P. D. Ye

Purdue University, West Lafayette, Indiana, United States

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Publications (205)482.89 Total impact

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    ABSTRACT: Layered two-dimensional (2D) semiconducting transition metal dichalcogenides (TMD) have been widely isolated, synthesized, and characterized recently. Numerous 2D materials are identified as the potential candidates as channel materials for future thin film technology due to their high mobility and the exhibiting bandgaps. While many TMD filed-effect transistors (FETs) have been widely demonstrated along with a significant progress to clearly understand the device physics, large contact resistance at metal/semiconductor interface still remain a challenge. From 2D device research point of view, how to minimize the Schottky barrier effects on contacts thus reduce the contact resistance of metals on 2D materials is very critical for the further development of the field. Here, we present a review of contact research on molybdenum disulfide and other TMD FETs from the fundamental understanding of metal-semiconductor interfaces on 2D materials. A clear contact research strategy on 2D semiconducting materials is developed for future high-performance 2D FETs with aggressively scaled dimensions.
    APL Materials. 10/2014; 2(9).
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    Han Liu, Yuchen Du, Yexin Deng, Peide D. Ye
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    ABSTRACT: Phosphorus is one of the most abundant elements preserved in earth, and it comprises a fraction of 0.1% of the earth crust. In general, phosphorus has several allotropes, and the two most commonly seen allotropes, i.e. white and red phosphorus, are widely used in explosives and safety matches. In addition, black phosphorus, though rarely mentioned, is a layered semiconductor and has great potential in optical and electronic applications. Remarkably, this layered material can be reduced to one single atomic layer in the vertical direction owing to the van der Waals structure, and is known as phosphorene, in which the physical properties can be tremendously different from its bulk counterpart. In this review article, we trace back to the research history on black phosphorus of over 100 years from the synthesis to material properties, and extend the topic from black phosphorus to phosphorene. The physical and transport properties are highlighted for further applications in electronic and optoelectronics devices.
    Chemical Society Reviews 10/2014; · 24.89 Impact Factor
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    ABSTRACT: 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 kohm*um and 0.5 kohm*um, respectively. The significant reduction of the Rc is attributed to the achieved high electron doping density thus significant reduction of Schottky barrier width. As a proof-ofconcept, high-performance few-layer WS2 field-effect transistors (FETs) are demonstrated, exhibiting a high drain current of 380 uA/um, an on/off ratio of 4*106, and a peak field-effect mobility of 60 cm2/V*s. This doping technique provides a highly viable route to diminish the Rc in TMDs, paving the way for high-performance 2D nano-electronic devices.
    Nano letters. 10/2014;
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    ABSTRACT: This letter evaluates temporal and thermal stability of a state-of-the-art few-layer phosphorene MOSFET with Al2O3 surface passivation and Ti/Au top gate. As fabricated, the phosphorene MOSFET was stable in atmosphere for at least 100 h. With annealing at 200{\deg}C in dry nitrogen for 1 h, its drain current increased by an order of magnitude to approximately 100 mA/mm, which could be attributed to the reduction of trapped charge in Al2O3 and/or Schottky barrier at the source and drain contacts. Thereafter, the drain current was stable between -50{\deg}C and 150{\deg}C up to at least 1000 h. These promising results suggest that environmental protection of phosphorene should not be a major concern, and passivation of phosphorene should focus on its effect on electronic control and transport as in conventional silicon MOSFETs. With cutoff frequencies approaching the gigahertz range, the present phosphorene MOSFET, although far from being optimized, can meet the frequency and stability requirements of most flexible electronics for which phosphorene is intrinsically advantageous due to its corrugated lattice structure.
    10/2014;
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    Yuchen Du, Han Liu, Yexin Deng, Peide D. Ye
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    ABSTRACT: Although monolayer black phosphorus (BP) or phosphorene has been successfully exfoliated and its optical properties have been explored, most of electrical performance of the devices is demonstrated on few-layer phosphorene and ultra-thin BP films. In this paper, we study the channel length scaling of ultra-thin BP field-effect transistors (FETs), and discuss a scheme for using various contact metals to change transistor characteristics. Through studying transistor behaviors with various channel lengths, the contact resistance can be extracted from the transfer length method (TLM). With different contact metals, we find out that the metal/BP interface has different Schottky barrier heights, leading to a significant difference in contact resistance, which is quite different from previous studies of transition metal dichalcogenides (TMDs) such as MoS2 where Fermi-level is strongly pinned near conduction band edge at metal/MoS2 interface. The nature of BP transistors are Schottky barrier FETs, where the on and off states are controlled by tuning the Schottky barriers at the two contacts. We also observe the ambipolar characteristics of BP transistors with enhanced n-type drain current and demonstrate that the p-type carriers can be easily shifted to n-type or vice versus by controlling the gate bias and drain bias, showing the potential to realize BP CMOS logic circuits.
