Surface passivation of random alloy AlGaAsSb avalanche photodiode

Abstract 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 Al2O3 via atomic layer deposition (ALD). The dark currents of the APDs with 400‐µm diameter (dry etched) at 90% breakdown voltage (0.9 Vbr) 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, Si3N4 passivated, and Al2O3 passivated devices, respectively. The dark current at a gain of 10 for the Al2O3 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, Si3N4 passivated, and Al2O3 passivated devices, respectively. Moreover, punch‐through capacitance of 8 pF in a spectral response of 450 to 850 nm was obtained. Thus, Al2O3 passivation can be the best solution for antimonide optoelectronic devices.