Thin absorber AlInAsSb 2-μm SACM APDs with very low and tunable dark currents at room-temperature

AlxIn1−xAsySb1−y digital alloys on GaSb separate absorber charge multiplier avalanche photodiodes that absorb at 2-μm wavelengths have been grown with relatively thin absorber layers ranging from 50 to 400 nm. These devices exhibit extremely low room-temperature dark currents owing to the reduced narrow bandgap absorber material. Compared to previously demonstrated devices, they maintain low dark currents out to high multiplication gains. Specifically, the 100-nm absorber device exhibits a room-temperature dark current density of ∼ 35 mA/cm2 at a multiplication gain of 90, which is the lowest reported room-temperature dark current for a 2 μm absorbing III-V avalanche photodiode operating at elevated gains. As the absorber region was thinned, bulk sources of dark current were suppressed, placing an emphasis on future work to suppress surface leakage and multiplier dark currents. Adjustments to the p-type charge region were also shown to yield large dark current improvements by reducing the electric field in the narrow bandgap absorber region.