Al0.3InAsSb/Al0.7InAsSb Digital Alloy nBn Photodetectors

We report Al _0.3 InAsSb/Al _0.7 InAsSb digital alloy n-barrier-n ( nBn ) photodetectors that operate in the 2-µm wavelength window. The Al _x In _1-x As _y Sb _1-y digital alloy material system exhibits near-zero valence-band offset, which is beneficial for nBn photodetectors. At 300 K these Al _0.3 InAsSb/Al _0.7 InAsSb nBn photodetectors have achieved specific detectivities of 1.7 × 10 ¹⁰ and 3.0 × 10 ¹⁰ Jones under 2-µm and 1.8-µm illumination, respectively. The dark current density at −0.5 V bias decreases from 3.1 × 10 ⁻³ A/cm ² at 300 K to 1.6 × 10 ⁻¹⁰ A/cm ² at 120 K, where the dominant dark current component is tunneling. The area-dependence of key performance parameters show that for mesa diameter ≤ 250 µm, surface defects assume a dominant role in the total noise.