High-speed waveguide integrated silicon photodetector on a SiN-SOI platform for short reach datacom

Abstract

We present waveguide integrated high-speed Si photodetector integrated with silicon nitride (SiN) waveguide on SOI platform for short reach data communication in 850 nm wavelength band. We demonstrate a waveguide couple Si pin photodetector responsivity of 0.44 A/W at 25 V bias. The frequency response of the photodetector is evaluated by coupling of a femtosecond laser source through SiN grating coupler of the integrated photodetector. We estimate a 3dB bandwidth of 14 GHz at 20 V bias, highest reported bandwidth for a waveguide integrated Si photodetector. We also present detailed optoelectronic DC and AC characterisation of the fabricated devices. The demonstrated integrated photodetector could enable an integrated solution for scaling of short reach data communication and connectivity.Ever increasing data traffic drives the need for scalable, high speed, and energy efficient connectivity in the datacenters [1-3]. Optical connectivity offers an excellent solution to data connectivity bottleneck in datacenters. Widely used 850 nm VCSEL based Multimode fiber (MMF) technology is reaching maximum capacity, however, proposal to extend the MMF toward Wavelength Division Multiplexing (WDM) would scale up the capacity to 400 Gbps. In view of that, IEEE proposed 400 Gbps roadmap [4] for short reach rack-to-rack communication by 2020. Adapting WDM would require integration of wavelength multiplexers and demultiplexers, light sources and detectors in a single module. Integrating all the functional elements as a single photonic integrated circuit would enable a compact, costeffective, and scalable platform. Fig. 1. Schematics of the proposed waveguide coupled Si photodetector. (a) SiN waveguide on SiO2, (b) Tapered Si waveguide vertically coupled to SiN, and (c) Si pin photodetector with SiN waveguide.It is essential that the circuit should be able to guide light with low-loss and is compact with the integration of light sources and detectors. Silicon (Si) photonics has demonstrated such a versatile platform in 1310 nm and 1550 nm wavelength band [5][6][7]. A similar strategy could enable a photonic circuit platform in 850 nm band as well. Recently, efforts are made to integrate III-V light sources and III-V/Graphene photodetectors on Silicon Nitride (SiN) waveguide platform [7,8]. However, such hybrid integration requires complex assembly and post-processing technology, also the fabrication is not compatible with preferred Si process technology. It is desirable to reduce such non-standard integration. In this regards, Si is an excellent photodetector in the 850 nm band with higher responsivity than III-V photodetector. However, longer absorption length, RC time, and transit time in Si considerably limit bandwidth [9][10][11]. The bandwidth limitation of Si photodetector is significantly improved by realizing lateral pin photodetector in a guided wave configuration, particularly in a Silicon-on-Insulator (SOI) platform [12]. The thin Si in SOI has smaller depletion capacitance, which enhances the RC time limited bandwidth....

Coupling of Photonic Waveguides to Integrated Detectors Using 3D Inverse Tapering

“…We note, that the measured responsivities are comparable with the state-of-the-art R's in waveguide-integrated photodetectors, which are typically of the order of 0.3 A/W [6], [7], [5]. Here, the lower values of R can be explained by the fact that the absorbance value of the realized devices is mostly limited by the thickness of the epitaxial layer, which is 3 µm in our devices.…”

“…We acknowledge financial support from the Autonomous Province of Trento, under the initiative "Quantum at Trento -Q@TN", projects Q-PIXPAD and CoSiQuP. [6] other (polysi) 0.15 0.8 [7] other (SOI) 0.22 0.44 [8] other (SOI) 0.22 0.32 [9] other (SOI) 0.25 0.74 [10] other (transf. SOI) 0.22 0.19 [11] other (SOI,λ =685nm) 0.25 0.83…”

Promoting the Performance of 2D Material Photodetectors by Dielectric Engineering

“…It is evident that the overall performances of the SiO 2 /STO (300 nm) -WSe 2 photodetector have overmatched most of the state-of-theart 2DM-based photodetectors, which have been improved by a wealth of strategies such as waveguide integration, [7,10] surface oxidation, [15] surface modification, [29] dual-channel configuration [30] as well as dual-gating configuration. [22,31] In addition, this device also outperforms the state-of-the-art commercial photodetectors (Section S6, Supporting Information) as well as photodetectors based on conventional semiconductors such as silicon, [32] germanium, [33] and GaAs. [34] Benefiting from the excellent photosensitivity, the SiO 2 /STO (300 nm) -WSe 2 photodetector demonstrates remarkable capability to capture weak light signal (Section S7, Supporting Information).…”

Integrated avalanche photodetectors for visible light

“…The majority of recent research in this area has been geared towards applications in optical communications networks, focusing on operation at infrared telecommunications wavelengths. These devices have been developed on a variety of material platforms, including III-V semiconductors [4], germanium (Ge) [5][6][7], and Si [8][9][10][11].…”

“…Despite the ubiquity and high performance of free-space APDs for visible light detection, integrated versions present a host of technical challenges. To date, the shortest operating wavelength among integrated APDs is 850 nm, as demonstrated in devices developed for shortreach data communications [9,11]. To the best of our knowledge, there are no reports of visible-light integrated APDs in the literature.…”