    ACS nano. 08/2014;
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    Adam T. Neal, Yuchen Du, Han Liu, Peide D. Ye
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    ABSTRACT: We have determined the spin-orbit scattering length of two-dimensional layered 2H-TaSe2 metallic crystals by detailed characterization of the weak anti-localization phenomena in this strong spin-orbit interaction material. By fitting the observed magneto-conductivity, the spin-orbit scattering length for 2H-TaSe2 is determined to be 17 nm in the few-layer films. This small spin-orbit scattering length is comparable to that of Pt, which is widely used to study the spin Hall effect, and indicates the potential of TaSe2 for use in spin Hall effect devices. In addition to strong spin-orbit coupling, a material must also support large charge currents to achieve spin-transfer-torque via the spin Hall effect. Therefore, we have characterized the room temperature breakdown current density of TaSe2 in air, where the best breakdown current density reaches 3.7$\times$10$^7$ A/cm$^2$. This large breakdown current further indicates the potential of TaSe2 for use in spin-torque devices and two-dimensional device interconnect applications.
    ACS Nano 08/2014; · 12.03 Impact Factor
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    ABSTRACT: Phosphorene, an elemental 2D material, which is the monolayer of black phosphorus, has been mechanically exfoliated recently. In its bulk form, black phosphorus shows high carrier mobility (~10000 cm2/V•s) and a ~0.3 eV direct bandgap. Well-behaved p-type field-effect transistors with mobilities of up to 1000 cm2/V•s, as well as phototransistors, have been demonstrated on few-layer black phosphorus, showing its promise for electronics and optoelectronics applications due to its high mobility and thickness-dependence direct bandgap. However, p-n junctions, the basic building blocks of modern electronic and optoelectronic devices, have not yet been realized based on black phosphorus. In this letter, we demonstrate a gate tunable p-n diode based on a p-type black phosphorus/n-type monolayer MoS2 van der Waals p-n heterojunction. Upon illumination, these ultra-thin p-n diodes show a maximum photodetection responsivity of 418 mA/W at the wavelength of 633 nm, and photovoltaic energy conversion with an external quantum efficiency of 0.3%. These p-n diodes show promise for broadband photodetection and solar energy harvesting.
    ACS Nano 07/2014; · 12.03 Impact Factor
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    ABSTRACT: In this paper, we report a novel chemical doping technique to reduce the contact resistance (Rc) of transition metal dichalcogenides (TMDs) - eliminating two major roadblocks (namely, doping and high Rc) towards demonstration of high-performance TMDs field-effect transistors (FETs). By using 1,2 dichloroethane (DCE) as the doping reagent, we demonstrate an active n-type doping density > 2*1019 cm-3 in a few-layer MoS2 film. This enabled us to reduce the Rc value to a record low number of 0.5 kohm*um, which is ~10x lower than the control sample without doping. The corresponding specific contact resistivity (pc) is found to decrease by two orders of magnitude. With such low Rc, we demonstrate 100 nm channel length (Lch) MoS2 FET with a drain current (Ids) of 460 uA/um at Vds = 1.6 V, which is twice the best value reported so far on MoS2 FETs.
    06/2014;
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    ABSTRACT: InAs gate-all-around (GAA) nanowire MOSFETs are experimentally demonstrated for the first time by a top-down approach [1-3]. Thanks to the well-controlled nanowire release process and the novel ALD high-k/metal gate stack process, InAs nFETs with channel length (Lch) ranging from 380 to 20 nm and nanowire width (WNW) from 60 to 20 nm are achieved. With an EOT of 3.9 nm, high drain current of 4.3 A/mm at Vds = Vgs = 2 V and maximum transconductance (gmax) of 1.6 S/mm at Vds = 1 V are obtained in a device with WNW = 20 nm and Lch = 180 nm, normalized by the perimeter of the nanowires. A detailed scalability study (VTH, gm, Ids vs. Lch) was carried out. The devices in this study show strong dependence on the nanowire width and smaller nanowire size offers much enhanced electrical performance and better immunity from the short channel effects (SCEs).
    2014 72nd Annual Device Research Conference (DRC); 06/2014
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    ABSTRACT: Although ultra-scaled III-V Gate-all-around (GAA) nanowire (NW) MOSFETs have been studied for their immunity to short channel effects, the degradation mechanisms, such as, hot carrier injection (HCI) in the NW MOSFETs are yet to be studied systematically. In this paper, we examine how HCI affects the NW device performance (ΔVth, ΔSS in both stress and recovery) at different bias conditions, and demonstrate that, unlike positive bias temperature instability (PBTI) in NMOS transistors, the HCI degradation is dominated by charge trapping. We analyze the implications of spatial charge trapping on device performance through experiments and simulation. We find that the distinctive features of HCI degradation of GAA NWs structure can be consistently interpreted by a Sentaurus™-based TCAD simulation.
