes turn out to be reduced, and multiple re-emission of mutually induced microscopic currents of neighbor photodiodes takes place. The proposed mathematical model for the MTF of MCT-based FPAs assuming the capture of emitted electrons by the nearest FPA pixels provides an adequate description to the experimentally observed behavior of the diode-array MTF during the transition of FPA to the latter operation mode. This fact is illustrated in the article with the example of a 30-μm pitch FPA with ~10×10-μm diode sizes and 6-μm absorber-layer thickness. The coefficient of transfer of the injection current of a forward-biased photodiode to an adjacent pixel, which appears in the model, depends on the geometrical parameters of the diode array and on the length Ldif , and it can be used for determining this length.
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