Fig. 1: Modified fully-depleted absorption, multiplication region HOT MWIR APD structure.

a Schematic diagram of HgCdTe MWIR avalanche photodiodes with fully depleted absorber layer, the material is composed of multiple layers of composition gradients. b The distribution of Cd composition and the corresponding wavelength at 80 K for proposed MFDAM APD, whose absorption region is a wide bandgap (refers to high composition) altered. The absorbed photon-generated electrons (two in conduction band) will go through the three processes: recombination occurs after absorption (one electron remains), drift to the multiplication region for impact ionization (two electrons in (d)), relaxation in collection region (one electron in (c) and two in (d)). The absorbed two photon-generated holes in the valence band will have no impact ionization happens. The blue and pink circles indicate electrons and holes, respectively. e Modeled electric field profile of the structure showing that the absorber layer is depleted due to the presence of a built-in electric field. This phenomenon arises from the energy differences between the conduction and valence bands caused by the interaction of materials with different bandgaps. The diffusion of carriers leads to band bending, resulting in a redistribution of carriers near the contact surface, which, in turn, forms a space charge region and generates an electric field at the interface. f The normalized spectrum response of the proposed MWIR MFDAM APD device at 80 K.