High-performance p-type field-effect transistors using substitutional doping and thickness control of two-dimensional materials | Nature Electronics

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In silicon field-effect transistors (FETs), degenerate doping of the channel beneath the source and drain regions is used to create high-performance n- and p-type devices by reducing the contact resistance. Two-dimensional semiconductors have, in contrast, relied on metal-work-function engineering. This approach has led to the development of effective n-type 2D FETs due to the Fermi-level pinning occurring near the conduction band, but it is challenging with p-type FETs. Here we show that the degenerate p-type doping of molybdenum diselenide and tungsten diselenide—achieved through substitutional doping with vanadium, niobium and tantalum—can reduce the contact resistance to as low as 95 Ω µm in multilayers. This, though, comes at the cost of poor electrostatic control, and we find that the doping effectiveness—and its impact on electrostatic control—is reduced in thinner layers due to strong quantum confinement effects. We, therefore, develop a high-performance p-type 2D molybdenum diselenide FET using a layer-by-layer thinning method to create a device with thin layers at the channel and thick doped layers at the contact regions.

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The data that support the findings of this study are available from the corresponding authors upon reasonable request.

The codes used for plotting the data are available from the corresponding authors upon reasonable request.

Manzeli, S., Ovchinnikov, D., Pasquier, D., Yazyev, O. V. & Kis, A. 2D transition metal dichalcogenides. Nat. Rev. Mater. 2, 17033 (2017).

Article Google Scholar

Bhimanapati, G. R. et al. Recent advances in two-dimensional materials beyond graphene. ACS Nano 9, 11509–11539 (2015).

Article Google Scholar

Choi, W. et al. Recent development of two-dimensional transition metal dichalcogenides and their applications. Mater. Today 20, 116–130 (2017).

Article Google Scholar

Nikonov, D. E. & Young, I. A. Benchmarking of beyond-CMOS exploratory devices for logic integrated circuits. IEEE J. Explor. Solid-State Comput. Devices Circuits 1, 3–11 (2015).

Article Google Scholar

Sylvia, S. S., Alam, K. & Lake, R. K. Uniform benchmarking of low-voltage van der Waals FETs. IEEE J. Explor. Solid-State Comput. Devices Circuits 2, 28–35 (2016).

Article Google Scholar

Lee, C.-S., Cline, B., Sinha, S., Yeric, G. & Wong, H. S. P. 32-bit processor core at 5-nm technology: analysis of transistor and interconnect impact on VLSI system performance. In 2016 IEEE International Electron Devices Meeting (IEDM) 28.3.1–28.3.4 (IEEE, 2016).

Agarwal, T. et al. Benchmarking of monolithic 3D integrated MX2 FETs with Si FinFETs. In 2017 IEEE International Electron Devices Meeting (IEDM) 5.7.1–5.7.4 (IEEE, 2017).

Geng, D. & Yang, H. Y. Recent advances in growth of novel 2D materials: beyond graphene and transition metal dichalcogenides. Adv. Mater. 30, 1800865 (2018).

Article Google Scholar

Sebastian, A., Pendurthi, R., Choudhury, T. H., Redwing, J. M. & Das, S. Benchmarking monolayer MoS2 and WS2 field-effect transistors. Nat. Commun. 12, 693 (2021).

Article Google Scholar

Shen, P.-C. et al. Ultralow contact resistance between semimetal and monolayer semiconductors. Nature 593, 211–217 (2021).

Article Google Scholar

Li, W. et al. Approaching the quantum limit in two-dimensional semiconductor contacts. Nature 613, 274–279 (2023).

Article Google Scholar

English, C. D., Smithe, K. K. H., Xu, R. L. & Pop, E. Approaching ballistic transport in monolayer MoS2 transistors with self-aligned 10 nm top gates. In 2016 IEEE International Electron Devices Meeting (IEDM) 5.6.1–5.6.4 (IEEE, 2016).

