Design and Fabrication of High-Efficiency, Low-Power, and Low-Leakage Si-Avalanche Photodiodes for Low-Light Sensing.

Since the advent of impact ionization and its application in avalanche photodiodes (APD), numerous application goals have contributed to steady improvements over several decades. The characteristic high operating voltages and the need for thick absorber layers (π-layers) in the Si-APDs pose complicated design and operational challenges in complementary metal oxide semiconductor integration of APDs. In this work, we have designed a sub-10 V operable Si-APD and epitaxially grown the stack on a semiconductor-on-insulator substrate with a submicron thin π-layer, and we fabricated the devices with integrated photon-trapping microholes (PTMH) to enhance photon absorption. The fabricated APDs show a substantially low prebreakdown leakage current density of ∼50 nA/mm2. The devices exhibit a consistent ∼8.0 V breakdown voltage with a multiplication gain of 296.2 under 850 nm illumination wavelength. We report a ∼5× increase in the EQE at 850 nm by introducing the PTMH into the device. The enhancement in the EQE is evenly distributed across the entire wavelength range (640-1100 nm). The EQE of the devices without PTMH (flat devices) undergo a notable oscillation caused by the resonance at specific wavelengths and show a strong dependency on the angle of incidence. This characteristic dependency is significantly circumvented by introducing the PTMH into the APD. The devices exhibit a significantly low off-state power consumption of 0.41 µW/mm2 and stand fairly well against the state-of-the-art literature. Such high efficiency, low leakage, low breakdown voltage, and extremely low-power Si-APD can be easily incorporated into the existing CMOS foundry line and enable on-chip, high-speed, and low-photon count detection on a large scale.