    2014 IEEE International Reliability Physics Symposium (IRPS); 06/2014
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    ABSTRACT: Based on the multiple subbands quasi-ballistic transport theory, we investigate the electronic transport of nano size In0.53Ga0.47As nFinFETs with Al2O3 gate dielectric, emphasizing the saturation current region. 1D mobile charge density and gate capacitance density are introduced for the first time to describe the nano-FinFET transport property under volume inversion. With the extracted effective channel mobility of electrons in the linear region from our experiments, the electron mean free path λ in the channel with the value of 5–9 nm is obtained. With only one fitting parameter α = 0.31 for the critical length in the quasi-ballistic transport theory, the calculated drain current can fit all experimental data for various gate voltage V g, source–drain voltage V d, and temperature (240–332 K) in overall very good agreement. The backscattering coefficient r in the saturation region is larger than 0.8, indicating a large room for improvement for the present InGaAs FinFET technology and performance.
    Semiconductor Science and Technology 05/2014; 29(7):075014. · 1.92 Impact Factor
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    ABSTRACT: Phosphorene is a unique single elemental semiconductor with two-dimensional layered structures. In this letter, we study the transistor behavior on mechanically exfoliated few-layer phosphorene with the top-gate. We achieve a high on-current of 144 mA/mm and hole mobility of 95.6 cm2/Vs. We deposit Al2O3 by atomic layer deposition (ALD) and study the effects of dielectric capping. We observe that the polarity of the transistors alternated from p-type to ambipolar with Al2O3 grown on the top. We attribute this transition to the changes for the effective Schottky barrier heights for both electrons and holes at the metal contact edges, which is originated from fixed charges in the ALD dielectric.
    IEEE Electron Device Letters 05/2014; 35(7). · 2.79 Impact Factor
  • Kun Xu, Peide D. Ye
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    ABSTRACT: Graphene nanoribbons (GNRs), as an emerging class of material, hold great potential for the future high speed and low power electronic and spintronic devices. The fabrication of GNRs is of the utmost interest in terms of graphene based device research. Chemical narrowing of GNRs by oxidation is a promising technique in producing nanoribbons of desired widths. In this article, we hope to elucidate the etching mechanism of zigzag GNR (ZGNR) edge by oxidation through theoretical investigations. The oxidation mechanisms and dynamics of the ZGNR edge by O2 and O3 are fully revealed by density functional theory and statistical theory. The relationship between the reaction time and pressure as well as temperature is estimated dynamically. These theoretical results successfully interpret the recent experimental results and can be further used to predict the appropriate oxidation conditions for the precision etching of ZGNRs.
    The Journal of Physical Chemistry C. 05/2014; 118(19):10400–10407.
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    ABSTRACT: We report a micro-Raman-based optical method to measure in-plane thermal conductivity of ultrathin films. With the use of 20-nm-thick SiO2 substrates that assure in-plane heat transfer, sub-100-nm Bi films and Al2O3 films as thin as 5 nm were successfully measured. The results of Bi films reveal that phonon boundary scattering, both at the surface/interface and at the grain boundaries, reduces in-plane lattice thermal conductivity. The measurements of amorphous Al2O3 films were accomplished using thin Bi film as a Raman temperature sensor, and the results agree with the minimum thermal conductivity models for dielectrics. Our work demonstrates that the micro-Raman method is promising for characterization of in-plane thermal conductivity and phonon behaviors of thin-film structures if the Raman temperature sensor material and substrate material are carefully selected.
    Nanoscale and Microscale Thermophysical Engineering 04/2014; 18(2):183-193. · 1.33 Impact Factor
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    ABSTRACT: We introduce the 2D counterpart of layered black phosphorus, which we call phosphorene, as an unexplored p-type semiconducting material. Same as graphene and MoS2, single-layer phosphorene is flexible and can be mechanically exfoliated. We find phosphorene to be stable and, unlike graphene, to have an inherent, direct, and appreciable band gap. Our ab initio calculations indicate that the band gap is direct, depends on the number of layers and the in-layer strain, and is significantly larger than the bulk value of 0.31-0.36 eV. The observed photoluminescence peak of single-layer phosphorene in the visible optical range confirms that the band gap is larger than that of the bulk system. Our transport studies indicate a hole mobility that reflects the structural anisotropy of phosphorene and complements n-type MoS2. At room temperature, our few-layer phosphorene field-effect transistors with 1.0 μm channel length display a high on-current of 194 mA/mm, a high hole field-effect mobility of 286 cm(2)/V·s, and an on/off ratio of up to 10(4). We demonstrate the possibility of phosphorene integration by constructing a 2D CMOS inverter consisting of phosphorene PMOS and MoS2 NMOS transistors.