Zhang, Y. et al. A single-crystalline native dielectric for two-dimensional semiconductors with an equivalent oxide thickness below 0.5 nm. Nat. Electron. 5, 643–649 (2022).

Article Google Scholar

Li, T. et al. A native oxide high-κ gate dielectric for two-dimensional electronics. Nat. Electron. 3, 473–478 (2020).

Article Google Scholar

Schulman, D. S., Arnold, A. J. & Das, S. Contact engineering for 2D materials and devices. Chem. Soc. Rev. https://doi.org/10.1039/c7cs00828g (2018).

Article Google Scholar

Das, S., Chen, H. Y., Penumatcha, A. V. & Appenzeller, J. High performance multilayer MoS2 transistors with scandium contacts. Nano Lett. 13, 100–105 (2013).

Article Google Scholar

Das, S. and Appenzeller, J. WSe2 field effect transistors with enhanced ambipolar characteristics. Appl. Phys. Lett. 103, 103501 (2013).

Zhang, X. et al. Defect-controlled nucleation and orientation of WSe2 on hBN: a route to single-crystal epitaxial monolayers. ACS Nano https://doi.org/10.1021/acsnano.8b09230 (2019).

Article Google Scholar

Zhang, Z., Guo, Y. & Robertson, J. Origin of weaker Fermi level pinning and localized interface states at metal silicide Schottky barriers. J. Phys. Chem. C 124, 19698–19703 (2020).

Article Google Scholar

Stolz, S. et al. Layer-dependent Schottky contact at van der Waals interfaces: V-doped WSe2 on graphene. npj 2D Mater. Appl. 6, 66 (2022).

Article Google Scholar

Zhu, G.-J., Xu, Y.-G., Gong, X.-G., Yang, J.-H. & Yakobson, B. I. Dimensionality-inhibited chemical doping in two-dimensional semiconductors: the phosphorene and MoS2 from charge-correction method. Nano Lett. 21, 6711–6717 (2021).

Article Google Scholar

Chowdhury, S., Venkateswaran, P. & Somvanshi, D. A systematic study on the electronic structure of 3d, 4d, and 5d transition metal-doped WSe2 monolayer. Superlattices Microstruct. 148, 106746 (2020).

Article Google Scholar

McClellan, C. J., Yalon, E., Smithe, K. K., Suryavanshi, S. V. & Pop, E. High current density in monolayer MoS2 doped by AlOx. ACS Nano 15, 1587–1596 (2021).

Article Google Scholar

Tongay, S. et al. Thermally driven crossover from indirect toward direct bandgap in 2D semiconductors: MoSe2 versus MoS2. Nano Lett. 12, 5576–5580 (2012).

Article Google Scholar

Ghosh, S. K. & Somvanshi, D. First-principal insight of the gold-metal interaction to bilayer MoSe2 of AB and AA stacking order. Solid State Commun. 342, 114613 (2022).

Article Google Scholar

Bhattacharyya, S. & Singh, A. K. Semiconductor-metal transition in semiconducting bilayer sheets of transition-metal dichalcogenides. Phys. Rev. B 86, 075454 (2012).

Article Google Scholar

Gusakova, J. et al. Electronic properties of bulk and monolayer TMDs: theoretical study within DFT framework (GVJ-2e method). Phys. Status Solidi (a) 214, 1700218 (2017).

Article Google Scholar

Kuc, A., Zibouche, N. & Heine, T. Influence of quantum confinement on the electronic structure of the transition metal sulfide TS2. Phys. Rev. B 83, 245213 (2011).

Article Google Scholar

Nasr, J. R., Schulman, D. S., Sebastian, A., Horn, M. W. & Das, S. Mobility deception in nanoscale transistors: an untold contact story. Adv. Mater. 31, 1806020 (2019).

Article Google Scholar

Chou, A.-S. et al. High-performance monolayer WSe2 p/n FETs via antimony-platinum modulated contact technology towards 2D CMOS electronics. In 2022 International Electron Devices Meeting (IEDM) 7.2.1–7.2.4 (IEEE, 2022).

