A Low Dark Current Mesa-Type InGaAs/InAlAs Avalanche Photodiode

A top-illuminated three-mesa-type InGaAs/InAlAs separate absorption, grading, charge, and multiplication avalanche photodiode with a mesa larger than P contact mesa to reduce surface electric field, which achieves simultaneously the low dark current of planar type device and fabrication-simplicity and reproducibility of the mesa type one, is demonstrated. A high responsivity of 0.77 A/W (M = 1, without AR) at
$1.55~\mu $
m and high multiplication gain of more than 100 is achieved, whereas the dark current at 0.9 Vb is as low as 6 nA at room temperature (with 55-
$\mu $
m active region diameter). The dark current of devices of this structure is analyzed and proved to be mainly composed of surface leakage current and is significantly reduced compared with typical mesa structure devices with the same active region size while the capacitance is similar to that of typical mesa structure devices.