Yichen Shuai

An aqueous solution-based doping strategy for large-scale synthesis of Sb-doped ZnO nanowires

An aqueous solution-based doping strategy was developed for controlled doping impurity atoms into a ZnO nanowire (NW) lattice. Through this approach, antimony-doped ZnO NWs were successfully synthesized in an aqueous solution containing zinc nitrate and hexamethylenetetramine with antimony acetate as the dopant source. By introducing glycolate ions into the solution, a soluble antimony precursor (antimony glycolate) was formed and a good NW morphology with a controlled antimony doping concentration was successfully achieved. A doping concentration study suggested an antimony glycolate absorption doping mechanism. By fabricating and characterizing NW-based field effect transistors (FETs), stable p-type conductivity was observed. A field effect mobility of 1.2 cm(2) V(-1) s(-1) and a carrier concentration of 6 × 10(17) cm(-3) were achieved. Electrostatic force microscopy (EFM) characterization on doped and undoped ZnO NWs further illustrated the shift of the metal-semiconductor barrier due to Sb doping. This work provided an effective large-scale synthesis strategy for doping ZnO NWs in aqueous solution.

Approaching total absorption at near infrared in a large area monolayer graphene by critical coupling

We demonstrate experimentally close to total absorption in monolayer graphene based on critical coupling with guided resonances in transfer printed photonic crystal Fano resonance filters at near infrared. Measured peak absorptions of 35% and 85% were obtained from cavity coupled monolayer graphene for the structures without and with back reflectors, respectively. These measured values agree very well with the theoretical values predicted with the coupled mode theory based critical coupling design. Such strong light-matter interactions can lead to extremely compact and high performance photonic devices based on large area monolayer graphene and other two–dimensional materials.

Coupled double-layer Fano resonance photonic crystal filters with lattice-displacement

We present here ultra-compact high-Q Fano resonance filters with displaced lattices between two coupled photonic crystal slabs, fabricated with crystalline silicon nanomembrane transfer printing and aligned e-beam lithography techniques. Theoretically, with the control of lattice displacement between two coupled photonic crystal slabs layers, optical filter Q factors can approach 211 000 000 for the design considered here. Experimentally, Q factors up to 80 000 have been demonstrated for a filter design with target Q factor of 130 000.

Double-layer Fano resonance photonic crystal filters.

We report ultra-compact surface-normal high-Q optical filters based on single- and double-layer stacked Fano resonance photonic crystal slabs on both Si and quartz substrates. A single layer photonic crystal filter was designed and a Q factor of 1,737 was obtained with 23 dB extinction ratio. With stacked double-layer photonic crystal configuration, the optical filter Q can increase to over 10,000,000 in design. Double-layer filters with quality factor of 9,734 and extinction ratio of 8 dB were experimentally demonstrated, for a filter design with target Q of 22,000.

Fano-Resonance Photonic Crystal Membrane Reflectors at Mid- and Far-Infrared

We report here single-layer ultracompact Fano-resonance photonic crystal membrane reflectors (MRs) at mid-infrared (IR) and far-IR (FIR) bands, based on single layer crystalline Si membranes. High-performance reflectors were designed for surface-normal incidence illumination with center operation wavelengths up to the 75-μm FIR spectral band. Large-area patterned MRs were also fabricated and transferred onto glass substrates based on membrane transfer processes. Close to 100% reflection was obtained at the ~ 76-μm spectral band, with a single-layer Si membrane thickness of 18 μm. Such Fano-resonance-based membranes reflectors offer great opportunities for high-performance ultracompact dielectric reflectors at IR and THz regions.

High-order grating coupler for high-efficiency vertical to in-plane coupling

We present here the design of a robust broadband high efficiency surface-normal vertical to in-plane optical coupler using fourth-order gratings. The fourth-order gratings can be designed such that the zero-order diffraction is suppressed while the diffraction efficiencies of the higher orders are enhanced for the in-plane coupling. We numerically demonstrated the surface normal incidence light coupling efficiency of 88.5% at 1,535 nm with a 3 dB bandwidth of 42 nm and 1dB bandwidth of 28 nm. Large fabrication tolerance of the fourth-order grating is also assessed.

Stacked double-layer nanomembrane Fano modulators

We report a novel bi-layer photonic crystal slab (PCS) Fano modulator via a coupled double-layer Si nanomembrane (SiNM) capacitor like structure. Surface normal incident light intensity modulation near 1500nm was achieved by carrier accumulation induced resonance spectral shifting. Device performance simulation suggests the opportunity for high speed modulation exceeding GHz with 20μm × 20μm device size.

High-performance photonic crystal membrane reflectors by magnetically guided metal-assisted chemical etching

Based on Fano resonance principles in photonic crystals, high performance broadband reflectors can be realized with 100% reflection. Applying an innovative magnetic field guided metal-assisted chemical etching (MacEtch) process, we report here high performance membrane reflectors on SOI with controlled sidewall etching and high reflection around 1550 nm. This work represents the first demonstration of magnetically guided MacEtch (h-MacEtch) of periodic arrays of discrete nanoholes of sub-micron dimensions. Such an innovative process can lead to facile formation of large area 2D and 3D nanoscale-structures, for high performance photonic crystal membrane reflectors, filters, and metamaterials.

Spectral selective absorption enhancement from stacked ultra-thin InGaAs/Si Fano resonance membranes

We report here modified absorption property of InGaAs nano-membrane on a Fano filter made of patterned single crystalline silicon nano-membrane transferred onto glass substrate. Placement of an ultra-thin InGaAs film on Si Fano resonant membrane enhances the absorption with simulated enhancement factor ~35 and measured enhancement factor of ~26. Leaky modes in the photonic crystal (PC) consist of high field standing waves that can be coupled to the out of plane radiation mode provided by lattice matching of the PC. We will present simulation, device fabrication and experimental characterization of stacked ultra-thin InGaAs/Si Fano resonance membrane in the IR regime.

Fano resonance membrane reflectors from mid-infrared to far-infrared

The authors report here single layer ultra-compact Si MRs at mid-infrared and far-infrared bands, based on suspended air-clad structure. High performance reflectors were designed for surface- normal incidence with center operation wavelengths of 1.5 μm, ~ 8 μm, and 75 μm, respectively. Large area patterned membrane reflectors were also fabricated and transferred onto glass substrates based on PDMS stamp assisted membrane transfer process. Close to 100% reflection was obtained at ~76 μm, with a single layer Si membrane thickness of 18 μm.