Cai, L. et al. Rapid flame synthesis of atomically thin MoO3 down to monolayer thickness for effective hole doping of WSe2. Nano Lett. 17, 3854–3861 (2017).

Article Google Scholar

Chiang, C.-C., Lan, H.-Y., Pang, C.-S., Appenzeller, J. & Chen, Z. Air-stable P-doping in record high-performance monolayer WSe2 devices. IEEE Electron Device Lett. 43, 319–322 (2021).

Article Google Scholar

Pandey, S. K. et al. Controlled p-type substitutional doping in large-area monolayer WSe2 crystals grown by chemical vapor deposition. Nanoscale 10, 21374–21385 (2018).

Article Google Scholar

Kozhakhmetov, A. et al. Controllable p‐type doping of 2D WSe2 via vanadium substitution. Adv. Funct. Mater. 31, 2105252 (2021).

Article Google Scholar

Vu, V. T. et al. One-step synthesis of NbSe2/Nb-doped-WSe2 metal/doped-semiconductor van der Waals heterostructures for doping controlled ohmic contact. ACS Nano 15, 13031–13040 (2021).

Article Google Scholar

Li, X. et al. Isoelectronic tungsten doping in monolayer MoSe2 for carrier type modulation. Adv. Mater. 28, 8240–8247 (2016).

Article Google Scholar

Zhong, F. et al. Substitutionally doped MoSe2 for high‐performance electronics and optoelectronics. Small 17, 2102855 (2021).

Article Google Scholar

Fang, H. et al. High-performance single layered WSe2 p-FETs with chemically doped contacts. Nano Lett. 12, 3788–3792 (2012).

Article Google Scholar

Pang, C. S. et al. Atomically controlled tunable doping in high‐performance WSe2 devices. Adv. Electron. Mater. 6, 1901304 (2020).

Article Google Scholar

Yamamoto, M., Nakaharai, S., Ueno, K. & Tsukagoshi, K. Self-limiting oxides on WSe2 as controlled surface acceptors and low-resistance hole contacts. Nano Lett. 16, 2720–2727 (2016).

Article Google Scholar

Yang, S., Lee, G. & Kim, J. Selective p-doping of 2D WSe2 via UV/ozone treatments and its application in field-effect transistors. ACS Appl. Mater. Interfaces 13, 955–961 (2020).

Article Google Scholar

Zhang, T. et al. Universal in situ substitutional doping of transition metal dichalcogenides by liquid-phase precursor-assisted synthesis. ACS Nano 14, 4326–4335 (2020).

Article Google Scholar

Pham, Y. T. H. et al. Tunable ferromagnetism and thermally induced spin flip in vanadium‐doped tungsten diselenide monolayers at room temperature. Adv. Mater. 32, 2003607 (2020).

Article Google Scholar

Chou, A. S. et al. High-performance monolayer WSe2 p/n FETs via antimony-platinum modulated contact technology towards 2D CMOS electronics. In 2022 International Electron Devices Meeting (IEDM) 7.2.1–7.2.4 (IEEE, 2022).

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We thank L. J. Liermann for conducting the ICP-AES analysis, J. M. Anderson for conducting the SEM-EDS analysis on the doped crystals and Y. Zheng for assisting in the oxygen plasma treatment of the fabricated devices. Our sincere gratitude also goes to the Penn State Nanofabrication staff and the cleanroom facility at the Materials Research Institute (MRI), Penn State, where all the device fabrication was carried out. The work was supported by the National Science Foundation (NSF) through a CAREER Award under grant no. ECCS-2042154. Z.S. was supported by ERC-CZ programme (project LL2101) from Ministry of Education Youth and Sports (MEYS) and by the project Advanced Functional Nanorobots (reg. no. CZ.02.1.01/0.0/0.0/15_003/0000444 financed by the ERDF). A.P. was supported by a NASA Space Technology Graduate Research Opportunity grant (no. 80NSSC23K1197). K.J.S. was supported by the Johannes Amos Comenius Programme, European Structural and Investment Funds, project CHEMFELLS VI (no. CZ.02.01.01/00/22_010/0008122).

