Jun Deng

Growth front nucleation of rubrene thin films for high mobility organic transistors

We demonstrate a mode of thin film growth in which amorphous islands crystallize into highly oriented platelets. A cascade of crystallization is observed, in which platelets growing outward from a central nucleation point impinge on neighboring amorphous islands and provide a seed for further nucleation. Through control of growth parameters, it is possible to produce high quality thin films which are well suited to the formation of organic transistors. We demonstrate this through the fabrication of rubrene thin film transistors with high carrier mobility.

GaN nanorod light emitting diodes with suspended graphene transparent electrodes grown by rapid chemical vapor deposition

Ordered and dense GaN light emitting nanorods are studied with polycrystalline graphene grown by rapid chemical vapor deposition as suspended transparent electrodes. As the substitute of indium tin oxide, the graphene avoids complex processing to fill up the gaps between nanorods and subsequent surface flattening and offers high conductivity to improve the carrier injection. The as-fabricated devices have 32% improvement in light output power compared to conventional planar GaN-graphene diodes. The suspended graphene remains electrically stable up to 300u2009°C in air. The graphene can be obtained at low cost and high efficiency, indicating its high potential in future applications.

Wide operation range in-phase coherently coupled vertical cavity surface emitting laser array based on proton implantation.

In-phase coherently coupled vertical cavity surface emitting laser (VCSEL) hexagonal arrays were fabricated using proton implantation. The near-field profiles, far-field profiles, and emission spectra under different injection currents were tested and analyzed. The arrays can maintain in-phase single mode in a considerably wide current range from 10 mA (I(th)) to 35 mA (3.5×I(th)), exhibiting excellent beam quality. The far-field divergence angle of the in-phase coupled array is 2.5 degrees. Approximately 29% of total power is localized in the central lobe. Compared with square structure arrays, hexagonal arrays can maintain a more stable in-phase mode because of stronger coupling among the elements. The maximum output power of 4.9 mW was obtained under pulse wave condition. The simulation of far-field was carried out to match the in-phase operation test results. The performance enhancement of the array is attainable if the condition of heat dissipation is better. The process procedure of proton implantation is relatively simple and of low cost. It can be used as an alternative to coherently coupled array implementations.

High responsivity sensing of unfocused laser and white light using graphene photodetectors grown by chemical vapor deposition

Graphene photodetectors grown by chemical vapor deposition are fabricated for unfocused laser and white light sensing. The unfocused light enlarges the illuminated graphene area and mimics the real-life sensing conditions, yielding a responsivity of 104 mA/W at room temperature without enhancing absorbance by waveguide and plasmonics. The devices are based on positive photoconductivity from the electron-hole photocarrier pairs and the bolometric-effect-induced negative photoconductivity. The buried off-center local gate induces a net internal potential in the graphene. The relative strength of the two photoconductivities depends on the gate voltage. The technology is scalable, which is a step ahead toward real applications.

Electrochemical Bubbling Transfer of Graphene Using a Polymer Support with Encapsulated Air Gap as Permeation Stopping Layer

Electrochemical bubbling transfer of graphene is a technique with high industrial potential due to its scalability, time- and cost-effectiveness, and ecofriendliness. However, the graphene is often damaged due to the turbulence and the trapped bubbles formed by the direct H2O and H+ permeation through the supporting polymer. We invent a graphene mechanical support of polyethylene terephthalate foil/plastic frame/polymethyl methacrylate sandwich, with an encapsulated air gap as the permeation stopping layer. The graphene damage is drastically reduced, as confirmed by the morphology and structural and electrical characterization, ultimately improving the controllability/reproducibility of the bubbling transfer of graphene and other two-dimensional materials.

Large-Scale Proton-Implant-Defined VCSEL Arrays With Narrow Beamwidth

In-phase coherently coupled proton-implant-defined vertical cavity surface emitting laser (VCSEL) arrays face difficulties in current spreading, resulting in small array scale, low output power, and broad beamwidth. Although patterned metal grids can improve the current spreading, the undesirable out-of-phase mode tends to be dominant in the array. In this letter, by means of engineering the implantation and array parameters, in-phase mode is obtained in large-scale proton-implant-defined arrays with metal grids. Experimental results show that these arrays are operating in in-phase mode with a nominal interelement spacing of 8 <inline-formula> <tex-math notation=LaTeX>

Mechanism of Electrochemical Delamination of Two-Dimensional Materials from Their Native Substrates by Bubbling

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Transfer-free, lithography-free, and micrometer-precision patterning of CVD graphene on SiO2 toward all-carbon electronics

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Simulation of Far-Field Properties of Coherent Vertical Cavity Surface Emitting Laser Array*

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Phase tuning in two-dimensional coherently coupled vertical-cavity surface-emitting laser array

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