This work reports results of a pilot study of planar HgCdTe-based avalanche photodiodes (APDs) realized by plasma-induced p-to-n type conversion on Hg-vacancy-doped HgCdTe grown by molecular beam epitaxy. The prototype APDs were designed for optimum photodetector performance at 2 \(\upmu \textrm{m}\) , with a 2.2 \(\upmu \textrm{m}\) cutoff wavelength absorber region. From spectral responsivity measurements, the maximum zero-bias external quantum efficiency was \(\sim \) 73% at 80 K, without anti-reflection coating, achieving a maximum avalanche gain of 177 at 10 V reverse bias under monochromatic 2 \(\upmu \textrm{m}\) wavelength illumination. Although the highest measured avalanche gain is significantly higher than previously reported in HgCdTe APDs with 2.5 \(\upmu \textrm{m}\) cutoff wavelength, additional research efforts will be necessary to overcome the significant scatter in attainable avalanche gain values and the deleterious impact of high surface leakage current on device performance. These aspects highlight the critical roles of surface passivation technology and device architecture in high-performance state-of-the-art APD technologies.