These authors contributed equally: Mayukh Das, Dipanjan Sen.

Engineering Science and Mechanics, Penn State University, University Park, PA, USA

Mayukh Das, Dipanjan Sen, Najam U Sakib, Harikrishnan Ravichandran, Yongwen Sun, Zhiyu Zhang, Subir Ghosh, Pranavram Venkatram, Shiva Subbulakshmi Radhakrishnan, Muhtasim Ul Karim Sadaf, Andrew Pannone, Ying Han, Yang Yang & Saptarshi Das

Department of Physics, Penn State University, University Park, PA, USA

Alexander Sredenschek, Zhuohang Yu, David Emanuel Sanchez & Mauricio Terrones

Department of Inorganic Chemistry, University of Chemistry and Technology Prague, Prague, Czech Republic

Kalyan Jyoti Sarkar, Kalaiarasan Meganathan & Zdenek Sofer

Department of Physics, Harcourt Butler Technical University, Kanpur, India

Divya Somvanshi

Materials Science and Engineering, Penn State University, University Park, PA, USA

Mauricio Terrones & Saptarshi Das

Nuclear Engineering, Penn State University, University Park, PA, USA

Yang Yang

Electrical Engineering, Penn State University, University Park, PA, USA

Yang Yang & Saptarshi Das

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S.D. conceived the idea and designed the experiments. M.D., D. Sen., N.U.S., H.R., P.V., M.U.K.S. and S.S.R. fabricated and measured the devices. Y.S., Z.Z., Y.H. and Y.Y. obtained and analysed the high-resolution cross-sectional TEM data. D.E.S performed the c-axis high-resolution TEM on the doped MoSe2 crystals. A.S., Z.Y. and M.T. grew the Nb-doped MoSe2. K.J.S., K.M. and Z.S. grew the Nb-, V- and Ta-doped MoSe2 and WSe2 crystals. A.P. helped with the AFM measurements. S.G. and D. Somvanshi. performed the DFT simulations. All authors contributed to the preparation of the paper.

Correspondence to Saptarshi Das.

The authors declare no competing interests.

Nature Electronics thanks Ruge Quhe and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Bar plots showing the dopant concentrations for V, Nb, and Ta, determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES) for a) MoSe2 and b) WSe2. Dopant concentrations for V, Nb, and Ta, extracted using scanning electron microscopy-electron dispersive X-ray spectroscopy (SEM-EDS) for c) MoSe2 and d) WSe2. Bulk carrier concentrations (NB) at room temperature, obtained from Hall measurements for e) MoSe2 and f) WSe2 doped with V, Nb, and Ta.

Transfer characteristics for a) two thick (~4–6 monolayers) and b) two thin (~1–3 monolayers) MoSe2 FETs. Transfer characteristics for c) two thick (~4–6 monolayers) and d) two thin (~1–3 monolayers) WSe2 FETs at \({V}_{{DS}}\) = 1 V.

Transfer characteristics, that is, source-to-drain current (\({I}_{{DS}}\)) as a function of the back-gate voltage (\({V}_{{BG}}\)) for a constant source-to-drain bias of \({V}_{{DS}}\) = 1 V for a) V-, b) Nb-, and c) Ta-doped WSe2 FETs with thick (~4–6 monolayers) channels. These FETs show high on-state current (ION) (except for the case of V-doped WSe2) and poor electrostatic gate control (low ION/IOFF) confirming degenerate p-type doping. In contrast, transfer characteristics for d) V-, e) Nb-, and f) Ta-doped WSe2 FETs with thin (~1–3 monolayers) channels retained high ION/IOFF more than 105. However, ION values were significantly lower. Corresponding scatter plots with ION measured at VBG = −15 V and ION/IOFF as the two axes for g) V-, h) Nb-, and i) Ta-doped FETs with thick and thin WSe2 channels. All FETs have a channel length (\({L}_{{CH}}\)) of 500 nm.

