Long-wavelength (λc~12.5 μm) 256×1 infrared photodiode arrays based on liquid phase epitaxy (LPE) grown arsenic-doped HgCdTe were fabricated. The performances of the devices were investigated in this work. The profile of implanted pn junction on arsenic-doped HgCdTe was determined by a novel method. The results show that the junction depth is about 3.6~5.3 μm and the largest lateral size is about 130% of the designed value. In the experiment, HgCdTe long-wavelength photodiode arrays were fabricated by traditional and modified surface processing techniques. The modified process can improve the electrical properties of the devices significantly. The peak resistance and dynamic resistance at-05 V in the R-V curves of the devices by modified process is about 100 and 30 larger than those of the devices by traditional process, respectively. The reason of the improvement is assumed to be the suppression of surface leakage current.