Mesa-isolated InGaAs photodetectors with low dark current

We demonstrate InGaAs photodiodes with an epitaxial heterostructure that allows simple mesa isolation of individual devices with low dark current and high responsivity. An undoped InAlAs barrier and passivation layer enables isolation of detectors without exposing the InGaAs active region, while simultaneously reducing electron diffusion current. Photodetectors with mesa sizes as small as 25×25 μm2 exhibit dark current densities of 10 nA/cm2 at 295 K and responsivities of 0.62 A/W at 1550 nm.