Design of practically realizable unipolar HgCdTe nBn photodetectors has been studied in detail by numerical analysis. The simulations reported herein reveal that, by optimization of barrier doping, dark current levels can be reduced and collection efficiency substantially improved. It is shown that p-type doping of the barrier layer can significantly reduce the effective potential barrier arising from the valence band offset between the absorber and barrier regions, thus enabling HgCdTe nBn detector operation under near zero-bias conditions. However, relatively high electric fields in the space charge regions near the barrier/absorber interface result in enhanced trap-assisted Shockley–Read–Hall thermal generation. Our calculations indicate that nBn HgCdTe detectors with barriers engineered by use of HgTe/Hg_0.05Cd_0.95Te superlattices have, potentially, substantially better valence band alignment without the need for p-type doping.

An enhanced original computer program is applied to explain in detail the current-voltage characteristics of n-on-p long wavelength infrared HgCdTe photodiodes. The computer program solves the system of nonlinear continuity equations for carriers and Poisson equations. In the model ideal diode diffusion, generation-recombination, band-to-band tunneling, trap-assisted tunneling, and impact ionization are included as potential limiting mechanisms in the photodiodes. It is a clearly explained influence of Hg-vacancy doping and extrinsic doping of an active device region on dark current-voltage characteristics and an $R_{0}A$ product of HgCdTe photodiodes in a wide region of temperature and wavelengths. Special attention is directed to the dependence of tunneling probability on the shape of potential barrier with in an depletion region. The theoretical predictions are compared with experimental data of high quantity photodiodes published in the available literature.

The effect of an abrupt $\mathrm{Cd}\mathrm{Te}∕\mathrm{Hg}\mathrm{Cd}\mathrm{Te}$ passivation heterointerface on generation recombination and dark currents in $n$ -on-$p$ midwave infrared photodiodes with $5.2\text{-}\mu \mathrm{m}$ cut-off wavelength has been investigated. Experimentally, it was observed that the zero-bias-dynamic resistance, $R_0$ , at low temperatures scales with the perimeter of the $n$ -on-$p$ junction, rather than with the junction area, suggesting that surface effects are dominant. The diode current–voltage characteristics at low temperatures indicate significant contributions from tunneling effects, which is the dominant leakage current mechanism for reverse bias greater than approximately $30\mathrm{mV}$ . These two observations suggest that the region where the junction terminates at the $\mathrm{Cd}\mathrm{Te}∕\mathrm{Hg}\mathrm{Cd}\mathrm{Te}$ abrupt interface is responsible for the above effects. A two-dimensional model has been developed to investigate the dark current mechanisms in the vicinity of the junction termination at $\mathrm{Cd}\mathrm{Te}∕\mathrm{Hg}\mathrm{Cd}\mathrm{Te}$ interface, which also takes into account the effect of dislocations on generation-recombination processes. Calculated profiles of the energy bands and electric field along different cross sections of the photodiode indicate that the electric field achieves a maximum value of the order of mid $-{10}^5\mathrm{V}∕\mathrm{cm}$ in the region where the junction terminates at the $\mathrm{Cd}\mathrm{Te}∕\mathrm{Hg}\mathrm{Cd}\mathrm{Te}$ interface. The presence of such a high localized electric field in this area decreases the ionization energy of trap levels in the band gap and, hence, increases efficiency of the Shockley–Read–Hall generation-recombination processes. In addition to diffusion, generation recombination, and trap-assisted tunneling mechanisms, the calculations of dynamic resistance include Poole–Frenkel and phonon-trap-assisted tunneling effects. The best fit to the zero bias dynamic resistance versus temperature results has been obtained using an aerial dislocation density in the bulk of the HgCdTe layer equal to ${10}^6{\mathrm{cm}}^{-2}$ . Although the direct band-to-band tunneling and impact ionization processes were also considered, their contributions are shown to be insignificant.

Comprehensive study of the bulk generation-recombination mechanisms and the carrier lifetime in long wavelength and mid wavelength infrared indium-doped as well as arsenic- and mercury vacancies-doped HgCdTe ternary alloys at liquid nitrogen temperature has been done. The excess minority carrier lifetime in HgCdTe materials has been calculated by solving the set of non-linear transport equations under conditions of small deviation from equilibrium. The results of numerical calculations of the carrier lifetime determined by the Auger 1, Auger 7, and Shockley-Read-Hall mechanisms related to mercury vacancies have been compared with experimental data available in the literature. We re-examine the carrier lifetime, including the impact of the electrical screening on Coulomb interaction of carriers in the Auger process to explain certain inconsistency between theoretical prediction and experimental data especially in highly doped p-type HgCdTe material. Moreover, the marginal significance of the interband radiative recombination has been indicated.