The results of the HgCdTe p + on n long wavelength hetero junction infrared focal plane arrays were presented. HgCdTe p + on n hetero junction material was grown by molecular beam epitaxy(MBE) and in situ doping, and HgCdTe p + on n hetero junction infrared focal plane arrays were fabricated by the process of wet etching, side wall passivation, side wall matelization, indium bump fabrication and hybridization etc. According to the I V experiments and the dark current mechanism, the effect of all kinds of dark current was calculated and analyzed. The spectral response and detectivity of the device were also measured.