  The increasing concentration of greenhouse gases, notably CH4 and CO2, has
fueled global temperature increases, intensifying concerns regarding the
prevailing climate crisis. Effectively monitoring these gases demands a
detector spanning the extended short-wavelength infrared (~2.4 {\mu}m) range,
covering wavelengths of CH4 (1.65 {\mu}m) and CO2 (2.05 {\mu}m). The
state-of-the-art HgCdTe avalanche photodetectors (APDs) offer exceptional
performance metrics, including high gain (M) and low excess noise (F). However,
their widespread adoption is hindered by inherent challenges such as
manufacturability, reproducibility, and cost factors. Moreover, their reliance
on cryogenic cooling adds to the cost, size, weight, and power of the system.
We have demonstrated a linear mode APD combining an InGaAs/GaAsSb type-II
superlattice absorber and an AlGaAsSb multiplier lattice matched to InP
substrates. This APD has demonstrated a room temperature M of 178, a maximum
measurable external quantum efficiency of 3560 % at 2 {\mu}m, an extremely low
excess noise (F < 2 at M < 20), and a small temperature coefficient of
breakdown (7.58 mV/K {\mu}m). Such a high performance APD with manufacturable
semiconductor materials could lead to a rapid transition to a commercial III-V
foundry, holding the promise of revolutionizing high-sensitivity receivers for
greenhouse gas monitoring.
