Trap assisted tunnelling via traps located at dislocation cores as well as mercury vacancies are considered as the mechanisms of enhanced thermal generation of charge carriers in reverse-biased MWIR HgCdTe photodiodes operating with Peltier cooling. Field-induced reduction of trap activation energies increases thermal generation and creates conditions for large tunnelling currents. The model for LWIR devices published previously in Ref. [20], also explain experimental current-voltage characteristics of the MWIR photodiodes assuming great misfit dislocation density at graded gap interfaces between absorber and contact regions. (C) 2011 Elsevier Ltd. All rights reserved.