Mahmut Tosun

Lawrence Berkeley National Laboratory

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Ali Javey

University of California, Berkeley

Mark Hettick

University of California, Berkeley

Jeong Seuk Kang

Massachusetts Institute of Technology

Sujay B. Desai

University of California, Berkeley

Daisuke Kiriya

The University of Tokyo

Tania Roy

Zhejiang University of Technology

Angada B. Sachid

Applied Materials (United States)

Surabhi R. Madhvapathy

Northwestern University

Der‐Hsien Lien

National Yang Ming Chiao Tung University

Matin Amani

University of California, Berkeley

Cooperative Institutions

University of California, Berkeley

Lawrence Berkeley National Laboratory

École Polytechnique Fédérale de Lausanne

Material Sciences (United States)

Berkeley College

Kavli Energy NanoScience Institute

University of California System

Australian National University

National Yang Ming Chiao Tung University

Centre National de la Recherche Scientifique

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Gold‐Mediated Exfoliation of Ultralarge Optoelectronically‐Perfect Monolayers

Advanced Materials (2016)

Sujay B. Desai Surabhi R. Madhvapathy Matin Amani Daisuke Kiriya Mark Hettick

Gold-mediated exfoliation of ultralarge optoelectronically perfect monolayers with lateral dimensions up to ≈500 μm is reported. Electrical, optical, and X-ray photo-electron spectroscopy characterization show that the quality of the gold-exfoliated flakes is similar to that of tape-exfoliated flakes. Large-area flakes allow manufacturing of large-area mono-layer transition metal dichalcogenide electronics.

Exfoliation joint

Characterization

10.1002/adma.201506171

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Citations (376)

2D layered materials: From materials properties to device applications

2021 IEEE International Electron Devices Meeting (IEDM) (2015)

Peida Zhao Sujay B. Desai Mahmut Tosun Tania Roy Hui Fang

An overview of material properties and the current state of electronic devices based on 2D layered materials is presented. Atomic scale smoothness, varying band alignment and sizeable bandgaps in the single layer limit make this class of materials very interesting for optoelectronic applications. Scaling effects, doping techniques, contacts and strain engineering of 2D materials are discussed. In addition, important advancements in 2D material electronic devices, for example the all-2D field effect transistor (FET), heterojunction devices, and tunnel diode are highlighted.

10.1109/iedm.2015.7409780

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Citations (16)

Monolithic 3D CMOS Using Layered Semiconductors

Advanced Materials (2016)

Angada B. Sachid Mahmut Tosun Sujay B. Desai Ching‐Yi Hsu Der‐Hsien Lien

Monolithic 3D integrated circuits using transition metal dichalcogenide materials and low-temperature processing are reported. A variety of digital and analog circuits are implemented on two sequentially integrated layers of devices. Inverter circuit operation at an ultralow supply voltage of 150 mV is achieved, paving the way to high-density, ultralow-voltage, and ultralow-power applications.

10.1002/adma.201505113

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Citations (128)

Long-term retention in organic ferroelectric-graphene memories

Applied Physics Letters (2012)

Santosh Raghavan Igor Stolichnov N. Setter Jean-Savin Heron Mahmut Tosun

Long-term stability of high- and low-resistance states in full-organic ferroelectrically gated graphene transistors is an essential prerequisite for memory applications. Here, we demonstrate high retention performance for both memory states with fully saturated time-dependence of the graphene channel resistance. This behavior is in contrast with ferroelectric-polymer-gated silicon field-effect-transistors, where the gap between the two memory states continuously decreases with time. Before reaching saturation, the current decays exponentially as predicted by the retention model based on the charge injection into the interface-adjacent layer. The drain current saturation attests to a high quality of the graphene/ferroelectric interface with low density of charge traps.

Saturation (graph theory)

Retention time

Non-Volatile Memory

10.1063/1.3676055

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Citations (60)

Solid polyelectrolyte-gated surface conductive diamond field effect transistors

Applied Physics Letters (2012)

Markus Dankerl Mahmut Tosun M. Stutzmann José A. Garrido

Solid polyelectrolytes have been used in transistor devices to achieve gating with high capacitance. We use a solid polyethylene oxide/LiClO4 electrolyte to replace aqueous electrolytes as a gate for surface-conductive diamond field-effect transistors (FET). The resulting transistor shows characteristics comparable to those of aqueous electrolyte-gated diamond FETs. We investigate the polyelectrolyte/diamond interface with impedance spectroscopy and cyclic voltammetry, showing the electrochemical stability of the interface and capacitive gating up to 100 Hz. Hall effect measurements on the polyelectrolyte-gated devices are compared to those with liquid gates. The solid and transparent polyelectrolyte gates promise further applications for surface-conductive diamond FETs.

