The paper presents results of modelling the photosensitivity of an IR photodiode based on HgCdTe of spatially variable composition. It is assumed that in the front p-base region energy gap linearly decreases in the direction to metallurgical edge of the p-n junction, whereas in the n-base energy gap firstly does not change with coordinate and then increases towards the rear contact.

For the photodiode with the proposed form of energy band diagram we have developed an analytical model of photocarrier transport that allows one to calculate the photosensitivity spectra depending on the band gap gradients in both base regions, thicknesses of base regions and photocarrier surface recombination velocity at the illuminated plane of the photodiode.

It is shown that due to internal quasi-electric field, which acts in the front base region there takes place a reduction of influence of photocarrier surface recombination upon the photosensitivity, as well as an increase of the collection coefficient of photocarriers. Presence of homogeneous region adjoining the p-n junction gives rise to increasing the absorption of photons what results in increasing the quantum efficiency of the photodiode. Besides, such a photodiode is characterized by widen range of the photosensitivity and reduced dark current.

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1. Modeling of photoresistors based on semiconductor multilayer variable-GAP structures