Angle-Selective Photodetection in Ge/Si Quantum Dot Photodiodes Enhanced by Microstructured Hole Arrays.

We report on the near-infrared (NIR) photoresponse of a micropatterned Ge/Si quantum dot (QD) pin photodiode at different angles of radiation incidence. The photon-trapping hole array was etched through the n+-type top contact layer to reach the buried QDs. The normal-incidence responsivity was observed to be resonantly increased at wavelengths of 1.4, 1.7, and 1.9 μ m by factors of 40, 33, and 30, respectively, compared with the reference detector without holes. As the incident angle θ increases, the resonance peaks are disappeared and at θ > 40 ∘ a new resonance with a 25 × enhancement arises at a wavelength of 1.8 μ m. Simulation of the near-field intensity, Poynting vector distribution and wave polarization showed that at small θ , the strong electric field is primarily localized under the air holes (1.4 μ m, TM mode) or between the holes (1.7 and 1.9 μ m, TE modes) inside the region occupied by QDs, resulting in the strong NIR photocurrent. At large θ , the dominant resonance detected at 1.8 μ m is the result of coupling between the TE and TM modes and formation of a mixed near-field state. [ABSTRACT FROM AUTHOR]