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 25x25 mu m(2) exhibit dark current densities of 10 nA/cm(2) at 295 K and responsivities of 0.62 A/W at 1550 nm.