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.