Quantum dot base infrared detectors have many advantages such as lower dark current, higher operating temperature, higher photoconductive gain, and broader infrared response. For this reason, we have studied a pyramidal shape quantum-dot infrared photodetector (QDIP) in which the different mechanisms of noise and dark current, the effects of QD size variation, the temperature, and applied electric field are considered. Self-assembled In0.3Ga0.7As / GaAs pyramidal shape quantum dots have been considered and optical properties in the conduction band using effective mass Schrodinger equation by the finite-difference time-domain (FDTD) method have been analyzed. Finally, the detectivity calculated as functions of the applied electrical field and temperature. For example, at the T = 77 ° K and E = 2 kV / cm, the detectivity is 3 × 1013 cmHz − 1/2 / W.