Surface passivation of random alloy AlGaAsSb avalanche photodiode

AlGaAsSb attracts significant interest for near‐infrared avalanche photodiodes (APD). The authors report a two‐order reduction in the dark current and a six‐time enhancement of gain in random alloy (RA) AlGaAsSb APD that is surface passivated by conformal coating of Al 2 O 3 via atomic layer deposition (ALD). The dark currents of the APDs with 400‐µm diameter (dry etched) at 90% breakdown voltage (0.9 V br ) are (5.5 ± 0.5) × 10 −5 A, (2.1 ± 0.4) × 10 −5 A, and (6.2 ± 0.8) × 10 −7 A for non‐passivated, Si 3 N 4 passivated, and Al 2 O 3 passivated devices, respectively. The dark current at a gain of 10 for the Al 2 O 3 passivated device is 1 × 10 −8 A which is comparable to the reported value for 100‐µm diameter mesa diodes passivated by SU‐8. Maximum gain values of 6, 12, and 35 were obtained for non‐passivated, Si 3 N 4 passivated, and Al 2 O 3 passivated devices, respectively. Moreover, punch‐through capacitance of 8 pF in a spectral response of 450 to 850 nm was obtained. Thus, Al 2 O 3 passivation can be the best solution for antimonide optoelectronic devices.