COMMUNICATIONIn this paper, we present a highly broadband (from visible to infrared) photodetector based on chemical vapor deposition (CVD) graphene-silicon heterostructure, together to be operated in photoconductor mode. This device shows very high responsivity (>10 4 A W −1 ) at wavelength of 632 nm, where light absorption relies on silicon. More importantly, even in the infrared region (1550 nm), where light absorption only depends on the graphene, the responsivity of our detector can be as high as 0.23 A W −1 , which is much higher those by pure monolayer graphene-based devices without optically assisted structure in this spectral region. [ 13,15,24 ] The signifi cant response is mainly due to the fact that the built-in fi eld in heterostructure can effectively prolong the ultrashort lifetime of photon-induced carriers. Besides, we also fi nd three dynamic processes in the transient response: photo-induced carriers sweeping into graphene by the built-in fi eld, electrons in the depletion region diffusion back to graphene, and photo-induced carriers in the bulk silicon diffusion to graphene. Due to the fi rst mechanism, the response time of our detector is less than 3 µs, which has not been reported among graphene photoconductor/ phototransistors. [ 1 ] The structure of graphene-silicon heterostructural photodetector is schematically shown in Figure 1 a. The start wafer we employed is a lightly doped p-type silicon wafer (>100 Ω). A thin layer of SiO 2 is grown on silicon and patterned a window on top. Then, the CVD graphene (the Raman spectra is shown in Figure S1, Supporting Information) is transferred, and both electrodes are deposited on graphene. The SiO 2 layer can avoid the overlap between the electrode and silicon. A Schottky junction is thus formed at the interface between graphene and silicon. The Fermi level differences are measured by Kelvin probe force microscopy (KPFM) in the dark. As shown in Figure 1 b, the surface potential differences (approximately similar to the work function misalignment for clean samples) between graphene and silicon, and between graphene and gold are about 0.08 and 0.16 eV, respectively. Under ambient conditions, the work function of gold is around 4.8 to 4.9 eV. [ 25,26 ] By taking the intrinsic work function of graphene (≈4.56 eV) [30][31][32] into consideration, an energy band diagram is depicted in Figure 1 c. The Fermi energy of graphene should be around 0.16 to 0.26 eV. A built-in fi eld forms at the surface, which directs from silicon to graphene. The graphene not only functions as the charge transport channel, but also works as the light absorber for the light with photon energy lower than the Fermi energy.In the visible light experiment, the photodetector is characterized by the laser at wavelength of 625 nm. Optical attenuators are introduced to change the input power. DOI: 10.1002/adom.201500127Graphene is thought to be an ideal material for novel photodetectors due to its unique properties. [1][2][3] For example, its zero bandgap affords the benefi t of ultr...

We demonstrated strong optical absorption in a graphene integrated silicon slot waveguide. Due to the increase in light intensity and decrease of optical mode confinement in the silicon slot, the graphene experienced an increased interaction to the in-plane light. A waveguide absorption of 0.935 dB μm(-1) was measured at 1.55 μm wavelengths. Based on the graphene-on-silicon slot waveguide, a compact and high-responsivity photodetector was demonstrated. Benefited from the lack of efficient electron cooling in the suspended graphene and the intensity enhancement effect in the nano slot, a maximum responsivity of 0.273 A W(-1) was achieved in the telecommunication band.

We demonstrated a graphene photodetector integrated on silicon nitride waveguide. The photodetector worked in the photoconductor mode. The detection mechanisms of the device were based on photo-thermoelectric effect and bolometric effect. The waveguide absorption (0.025 dB/μm) with a chemical vapor deposition grown monolayer graphene on top was studied experimentally. The measurement agreed well with the simulation result. The Fermi level of the top layer graphene in the photodetector was analyzed by using the field-effect transport measurement. A maximum internal responsivity of 126 mA/W with dynamic response of 1 K Hz was achieved in the telecommunication band. The unique combination of graphene and silicon nitride integrated circuit can potentially lead to unprecedented nonlinear and optoelectronic applications.

Silicon photonic devices are being used in the photonics industry over the past three decades has helped in realizing large-scale photonic integrated circuits. Silicon nitride (Si3N4) is another CMOScompatible platform that provides several advantages such as low loss, high optical power tolerance, and broad spectral operation band from visible to infrared wavelengths. Recently, the combination of Si3N4waveguide technology with silicon photonics and III-V materials has opened up new areas in the field of on-chip applications. Researchers in this field are primarily focusing on its applications such as on-chip gas sensing, nonlinear optical signal processing, and label-free biosensors based on photonic integrated circuits. In this review paper, we discuss Si3N4material-based platforms for variety of applications with devices ranging from passive to active and hybrid photonic devices.

Graphene-on-silcon nitride (Si 3 N 4 ) microring resonators were theoretically optimized and experimentally demonstrated to enhance their absorption. The original absorption of 25 dB/mm in a graphene-on-Si 3 N 4 straight waveguide was significantly enhanced through the resonator structure, offering a quality factor from ∼28 200 to ∼3800 depending on the graphene length in the cavity. The result agrees well with theoretical calculations. The characterization study in this letter is useful in developing graphene-on-Si 3 N 4 microring resonator structure for high-performance optical modulators and photodetectors.