A passivation study for AlInAsSb avalanche photodiodes

Avalanche photodiodes (APDs) are vital for a wide range of commercial, military, and research applications. Recently, the AlxIn1–xAsySb1–y digital alloy system has emerged as a promising material for next-generation APDs, offering a broadly tunable bandgap, high avalanche gain, and low excess noise. However, surface oxidation and defect formation on the etched Al0.7InAsSb sidewalls of mesa-structure devices can significantly increase device dark currents, degrade the signal-to-noise ratio, and limit device reliability. Effective surface passivation is thus essential for suppressing dark current and enhancing device performance. In this study, we systematically compare the impact of different passivation techniques, including SU-8 polymer, atomic layer deposition (ALD)-HfO2, and ALD-Al2O3, deposited at various temperatures, on the performance of Al0.7InAsSb p–i–n APDs grown on InP substrates. Our results demonstrate that ALD-Al2O3 passivation at 150 °C achieves the most substantial reduction in dark current, increased breakdown voltage, and better thermal stability during heat exposure. This work provides valuable insights into developing high-performance, low-noise APDs suitable for demanding and commercially relevant optoelectronic applications.