Molecule‐Upgraded van der Waals Contacts for Schottky‐Barrier‐Free Electronics

Abstract

The applications of any ultrathin semiconductor device are inseparable from high‐quality metal–semiconductor contacts with designed Schottky barriers. Building van der Waals (vdWs) contacts of 2D semiconductors represents an advanced strategy of lowering the Schottky barrier height by reducing interface states, but will finally fail at the theoretical minimum barrier due to the inevitable energy difference between the semiconductor electron affinity and the metal work function. Here, an effective molecule optimization strategy is reported to upgrade the general vdWs contacts, achieving near‐zero Schottky barriers and creating high‐performance electronic devices. The molecule treatment can induce the defect healing effect in p‐type semiconductors and further enhance the hole density, leading to an effectively thinned Schottky barrier width and improved carrier interface transmission efficiency. With an ultrathin Schottky barrier width of ≈2.17 nm and outstanding contact resistance of ≈9 kΩ µm in the optimized Au/WSe2 contacts, an ultrahigh field‐effect mobility of ≈148 cm2 V−1 s−1 in chemical vapor deposition grown WSe2 flakes is achieved. Unlike conventional chemical treatments, this molecule upgradation strategy leaves no residue and displays a high‐temperature stability at >200 °C. Furthermore, the Schottky barrier optimization is generalized to other metal–semiconductor contacts, including 1T‐PtSe2/WSe2, 1T′‐MoTe2/WSe2, 2H‐NbS2/WSe2, and Au/PdSe2, defining a simple, universal, and scalable method to minimize contact resistance.

All‐van‐der‐Waals Barrier‐Free Contacts for High‐Mobility Transistors

“…The hole mobility of ≈97 cm 2 V −1 s –1 of the chemical vapor deposition (CVD)‐grown WSe 2 FET with the 1T′‐WS 2 semimetal contacts (Figure 5d) is much higher than that of ≈20 cm 2 V −1 s –1 of Au contacted WSe 2 FET (Figure 5e). Among them, the mobility of the WSe 2 transistor with evaporated Au contacts is largely consistent with the previously reported value of the WSe 2 transistor with evaporated metal contacts (Table S1, Supporting Information), [ 4,5c,26 ] which suggests the high mobility of the WSe 2 FET with the 1T′‐WS 2 semimetal contact originate the high‐quality contacts not the WSe 2 channel material. Through the variation‐temperature study and the four‐probe resistance measurement (Figure 5f–h), the Schottky barrier height and contacts resistance of this WSe 2 interface were measured to be 50 ± 11 meV and ≈3.07 kΩ µm, respectively.…”

“…The WSe 2 films were deposited by the high‐temperature thermal CVD process. [ 4,29 ] The WSe 2 powder (2–3 g, Alfa Aesar, 99.8% purity) was heated to the temperature of ≈1150 °C, then the gaseous WSe 2 was absorbed on the lower‐temperature SiO 2 /Si substrates near the outlet of the single zone furnace (SK2‐2.5‐15, Tianjin Zhonghuan Furnace Corp), respectively. The specific growth parameters were growth duration of ≈3 min and high‐purity Argon of ≈300 sccm.…”

“…[ 3 ] To avoid such interface states created in the thermal deposition processes of conventional metals, van der Waals (vdW) contacts via transferring metal electrodes are invented to suppress the Fermi‐level pinning in metal/2D‐semiconductor interfaces but still cannot fully address this problem. [ 1a,4 ] Because the decaying metallic wavefunction from conventional metals still introduces the MIGS, resulting in the severe pinning effect of the Fermi‐levels. [ 2a ]…”

Ultrathin Metallic NbS2 Nanosheets with Unusual Intercalation Mechanism for Ultra‐Stable Potassium‐Ion Storage

“…Benefit from the above merits, 2D TMDs show extensive potential in different research fields like electrochemical catalysis, energy storage and conversion, superconductor, transistor and photodetector, solar cells, etc. [10][11][12][13][14][15][16][17] When applied in PIBs, they possess very high theoretical capacity by storing potassium ions with the intercalation-conversion mechanism, that is, the intercalation process and the following conversion reaction at relatively low potential. However, the phase conversion during the conversion process usually results in structural collapse and the ensuing ravage of the transportation pathway between the layers, hampering the electrochemical reaction kinetics.…”

A van der Waals Ferroelectric Tunnel Junction for Ultrahigh‐Temperature Operation Memory

“…[47] High performance of the vdW FTJ can be anticipated due to the high interface quality since the electrical transport property of vdW heterostructure strongly depends on the interface quality. [48][49][50][51] The vdW FTJ and its components were further characterized via Raman spectroscopy, as shown in Figure 2d. Typical Raman signature of MLG (G peak at 1582 cm −1 and 2D peak at 2700 cm −1 ), [52] h-BN (E 2g peak at 1365 cm −1 ), [52] and α-In 2 Se 3 (E symmetry mode, A(LO + TO), A(TO) and A(LO) at 90, 104, 180, and 195 cm −1 , respectively) [53][54][55] are observed in the corresponding Raman spectrum and the heterostructure region.…”