MoS2 Dual-Gate MOSFET with Atomic-Layer-Deposited Al2O3 as Top-Gate Dielectric

We demonstrate atomic-layer-deposited (ALD) high-k dielectric integration on two-dimensional (2D) layer-structured molybdenum disulfide (MoS2) crystals and MoS2 dual-gate n-channel MOSFETs with ALD Al2O3 as top-gate dielectric. Our C-V study of MOSFET structures shows good interface between 2D MoS2 crystal and ALD Al2O3. Maximum drain currents using back-gates and top-gates are measured to be 7.07mA/mm and 6.42mA/mm at Vds=2V with a channel width of 3 {\mu}m, a channel length of 9 {\mu}m, and a top-gate length of 3 {\mu}m. We achieve the highest field-effect mobility of electrons using back-gate control to be 517 cm^2/Vs. The highest current on/off ratio is over 10^8.Comment: submitted to IEEE Electron Device Letter

Atomic-Layer-Deposited Al2O3 on Bi2Te3 for Topological Insulator Field-Effect Transistors

We report dual-gate modulation of topological insulator field-effect transistors (TI FETs) made on Bi2Te3 thin flakes with integration of atomic-layer-deposited (ALD) Al2O3 high-k dielectric. Atomic force microscopy study shows that ALD Al2O3 is uniformly grown on this layer-structured channel material. Electrical characterization reveals that the right selection of ALD precursors and the related surface chemistry play a critical role in device performance of Bi2Te3 based TI FETs. We realize both top-gate and bottom-gate control on these devices, and the highest modulation rate of 76.1% is achieved by using simultaneous dual gate control.Comment: 4 pages, 3 figure

Electron spin magnetism of zigzag graphene nanoribbon edge states

The electron spin states of zigzag graphene nanoribbon (ZGNR) edge play a pivotal role in the applications of graphene nanoribbons. However, the exact arrangements of the electron spins remain unclear to date. In this report, the electronic spin states of the ZGNR edge have been elucidated through a combination of quantum chemical investigation and previous electron spin resonance experiment observations. An alternating alpha and beta spin configuration of the unpaired electrons along the ZGNR edge is established in ambient condition without any external magnetic field, and the origin of the spin magnetism of the ZGNR edge is revealed. It paves a pathway for the understanding and design of graphene based electronic and spintronic devices. (C) 2014 AIP Publishing LLC

Synthesis and Characterization of 2D Atomic Layers

As electronic devices have continued to become smaller, a pressing need has developed for new technologies in order to surpass current size constraints. As such, 2-dimensional materials have become a topic of great interest in experimental device research. Monolayer black phosphorus, or phosphorene, is one such 2D material which shows significant potential as a p-type semiconductor. Phosphorene exhibits a number of unique and desirable electrical properties such as a layer-dependent band gap, high carrier mobility, and anisotropic conductivity. An investigation into optimal growth of black phosphorus, the precursor material to phosphorene, as well as characterization of phosphorene-based devices will be performed

MoS2 Nanoribbon Transistors: Transition from Depletion-mode to Enhancement-mode by Channel Width Trimming

We study the channel width scaling of back-gated MoS2 metal-oxide-semiconductor field-effect transistors (MOSFETs) from 2 {\mu}m down to 60 nm. We reveal that the channel conductance scales linearly with channel width, indicating no evident edge damage for MoS2 nanoribbons with widths down to 60 nm as defined by plasma dry etching. However, these transistors show a strong positive threshold voltage (VT) shift with narrow channel widths of less than 200 nm. Our results also show that transistors with thinner channel thicknesses have larger VT shifts associated with width scaling. Devices fabricated on a 6 nm thick MoS2 crystal underwent the transition from depletion-mode to enhancement-mode.Comment: 3 pages, 3 figures, to appear in IEEE Electron Device Letter