Fleming F, Yi X, Mirza MMA, Jin X, Kirdoda J, Dumas DCS, Saalbach L, Modak M, Muir DAS, Smith C, Coughlan C, Tian Q, Millar RW, David JPR, Paul DJ, Buller GS. Surface-normal illuminated pseudo-planar Ge-on-Si avalanche photodiodes with high gain and low noise. Optics Express Vol. 32, Issue 11, pp. 19449-19457 (2024). DOI: 10.1364/OE.521417
Germanium-on-Silicon (Ge-on-Si) avalanche photodiodes (APDs) are of considerable interest as low intensity light detectors for emerging applications. The Ge absorption layer detects light at wavelengths up to ≈ 1600 nm with the Si acting as an avalanche medium, providing high gain with low excess avalanche noise. Such APDs are typically used in waveguide configurations as growing a sufficiently thick Ge absorbing layer is challenging. Here, we report on a new vertically illuminated pseudo-planar Ge-on-Si APD design utilizing a 2 µm thick Ge absorber and a 1.4 µm thick Si multiplication region. At a wavelength of 1550 nm, 50 µm diameter devices show a responsivity of 0.41 A/W at unity gain, a maximum avalanche gain of 101 and an excess noise factor of 3.1 at a gain of 20. This excess noise factor represents a record low noise for all configurations of Ge-on-Si APDs. These APDs can be inexpensively manufactured and have potential integration in silicon photonic platforms allowing use in a variety of applications requiring high-sensitivity detectors at wavelengths around 1550 nm.
