P. D. Ye

Purdue University, West Lafayette, Indiana, United States

Are you P. D. Ye?

Claim your profile

Publications (188)453.74 Total impact

  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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;
  • [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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
    [Show abstract] [Hide abstract]
    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.
  • [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    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
    [Show abstract] [Hide abstract]
    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. · 3.79 Impact Factor
  • [Show abstract] [Hide abstract]
    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;
  • Source
    [Show abstract] [Hide abstract]
    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
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: For the first time, polyethyleneimine (PEI) doping on multilayer MoS2 field-effect transistors are investigated. A 2.6 times reduction in sheet resistance, and 1.2 times reduction in contact resistance have been achieved. The enhanced electrical characteristics are also reflected in a 70% improvement in ON current, and 50% improvement in extrinsic field-effect mobility. The threshold voltage also confirms a negative shift upon the molecular doping. All studies demonstrate the feasibility of PEI molecular doping in MoS2 transistors, and its potential applications in layer-structured semiconducting 2D crystals.
    IEEE Electron Device Letters 07/2013; 34(10). · 2.79 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have characterized phase coherence length, spin orbit scattering length, and the Hall factor in n-type MoS2 2D crystals via weak localization measurements and Hall-effect measurements. Weak localization measurements reveal a phase coherence length of ~50 nm at T = 400 mK, decreasing as T-1/2 with increased temperatures. Weak localization measurements also allow us, for the first time without optical techniques, to estimate the spin orbit scattering length to be 500 nm, pointing to the potential of MoS2 for spintronics applications. Via Hall-effect measurements, we observe a low temperature Hall mobility of 311 cm2/Vs at T = 1 K which decreases as a power law with a characteristic exponent γ=1.5 from 10 K to 60 K. At room temperature, we observe Hall mobility of 24 cm2/Vs. By determining the Hall factor for MoS2 to be 1.35 at T = 1 K and 2.4 at room temperature, we observe drift mobility of 420 cm2/Vs and 56 cm2/Vs at T = 1 K and room temperature, respectively.
    ACS Nano 07/2013; · 12.03 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Monolayer Molybdenum Disulfide (MoS2) with a direct band gap of 1.8 eV is a promising two-dimensional material with a potential to surpass graphene in next generation nanoelectronic applications. In this letter, we synthesize monolayer MoS2 on Si/SiO2 substrate via chemical vapor deposition (CVD) method and comprehensively study the device performance based on dual-gated MoS2 field-effect transistors. Over 100 devices are studied to obtain a statistical description of device performance in CVD MoS2. We examine and scale down the channel length of the transistors to 100 nm and achieve record high drain current of 62.5 mA/mm in CVD monolayer MoS2 film ever reported. We further extract the intrinsic contact resistance of low work function metal Ti on monolayer CVD MoS¬2 with an expectation value of 175 Ω·mm, which can be significantly decreased to 10 Ω·mm by appropriate gating. Finally, field-effect mobilities (μFE) of the carriers at various channel lengths are obtained. By taking the impact of contact resistance into account, an average and maximum intrinsic μFE is estimated to be 13.0 and 21.6 cm2/Vs in monolayer CVD MoS2 films, respectively.
    Nano Letters 05/2013; · 13.03 Impact Factor
  • IEEE Electron Device Letters 04/2013; 34(4):487-489. · 2.79 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: InGaAs gate-all-around metal-oxide-semiconductor field-effect transistors (MOSFETs) with 6 nm nanowire thickness have been experimentally demonstrated at sub-80 nm channel length. The effects of forming gas anneal (FGA) on the performance of these devices have been systematically studied. The 30 min 400 °C FGA (4% H2/96% N2) is found to improve the quality of the Al2O3/InGaAs interface, resulting in a subthreshold slope reduction over 20 mV/dec (from 117 mV/dec in average to 93 mV/dec). Moreover, the improvement of interface quality also has positive impact on the on-state device performance. A scaling metrics study has been carried out for FGA treated devices with channel lengths down to 20 nm, indicating excellent gate electrostatic control. With the FGA passivation and the ultra-thin nanowire structure, InGaAs MOSFETs are promising for future logic applications.