In this observation, it is evident that the introduction of V, Nb, and Ta doping results in a reduction of the band gap, and there is also a notable shift of the Fermi level below the valence band.

Hole field-effect mobility (\({\mu }_{{FE}}\)), extracted from peak transconductance for a) thick channel and b) thin channel FETs based on V-, Nb-, and Ta-doped MoSe2 and for c) thick channel and d) thin channel FETs based on V-, Nb-, and Ta-doped WSe2. Bar plots showing the 4-point probe mobility (\({\mu }_{4{PP}}\)) extracted from Hall measurement for holes for e) MoSe2 and f) WSe2 specimens with dopants V, Nb, and Ta.

a) Optical images of MoSe2 flakes taken before and after successive treatment with mild oxygen plasma followed by DI water rinse to remove the top-layer of MoOx. The layer-by-layer thinning is evident from the contrast of the flakes that transitions from a deep brown hue to a lighter shade of brown. b) AFM images of the evolution of layer-by-layer thinning of MoSe2 flakes subjected to O2 plasma. Each plasma step is followed by a DI water dip before subsequent AFM measurements. The height profile of the flake along line 1 is also depicted and reveals a reduction of about 0.8 nm after each plasma step suggesting the removal of a single layer of MoSe2 flake.

Transfer characteristics of a) as-fabricated and b) post-processed Nb-doped MoSe2 FETs with \({L}_{{CH}}\) = 50 nm, 100 nm, 150 nm, 200 nm, and 500 nm. Three successive rounds of oxygen plasma treatment, followed by immersion in DI water, were carried out to reduce the thickness of the channel between the contacts while keeping the channel thicker underneath the contacts. c) Corresponding total resistance \({R}_{T}\) (normalized by width) measured at \({V}_{{BG}}\) = −15 V versus \({L}_{{CH}}\) for as-fabricated and post-processed Nb-doped MoSe2 FETs at \({V}_{{DS}}\) = 1 V.

(a) A resistor network with essential resistance components associated with carrier transport in our proposed 2D FET structure. Schematic and corresponding band-diagrams for MoSe2 based 2D FETs with thick channels underneath the contacts and (b) multilayer, (c) bilayer and (d) monolayer channels between the contacts. The bandgap mismatch between thick and thin MoSe2 layers give rise to an additional energy barrier at the interface between the thinner channel and thicker contact regions. This energy barrier remains relatively small for channels over 2 layers, as the MoSe2 bandgap stays nearly constant. However, the barrier height can increase markedly when the channel becomes monolayer, due to the transition from indirect to direct bandgap between bi-layer and monolayer. This alteration can lead to a considerable increase in RC. (e) Transfer characteristics of a multilayer Nb-doped MoSe2 FET after each etch cycle, and (f) corresponding bar plot of the \({R}_{C}\) values obtained from TLM measurements.

\({\phi }_{{SB}-P}\) values were obtained for pristine, V-, Nb-, and Ta-doped a) MoSe2 and b) WSe2 FETs. c-d) Schematic of band diagrams for intrinsic and heavily p-type doped semiconductors in contact with a metal. e) Band diagram portraying the broadening of the Fermi-Dirac tail with increasing temperature, providing additional holes for tunnelling through the narrower region of the Schottky barrier. The enhanced tunnelling of holes results in a Ohmic like characteristics at higher temperatures. Output characteristics measured at a constant VBG of −8 V as the temperature is increased from 75 K to 300 K. The output characteristics transitioned from mostly Schottky type to nearly Ohmic-like.

Supplementary Figs. 1–10.

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Das, M., Sen, D., Sakib, N.U. et al. High-performance p-type field-effect transistors using substitutional doping and thickness control of two-dimensional materials. Nat Electron (2024). https://doi.org/10.1038/s41928-024-01265-2

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Received: 06 March 2024

Accepted: 24 September 2024

Published: 06 November 2024

DOI: https://doi.org/10.1038/s41928-024-01265-2

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