Infrared detectors can be used for a variety of applications such as: using in fiber-optic communications. Conventional technology for IR detectors is using p-i-n structure based on GaAs compound. This paper reports on the design and modeling of an IR detector using a p-i-n GaAs structure. Comsol software is used to simulate the model and the detector is discussed for terminal current, dopant profile, and energy band diagram. Finally, we have studied electric field according to layer depth under thickness, bias voltage, and field magnitude. we analyzed the electronic and optic behavior of IR detectors simultaneously and detection spectrum was obtained in terms of wavelength. پرونده مقاله