arXiv subjects

Xing

Publications and source records attributed to Xing.

24 records · Page 2Linked to original sources

arXiv2013

Graphene Nanoribbon Field-Effect Transistors on Wafer-Scale Epitaxial Graphene on SiC substrates

We report the realization of top-gated graphene nanoribbon field effect transistors (GNRFETs) of ~10 nm width on large-area epitaxial graphene exhibiting the opening of a band gap of ~0.14 eV. Contrary to prior observations of disordered transport and severe edge-roughness effects of GNRs, the experimental results presented here clearly show that the transport mechanism in carefully fabricated GNRFETs is conventional band-transport at room temperature, and inter-band tunneling at low temperature. The entire space of temperature, size, and geometry dependent transport properties and electrostatics of the GNRFETs are explained by a conventional thermionic emission and tunneling current model. Our combined experimental and modeling work proves that carefully fabricated narrow GNRs behave as conventional semiconductors, and remain potential candidates for electronic switching devices.

cond-mat.mes-hall↗

arXiv2013

A Surface-Potential Based Compact Model for GaN HEMTs Directly Incorporating Polarization Charges

A method to incorporate polarization charges at heterojunctions in compact models for transistors is presented. By including the polarization sheet charge as a Dirac delta function, the Poisson equation is solved to yield a closed equation for the surface potential. A compact model for transistors based on the surface potential incorporating polarization charges describes the on-state as well as the off-state regimes of device operation. The new method of incorporating polarization charges in compact models helps make a direct connection to the material properties of the transistor. The current-voltage (I-V) curves generated by this model are in good agreement with the experimental data for GaN HEMTs.

cond-mat.mes-hall↗

arXiv2013

Comparative Study of Chemically Synthesized and Exfoliated Multilayer MoS2 Field-Effect Transistors

We report the realization of field-effect transistors (FETs) made with chemically synthesized multilayer 2D crystal semiconductor MoS2. Electrical properties such as the FET mobility, subthreshold swing, on/off ratio, and contact resistance of chemically synthesized (s-) MoS2 are indistinguishable from that of mechanically exfoliated (x-) MoS2, however flat-band voltages are different, possibly due to polar chemical residues originating in the transfer process. Electron diffraction studies and Raman spectroscopy show the structural similarity of s-MoS2 to x-MoS2. This initial report on the behavior and properties of s-MoS2 illustrates the feasibility of electronic devices using synthetic layered 2D crystal semiconductors.

cond-mat.mes-hall↗

arXiv2012

Transport Properties of Graphene Nanoribbon Transistors on Transport Properties of Graphene Nanoribbon Transistors on Chemical-Vapor-Deposition Grown Wafer-Scale Graphene

Graphene nanoribbon (GNR) field-effect transistors (FETs) with widths down to 12 nm have been fabricated by electron beam lithography using a wafer-scale chemical vapor deposition (CVD) process to form the graphene. The GNR FETs show drain-current modulation of approximately 10 at 300 K, increasing to nearly 106 at 4 K. The strong temperature dependence of the minimum current indicates the opening of a bandgap for CVD-grown GNR-FETs. The extracted bandgap is estimated to be around 0.1 eV by differential conductance methods. This work highlights the development of CVD-grown large-area graphene and demonstrates the opening of a bandgap in nanoribbon transistors.

cond-mat.mes-hall↗

arXiv2012

Transistors with Chemically Synthesized Layered Semiconductor WS2 Exhibiting 105 Room Temperature Modulation and Ambipolar Behavior

We report the realization of field-effect transistors (FETs) made with chemically- synthesized layered two dimensional (2D) crystal semiconductor WS2. The 2D Schottky-barrier FETs demonstrate ambipolar behavior and a high (~105x) on/off current ratio at room temperature with current saturation. The behavior is attributed to the presence of an energy bandgap in the 2D crystal material. The FETs show clear photo response to visible light. The promising electronic and optical characteristics of the devices combined with the layered 2D crystal flexibility make WS2 attractive for future electronic and optical devices.

cond-mat.mes-hall↗

arXiv2011

Unique prospects of graphene-based THz modulators

The modulation depth of 2-D electron gas (2DEG) based THz modulators using AlGaAs/GaAs heterostructures with metal gates is inherently limited to < 30%. The metal gate not only attenuates the THz signal (> 90%) but also severely degrades the modulation depth. The metal losses can be significantly reduced with an alternative material with tunable conductivity. Graphene presents a unique solution to this problem due to its symmetric band structure and extraordinarily high mobility of holes that is comparable to electron mobility in conventional semiconductors. The hole conductivity in graphene can be electrostatically tuned in the graphene-2DEG parallel capacitor configuration, thus more efficiently tuning the THz transmission. In this work, we show that it is possible to achieve a modulation depth of > 90% while simultaneously minimizing signal attenuation to < 5% by tuning the Fermi level at the Dirac point in graphene.

cond-mat.mtrl-sci↗