Low-resistivity metal-semiconductor (M-S) contact is one of the urgent challenges in the research of 2D transition metal dichalcogenides (TMDs). Here, we report a chloride molecular doping technique which greatly reduces the contact resistance (Rc) in the few-layer WS2 and MoS2. After doping, the Rc of WS2 and MoS2 have been decreased to 0.7 kΩ·μm and 0.5 kΩ·μm, respectively. The significant reduction of the Rc is attributed to the achieved high electron-doping density, thus a significant reduction of Schottky barrier width. As a proof-of-concept, high-performance few-layer WS2 field-effect transistors (FETs) are demonstrated, exhibiting a high drain current of 380 μA/μm, an on/off ratio of 4 × 10(6), and a peak field-effect mobility of 60 cm(2)/(V·s). This doping technique provides a highly viable route to diminish the Rc in TMDs, paving the way for high-performance 2D nanoelectronic devices.

and PMOS (AQi is negligible. However, AVfb does not reach OV We report here for the first time that Fermi pinning at the because Si-Hf and Si-0-Hf bonds co-exist at the polySi interface. The polySilmetal oxide interface causes high threshold voltages in AVfb saturation value depends only on the bond number ratio. A MOSFET devices. Results indicate that pinning occurs due to the comparison of AVfb for HfOz (ALD or MOCVD) and HfSixOy interfacial Si-Hf and Si-0-AI bonds for HfO, and AIzO,, respectively. (MOCVD) films deposited with different precursors and dopant This fundamental characteristic also affects the observed polySi activation anneals produce, the universal curve in Fig. 11. The slight depletion. Device data and simulation results will be presented. variation in AVb for Hf02 can be attributed to differences in Keywords: Hf02, AI203, Fermi pinning, polYd, gate dielectric. processing conditions. Our data indicates that the shifts of Vfb(n+) INTRODUCTION and Vfb(pt) from the characteristic values for SiO, NMOS and Scaling MOSFETs to improve performance results in PMOS are a fundamental characteristic of the PolySilMeOx interface. higher gate leakage as the SiOz gate melectic becomes thinner. To These shifts are responsible for the observed high Vts. address this issue, there has been much interest in hafnium-based The impact of the sub-monolayer HfOz on the CETacc is dielectrics as a potential gate dielectric [1-3]. Two major issues shown in Figs. 12 and 13. Although the p+ gate CETacc increases evident in numerous publications [1-3] that must be addressed to with each subsequent cycle, the n+ gate has a CETacc minimum at IO fabricate useful devices for CMOS circuit applications are (1) the cycles, The n+ gate is in depletion and the minimum indicates Si-Hf high threshold voltages and (2) the large CETinv difference between bonds reduce the polySi depletion. To investigate this further, CMOS NMOS and PMOS. To date, a PolySiIMeOx CMOS process with devices were fabricated (Fig. 14). The polySi depletion for ntgate acceptable Vts for both NMOS and PMOS has not been reported. NMOS (p+ gate PMOS) is decreased (increased) when SiOz is capped Defects and charge within the gatestack (Fig. I ) can result with HfO,. This tradeoff in polySi depletion is attributed to Fermi in substantial Vt shifts. At the top interface, Fermi pinning is a pinning near (Fig. 8). Less band bending occurs for n+ polySi mechanism known to cause high Vts for metal gates [41. Considering because the polySi interface is pinned close to the bulk polySi Fermi the polySi/MeOx interface shown in Fig. 2, the question arises, 'Are level. For p+ gates, more band bending occurs because the interface is the metal atoms at the interface part of the dielectric or part of the pinned further away from the bulk. This effect occurs for low and gate electrode?' This raises the issue as to whether the interface bonds high temperame activation anneals (Fig. 15). This effect is the likely affect the Vt. In this work, we examine the role of the polySiIMeOx cause...

The response of a C60 molecule to manipulation across a surface displays a long range periodicity which corresponds to a rolling motion. A period of three or four lattice constants is observed and is accompanied by complex subharmonic structure due to molecular hops through a regular, repeating sequence of adsorption states. Combining experimental data and ab initio calculations, we show that this response corresponds to a rolling motion in which two of the four Si-C60 covalent bonds act as a pivot over which the molecule rotates while moving through one lattice constant and identify a sequence of C60 bonding configurations that accounts for the periodic structure.

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