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

We report Al0.3InAsSb/Al0.7InAsSb digital alloy n-barrier-n (nBn) photodetectors that operate in the 2-μm wavelength window. The AlxIn1-xAsySb1-y digital alloy material system exhibits near-zero valence-band offset, which is beneficial for nBn photodetectors. At 300 K these Al0.3InAsSb/Al0.7InAsSb 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.