    Applied Physics Letters 03/2013; 102(9). · 3.79 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Graphene has been identified as a promising material for future spintronics devices due to its low spin orbit coupling and long spin diffusion lengths, even at room temperature [1-2]. However, any device application requires the use of large-area graphene compatible with wafer-scale manufacturing methods, such as graphene grown epitaxially on SiC. We study spin transport in epitaxial graphene grown on SiC (0001) as a step toward future spintronics devices. A non-local spin valve signal of 200mφ is observed at 77K, with a signal of 50mφ resolved at 145K. Assuming a contact polarization of 10% [1], the measured signal corresponds to a spin diffusion length of 130nm at T=77K. Hanle effect spin precession measurements are ongoing. [1] Tombros et al. Nature 448 571 (2007) [2] Maassen et al. Nano Lett. 12, 1498 (2012)
    03/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Semiconducting 2-D crystals, such as MoS2, WSe2, are viewed as promising candidates for electronic applications for their high carrier mobility, thermal stability, compatibility to CMOS process, and superior immunity to short channel effects. However, with the difficulty in ion implantation, the metal contacts on 2-D crystals are yet with large contact resistance, thus eliminates further device performance. We study different metal contacts from low work function to high work function metals on MoS2 and WSe2 crystals with various thicknesses and discuss the Fermi level pinning at the metal/semiconductor interface. Effective Schottky Barrier Heights (SBHs) are also measured. Molecular doping and dual-side contacts metals are performed as two tentative solutions to reduce the effective SBHs, and high-performance of field effect transistors are achieved by reduced contact resistance.
    03/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Advancing toward the rational design, fabrication, and implementation of graphene(GR)-based electronic and optical devices, the intrinsic barrier height of undoped GR (the Dirac point of GR to the conduction band(CB) edge of an insulator), as well as the intrinsic work function(WF) of GR must be accurately determined. We present an internal photoemission (IPE) investigation of a unique semi-transparent metal/high-k/GR/SiO2/Si structure, and focus our study on the photoemission phenomena at the GR/SiO2 interface. By taking advantage of the optical interference of the SiO2 cavity, the enhanced photoemission from GR was observed. As a result, a complete electronic band alignment at the GR/SiO2/Si interfaces is established. The intrinsic positions of the undoped GR Dirac point with respect to the CB of SiO2, 3.58 eV (Al2O3 TG) and 3.60 eV (HfO2 TG), are obtained. The intrinsic WF of graphene is found to be 4.50 eV. The determination of the WF of GR is of significant importance to the engineering of GR-base devices and the IPE spectroscopy, combined with specific interference cavity structures, would be a valuable measurement technique for other GR-like2-D material systems.
    03/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: With the recent identification of the indirect to direct bandgap transition for monolayer MoS2 [1] and the use of MoS2 in field-effect transistors [2,3], this material has attracted recent interest in the physics and nanotechnology communities. We report studies of transport in MoS2 at low temperature from 1K up to 70K, characterized by Hall mobility and weak localization. We find that the mobility at T=400mK in this few-layer MoS2 flake varies from 50cm^2/Vs to 300cm^2/Vs as electron density varies from 6x10^12 cm-2 to 1.2x10^13 cm-2 via the back gate bias. Additionally, we find that the mobility decreases with increasing temperature as a power law with a characteristic exponent of 1.6 at a carrier concentration of 1.2x10^13 cm-2. Magneto-transport measurements reveal weak localization in this MoS2 sample up to temperatures as high as 10K. The phase coherence length in MoS2 is estimated to be about 40nm at 1K for a carrier concentration of 1.2x10^13 cm-2.[4pt] [1] K. F. Mak et al. PRL, 105, 136805 (2010)[0pt] [2] B. Radisavljevic et al. Nature Nano, 6, 147 (2011)[0pt] [3] H. Liu et al, IEEE EDL, 33, 546 (2012).
    03/2013;

Publication Stats

2k Citations
453.74 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