Demonstration of Zn-Diffused Planar Long-Wavelength Infrared Photodetector Based on Type-II Superlattice Grown by MBE

We report on a planar long-wavelength infrared photodetector based on InAs/InAs _1-x Sb _x type-II superlattice with zinc diffusion. The superlattice structures were grown by molecular beam epitaxy, followed by a post-growth Zinc diffusion process in a metal-organic chemical vapor deposition reactor. The planar photodetectors showed a peak responsivity of 2.18 A/W, under an applied bias of −20 mV, with a corresponding quantum efficiency of 44.5%, without any anti-reflection coating, and had a 100% cut-off wavelength of $8.5 \mu \text{m}$ at 77 K temperature. These photodetectors exhibit a specific peak detectivity of $3.0\times 10^{12}$ cm.Hz ^1/2 /W, with a dark current density of $1.5\times 10^{-5}$ A/cm ² and the differential-resistance-area product of $\sim 8.6\times 10^{-1} \Omega $ .cm ² , under an applied bias of −20 mV at 77 K. A comparative study between the planar and conventional mesa-isolated photodetectors was also carried out.