Graphene field-effect transistors have been intensively studied.However,in order to fabricate devices with more complicated structures,such as the integration with waveguide and other two-dimensional materials,we need to transfer the exfoliated graphene samples to a target position.Due to the small area of exfoliated graphene and its random distribution,the transfer method requires rather high precision.In this paper,we systematically study a method to selectively transfer mechanically exfoliated graphene samples to a target position with a precision of sub-micrometer.To characterize the doping level of this method,we transfer graphene flakes to pre-patterned metal electrodes,forming graphene field-effect transistors.The hole doping of graphene is calculated to be 2.16×10^12cm^-2.In addition,we fabricate a waveguide-integrated multilayer graphene photodetector to demonstrate the viability and accuracy of this method.A photocurrent as high as 0.4 μA is obtained,corresponding to a photoresponsivity of 0.48 mA/W.The device performs uniformly in nine illumination cycles.
We present the design of a diffractive grating structure and get the optimal parameters which can achieve more than 75%coupling efficiency（CE） between single-mode fiber and silicon-on-insulator（SOI） waveguide through 2D finite-different time-domain（FDTD） simulation.The proposed architecture has a uniform structure with no bottom reflection element or silicon overlay.The structure,including grating couplers,adiabatic tapers and interconnection waveguides can be fabricated on the SOI waveguide with only a single electron-beam lithography（ICP） step,which is CMOS-compatible.A relatively high coupling efficiency of 47.2%was obtained at a wavelength of 1562 nm.
Rongrui LiuYubing WangDongdong YinHan YeXiaohong YangQin Han
Recently, graphene-based photodetectors have been rapidly developed. However, their photoresponsivities are generally low due to the weak optical absorption strength of graphene. In this paper, we fabricate photoconductive multi-layer graphene（MLG） photodetectors on etched silicon-on-insulator substrates. A photoresponsivity exceeding 200 A·W-1is obtained, which enables most optoelectronic application. In addition, according to the analyses of the high photoresponsivity and long photoresponse time, we conclude that the working mechanism of the device is photoconductive effect. The process of photons conversion into conducting electrons is also described in detail. Finally, according to the distinct difference between the photoresponses at 1550 nm and 808 nm, we estimate that the position of the trapping energy is somewhere between 0.4 e V and 0.76 e V, higher than the Fermi energy of MLG. Our work paves a new way for fabricating the graphene photoconductive photodetectors.
Graphene is an alternative material for photodetectors owing to its unique properties.These include its uniform absorption of light from ultraviolet to infrared and its ultrahigh mobility for both electrons and holes.Unfortunately,due to the low absorption of light,the photoresponsivity of graphene-based photodetectors is usually low,only a few milliamps per watt.In this letter,we fabricate a waveguide-integrated graphene photodetector.A photoresponsivity exceeding0.11 A·W （-1） is obtained which enables most optoelectronic applications.The dominating mechanism of photoresponse is investigated and is attributed to the photo-induced bolometric effect.Theoretical calculation shows that the bolometric photoresponsivity is 4.6 A·W （-1）.The absorption coefficient of the device is estimated to be 0.27 dB·μm （-1）.
This paper presents a high-responsivity and high-speed InGaAs/InP PIN photodetector integrated onto the silicon waveguide substrate utilizing the divinyltetramethyldisiloxane-benzocyclobutene （DVS-BCB） adhesive bonding method. A grating coupler is adopted to couple light from the fiber to the silicon waveguide. Light in the silicon photonic waveguide is evanescently coupled into the photodetector. The integrated photodetector structure is first simulated using the FDTD （finite difference time domain） solutions software and the simulation results show a detection efficiency of 95%. According to the simulation result, the integrated photodetector is fabricated. The measured responsivity of the fabricated integrated photodetector with a detection length of 30μm is 0.89 A/W excluding the coupling loss between the fiber and the grating coupler and the silicon propagation loss at the wave-length of 1550 nm with a reverse bias voltage of 3 V. Measured 3-dB bandwidth is 27 GHz using the Lightwave Component Analyzer （LCA）. The eye diagram signal test results indicate that the photodetector can operate at a high speed of 40 Gbit/s. The integrated photodetector is of great significance in the silicon-based optoelectronic integrated chip which can be applied to the optical communication and the super node data transmission chip of the high-performance computer.
