High speed photodetectors are most sophisticated optoelectronic devices, because it has high photo sensitivity, low noise, high conversion efficiency and allow a large wavelength range of detection from 750 nm to 1.3-1.55 pm in the optical communication system. These photodetector is used as an optical receiver which transforms the energy of optical radiation such as infrared, visible or ultraviolet into the electrical signal that is convenient for measurement. Since the last decade, the electro-optical characterisation of photodetectors has been investigated to improve their performance and price. In this paper, we are going to discuss the characterisation of the two different type infrared photodectors based on nanowire that we have worked on our project. One photodetector is p- n nanowire structure, and another is p-i-n structure. Both photodetectors is worked based on internal photoelectric effect and on the theory of p-n junction. We investigated the detector performance at 77K-300K temperature corresponding with wavelength in darkness and under illumination as regarding breakdown voltage, sensitivity, and quantum efficiency. We have also compared the differences between the two photodetectors performance characteristics. © 2012 ACADEMY PUBLISHER.