    ACS Nano 03/2014; · 12.03 Impact Factor
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    ABSTRACT: For the first time, n-type few-layer MoS2 field-effect transistors with graphene/Ti as the hetero-contacts have been fabricated, showing more than 160 mA/mm drain current at 1 {\mu}m gate length with an on-off current ratio of 107. The enhanced electrical characteristic is confirmed in a nearly 2.1 times improvement in on-resistance and a 3.3 times improvement in contact resistance with hetero-contacts compared to the MoS2 FETs without graphene contact layer. Temperature dependent study on MoS2/graphene hetero-contacts has been also performed, still unveiling its Schottky contact nature. Transfer length method and a devised I-V method have been introduced to study the contact resistance and Schottky barrier height in MoS2/graphene /metal hetero-contacts structure.
    03/2014; 35(5).
  • Kun Xu, Peide D. Ye
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    ABSTRACT: 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 α and β 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.
    Applied Physics Letters 01/2014; 104(16):163104-163104-4. · 3.52 Impact Factor
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    ABSTRACT: Preceding the current interest in layered materials for electronic applications, research in the 1960's found that black phosphorus combines high carrier mobility with a fundamental band gap. We introduce its counterpart, dubbed few-layer phosphorene, as a new 2D p-type material. Same as graphene and MoS2, phosphorene is flexible and can be mechanically exfoliated. We find phosphorene to be stable and, unlike graphene, to have an inherent, direct and appreciable band-gap that depends on the number of layers. Our transport studies indicate a carrier mobility that reflects its structural anisotropy and is superior to MoS2. At room temperature, our phosphorene field-effect transistors with 1.0 um channel length display a high on-current of 194 mA/mm, a high hole field-effect mobility of 286 cm2/Vs, and an on/off ratio up to 1E4. We demonstrate the possibility of phosphorene integration by constructing the first 2D CMOS inverter of phosphorene PMOS and MoS2 NMOS transistors.
    12/2013;
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    ABSTRACT: In this article, we study the metal contact properties on single-layer molybdenum disulfide (MoS2) crystals, and hence reveal the nature of switching mechanism in MoS2 transistors. On investigating transistor behavior with various contact length, we find out that the contact resistivity for metal/MoS2 junctions is defined by contact area instead of contact width. The minimum gate dependent transfer length is ~0.63 μm at on-state for metal (Ti) contacted single-layer MoS2. This reveals the nature for MoS2 transistors is a Schottky barrier transistor, where the on/off states are switched by the tuning the Schottky barriers at contacts. The effective barrier height for drain and source barrier are separately controlled by gate and drain biases. We discuss the drain induced barrier narrowing effect at short channel regions, which may reduce the influence from large contact resistance for MoS2 Schottky barrier transistors at the channel length scaling limit.
    ACS Nano 12/2013; · 12.03 Impact Factor
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    ABSTRACT: Furthering Si CMOS scaling requires development of high-mobility channel materials and advanced device structures to improve the electrostatic control. We demonstrate the fabrication of gate-all-around (GAA) indium gallium arsenide (InGaAs) MOSFETs with highly scaled atomic-layer-deposited gate dielectrics. InGaAs, with its high electron mobility, allows higher drive currents and other on-state performance compared to silicon. The GAA structure provides superior electrostatic control of the MOSFET channel with outstanding off-state performance. A subthreshold slope of 72 mV/dec, electron mobility of 764 cm2/V·s, and an on-current of 1.59 mA/μm are demonstrated, for example. Variability studies on on-state and off-state performances caused by the number of nanowire channels are also presented.
    IEEE Transactions on Device and Materials Reliability 12/2013; 13(4):489-496. · 1.52 Impact Factor

Publication Stats

2k Citations
482.89 Total Impact Points

Institutions

  • 2005–2014
    • Purdue University
      • • Department of Electrical and Computer Engineering Technology (ECET)
      • • School of Electrical and Computer Engineering
      • • Birck Nanotechnology Center
      West Lafayette, Indiana, United States
  • 2011
    • University of Texas at Dallas
      • Department of Materials Science & Engineering
      Dallas, TX, United States
  • 2010
    • University of Padova
      • Department of Information Engineering
      Padova, Veneto, Italy
  • 2004
    • Princeton University
      • Department of Electrical Engineering
      Princeton, NJ, United States
  • 2002–2004
    • Florida State University
      • Department of Physics
      Tallahassee, Florida, United States
  • 2001–2004
    • National High Magnetic Field Laboratory
      Tallahassee, Florida, United States