10.1063/1.3676662

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Citations (13)

Air Stable p-Doping of WSe₂ by Covalent Functionalization

ACS Nano (2014)

Peida Zhao Daisuke Kiriya Angelica Azcatl Chenxi Zhang Mahmut Tosun

Covalent functionalization of transition metal dichalcogenides (TMDCs) is investigated for air-stable chemical doping. Specifically, p-doping of WSe2 via NOx chemisorption at 150 °C is explored, with the hole concentration tuned by reaction time. Synchrotron based soft X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) depict the formation of various WSe2–x–yOxNy species both on the surface and interface between layers upon chemisorption reaction. Ab initio simulations corroborate our spectroscopy results in identifying the energetically favorable complexes, and predicting WSe2:NO at the Se vacancy sites as the predominant dopant species. A maximum hole concentration of ∼1019 cm–3 is obtained from XPS and electrical measurements, which is found to be independent of WSe2 thickness. This degenerate doping level facilitates 5 orders of magnitude reduction in contact resistance between Pd, a common p-type contact metal, and WSe2. More generally, the work presents a platform for manipulating the electrical properties and band structure of TMDCs using covalent functionalization.

Surface Modification

10.1021/nn5047844

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Citations (228)

Engineering Light Outcoupling in 2D Materials

Nano Letters (2015)

Der‐Hsien Lien Jeong Seuk Kang Matin Amani Kevin Chen Mahmut Tosun

When light is incident on 2D transition metal dichalcogenides (TMDCs), it engages in multiple reflections within underlying substrates, producing interferences that lead to enhancement or attenuation of the incoming and outgoing strength of light. Here, we report a simple method to engineer the light outcoupling in semiconducting TMDCs by modulating their dielectric surroundings. We show that by modulating the thicknesses of underlying substrates and capping layers, the interference caused by substrate can significantly enhance the light absorption and emission of WSe2, resulting in a ∼11 times increase in Raman signal and a ∼30 times increase in the photoluminescence (PL) intensity of WSe2. On the basis of the interference model, we also propose a strategy to control the photonic and optoelectronic properties of thin-layer WSe2. This work demonstrates the utilization of outcoupling engineering in 2D materials and offers a new route toward the realization of novel optoelectronic devices, such as 2D LEDs and solar cells.

Light emission

10.1021/nl504632u

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Citations (146)

MoS₂ P-type Transistors and Diodes Enabled by High Work Function MoO_x Contacts

Nano Letters (2014)

Steven S.C. Chuang Corsin Battaglia Angelica Azcatl Stephen McDonnell Jeong Seuk Kang

The development of low-resistance source/drain contacts to transition-metal dichalcogenides (TMDCs) is crucial for the realization of high-performance logic components. In particular, efficient hole contacts are required for the fabrication of p-type transistors with MoS2, a model TMDC. Previous studies have shown that the Fermi level of elemental metals is pinned close to the conduction band of MoS2, thus resulting in large Schottky barrier heights for holes with limited hole injection from the contacts. Here, we show that substoichiometric molybdenum trioxide (MoOx, x < 3), a high work function material, acts as an efficient hole injection layer to MoS2 and WSe2. In particular, we demonstrate MoS2 p-type field-effect transistors and diodes by using MoOx contacts. We also show drastic on-current improvement for p-type WSe2 FETs with MoOx contacts over devices made with Pd contacts, which is the prototypical metal used for hole injection. The work presents an important advance in contact engineering of TMDCs and will enable future exploration of their performance limits and intrinsic transport properties.

Molybdenum trioxide

Contact resistance

10.1021/nl4043505

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Citations (520)

3D-CMOS-TMDs AdvancedMaterials-2016-SI

Angada B. Sachid Mahmut Tosun Sujay B. Desai Ching-Yi Hsu Der‐Hsien Lien

Source

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Air-Stable n-Doping of WSe₂ by Anion Vacancy Formation with Mild Plasma Treatment

ACS Nano (2016)

Mahmut Tosun Leslie Chan Matin Amani Tania Roy Geun Ho Ahn

Transition metal dichalcogenides (TMDCs) have been extensively explored for applications in electronic and optoelectronic devices due to their unique material properties. However, the presence of large contact resistances is still a fundamental challenge in the field. In this work, we study defect engineering by using a mild plasma treatment (He or H2) as an approach to reduce the contact resistance to WSe2. Material characterization by X-ray photoelectron spectroscopy, photoluminescence, and Kelvin probe force microscopy confirm defect-induced n-doping, up to degenerate level, which is attributed to the creation of anion (Se) vacancies. The plasma treatment is adopted in the fabrication process flow of WSe2 n-type metal-oxide-semiconductor field-effect transistors to selectively create anion vacancies at the metal contact regions. Due to lowering the metal contact resistance, improvements in the device performance metrics such as a 20× improvement in ON current and a nearly ideal subthreshold swing value of 66 mV/dec are observed. This work demonstrates that defect engineering at the contact regions can be utilized as a reliable scheme to realize high-performance electronic and optoelectronic TMDC devices.

Contact resistance

10.1021/acsnano.6b02521

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Citations (229)