Enhanced Performance of Extended Wavelength InxGa1–xAs Focal Plane Arrays via Compositional Overshooting of InxAl1–xAs Buffer Layer

Performances of In0.75 Ga0.25 As focal plane arrays (FPAs) with an extended cutoff wavelength of $2.2~\mu $ m are remarkably improved by largely increasing the overshooting composition of the linearly-grading Inx Al ${}_{\text {1-x}}$ As buffer layer. Zinc-diffused planar $640\times 488$ FPAs with a pixel pitch of $23~\mu $ m are fabricated on both the regular and the large overshooting epi-wafers with x=0.77 and x=0.85 for the end compositions of the linearly-grading Inx Al ${}_{\text {1-x}}$ As, respectively. An order of magnitude lower dark current density of $1.1 \times 10 ^{-10}$ A/cm2 is achieved at 150 K for the large overshooting FPAs when comparing with $2.1\times 10 ^{-9}$ A/cm2 for the regular FPAs. Suppressed dark signal and dark noise voltages are observed simultaneously over the measured whole integration time range. Moreover, the measured non-uniformity of the light response signal voltage drastically dropped from 16.4% to 2.9% while the peak detectivity substantially jumped from $7.1 \times 10 ^{12}$ to $1.8 \times 10 ^{13}$ cmHz ${}^{1/2}$ W−1. A signal to noise ratio enhanced laboratory imaging demonstration is also provided. These results suggest the large overshooting epitaxial technology can serve as a highly viable route for the lattice-mismatched Inx Ga ${}_{\text {1-x}}$ As FPAs towards further performance enhancement.