The performance of infrared InAs homojunction and heterojunction photodiodes (PD) and possibilities of its improvement are analyzed both theoretically and experimentally. The figures of merit such as the resistance-area product <i>R<sub>0</sub>A</i>, the carrier lifetime and the quantum efficiency are studied. The excess carrier lifetime in InAs are calculated for radiative and Auger recombination mechanisms using three- and four-band Kane model. Theoretical limit of threshold parameters in InAs-based photodiodes is calculated for intrinsic (radiative and Auger) recombination processes. The diffused PD were prepared by short-term cadmium diffusion into substrates with <i>n</i>-type conductivity. In the investigated PD the total dark current is determined by the diffusion carrier transport mechanism at room temperature. Experimentally proved that heterojunction PD <i>p</i><sup>+</sup>-InAsSbP/<i>n</i>-InAs can be more effective as sensitive element in gas sensors operated at room temperature in comparison with commercially available PD. Experimentally proved that heterojunction PD p+-InAsSbP/n-InAs can be more effective as sensitive element in gas sensors operated at room temperature in comparison with commercially available PD. Their threshold parameters (current sensitivity and detectivity) have approximately the same values as in commercially available photodiodes, but they have higher values of the resistance-area product.