Long-wavelength (8-14μm) infrared detection ability using third-generation infrared focal plane array (FPAs) is a desideratum for aerography, military and communication. These optical bands contain tremendous information about CO<sub>2</sub> levels, atmospheric quality and biological activity. HgCdTe infrared photodetectors are able to reach high degree of performance even to be background limited. However, the material growth process, doping techniques and capability of defect control become increasingly difficult for the shrinking bandgap. Besides, the dark current characteristic and associated noise behavior are very sensitive to the detector fabrication processes. Thereby, the growth of p-type epitaxial layer is a fundamental and significant subject for long-wavelength HgCdTe infrared photodetector.