Resonant-cavity-enhanced Ge/Ge1− xSnx metal-semiconductor-metal photodetector for 2 μm-band applications

In this work, we propose high-speed and efficient resonant-cavity-enhanced (RCE) Ge/Ge1−x Sn x metal-semiconductor-metal (MSM) photodetectors (PDs) integrated with p-Si interlayer that operate in the 2 um band. Additionally, the p-Si interlayer is employed in the proposed device structure to increase the Schottky barrier height and hence decrease the dark current. With the introduction of a bottom mirror, the Si/SiO2 Distributed-Bragg reflector (DBR) significantly improves the poor absorption of the conventional GeSn MSM PD. Furthermore, in the optical cavity formed by the bottom mirror and SiO2 top mirror, we incorporate an ultrathin i- Ge1−x Sn x active layer. As a result, the proposed RCE PD exhibits exceptionally strong optical fields within the optical cavity as a result of the light resonance. Moreover, this work presents techniques to balance the trade-off between responsivity and the 3 dB bandwidth. Hence, the proposed RCE MSM PD with Ge1−x Sn x (x = 9%) thickness of 25 nm demonstrates outstanding performance at λ = 2 μm, attaining a responsivity of 0.76 A W−1 and a 3 dB bandwidth of 58.1 GHz, all achieved with only two pairs of DBR. These values are significantly higher than the majority of the theoretical values that are currently available. This efficient and fast PD opens up new possibilities for silicon-integrated photonic circuits and their potential applications at 2 um bands.