In this paper an analytical modeling and 2D numerical simulation of P +-Hg0.69Cd0.31Te/ n-Hg0.78Cd 0.22Te/CdZnTe single heterojunction photodetector using the commercially available atlasTM package from SILVACO® International for long-wavelength free space optical communication has been reported. The photodetector has been studied with respect to energy band diagram, electric field profile, doping profile, dark current, resistance area product, quantum efficiency, spectral response, responsivity, and detectivity by an analytical method using closed form equations. The results obtained on the basis of the analytical model have been compared and contrasted with the simulated results using atlasTM. The photodetector exhibits high values of quantum efficiency ∼80, responsivity ∼6.75 A/W, specific detectivity ∼2.25 × 1011 mHz1/2W-1 at wavelength10.6 μm, and dark current of the order of 10-11 A. The estimated noise equivalent power (NEP) is of the order of 1 × 10 -17 W. © 2011 American Institute of Physics.