Carrier transport mechanisms are investigated in InAs and InSb infrared photodiodes. The photodiodes were prepared by thermal diffusion of Cd and ion implantation of Be into InAs and InSb single-crystal substrates of n-type conductivity, respectively. The direct current was measured as a function of bias voltage and temperature. The excess tunneling current is observed in the investigated photodiodes at small forward bias voltages. Experimental proofs are obtained that dislocations are responsible for this current. A model for the tunneling current via dislocations is briefly discussed.