Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session P15: Semiconductors: Beyond CMOS Materials & Ballistic Transport |
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Sponsoring Units: FIAP Room: LACC 304C |
Wednesday, March 7, 2018 2:30PM - 2:42PM |
P15.00001: Out-of-plane Piezoelectricity and Ferroelectricity in Layered α-In2Se3 Nano-flakes Di Wu, Yu Zhou, Yihan Zhu, Yujin Cho, Qing He, Xiao Yang, Kevin Herrera, Zhaodong Chu, Yu Han, Michael Downer, Hailin Peng, Keji Lai Piezoelectric and ferroelectric properties in the two dimensional (2D) limit are nontrivial and they are highly desired for nanoelectronic, electromechanical, and optoelectronic applications. Here we present the experimental observation of out-of-plane piezoelectricity and ferroelectricity in van der Waals layered α-In2Se3 nano-flakes. The non-centrosymmetric R3m symmetry of the α-In2Se3 samples is confirmed by scanning transmission electron microscopy, second-harmonic generation, and Raman spectroscopy measurements. Ferroelectric domains with opposite polarizations are visualized by piezo-response force microscopy and the polarization can be switched for α-In2Se3 nano-flakes with thicknesses down to ~ 10 nm. The piezotronic effect is demonstrated in two-terminal devices, where the Schottky barrier can be modulated by the strain-induced piezopotential. Our work on polar α-In2Se3, one of the model 2D piezoelectrics and ferroelectrics with simple crystal structures, shows its great potential in nanoelectronic applications. |
Wednesday, March 7, 2018 2:42PM - 2:54PM |
P15.00002: Self-Propelling Active Particles & Self-Reconfiguring Assemblies from Remotely-Powered Thin Film Silicon Microdiodes Ugonna Ohiri, Koohee Han, Charles Shields, Talmage Tyler, Orlin Velev, Nan Jokerst Locally energized particles that are powered by external fields (e.g., electrical, magnetic, and optical) have formed the basis of emerging classes of reconfigurable active matter. We describe how millions of electrically- and magnetically-responsive silicon microparticles can be made to draw energy from applied external fields and actively propel, repel, rotate, and perform on-demand sequential assembly and disassembly. We show how a number of electric field-based effects such as electrohydrodynamic (EHD) flows, induced-charge electrophoresis, and dielectrophoresis, can selectively power this suite of particles. Microparticles subjected to a lower ac frequency (< 10 kHz) can propel and repel from each other when placed in proximate contact. At higher external field frequencies, the microparticles are attracted to each other due to induced dipolar interactions. We also briefly show that magnetic field-based effects such as magnetohydrodynamic (MHD) flows can induce additional functionalities to similarly designed particles. The result is the ability to achieve customized locomotion, interactions, reversible assembly, and synchronous rotational torque on demand that could enable advanced applications such as remotely powered microsensors and reconfigurable computational systems. |
Wednesday, March 7, 2018 2:54PM - 3:06PM |
P15.00003: Total Ionizing Dose Effects on the 1T-TaS2 Charge-Density-Wave Devices Guanxiong Liu, Enxia Zhang, Chundong Liang, Mathew Bloodgood, Tina Salguero, Alexander Balandin The voltage controlled charge-density-wave (CDW) phase transition in quasi-2D 1T-TaS2 offers a possibility of using the switching behavior of these states for electronic applications. We have recently demonstrated a frequency tunable oscillator based on an integrated graphene–h-BN–TaS2 device that is capable of operating at room temperature [1]. In this work, we evaluate the total ionizing dose (TID) effect on 1T-TaS2 CDW devices by examining the current-voltage characteristics under X-ray irradiation at doses up to 1 Mrad(SiO2). We find that the threshold voltage, VTH, for the abrupt resistance change shifts by only ~2%, the resistance of the CDW states changes by less than ~2 % (low resistive state) and ~6.5 % (high resistive state), and the voltage oscillations function well after the full irradiation sequence [2]. We attributed the radiation hardness of these CDW devices to the high carrier concentration and absence of the gate dielectric in the structure. [1] G. Liu, et al., Nature Nanotechnology, 11, 845 (2016); [2] G. Liu, et al., IEEE Electron Device Letters (accepted, 2017) 10.1109/LED.2017.2763597. |
Wednesday, March 7, 2018 3:06PM - 3:18PM |
P15.00004: Role of GaN surface Termination on Structural and Electronic Properties of 2D/GaN and Metal/2D/GaN Heterostructures Mahesh Neupane, DeCarlos Taylor, Dmitry Ruzmetov, Robert Burke, A. Birdwell, Andrew Herzing, Terrance O' Regan, Edward Byrd, Tony Ivanov Two-dimensional (2D) van-der-Waals (vdW) materials such as graphene and TMDCs have shown great promise in the field of nanoelectronics optoelectronic properties. In order to realize their full potential as channel materials in devices, these materials should form high-quality interfaces with bulk 3D substrates and metal contacts to minimize contact resistance and maximize current. Recently, we demonstrated the successful growth of a single layer (SL) of molybdenum disulfide (MoS2) on a GaN substrate through vdW epitaxy for vertical transistor [1]. Device characterization also revealed that the GaN-surface quality and polarity influenced both the structural and electronic properties of the 2D/3D heterostructures, mainly due to modulating vdW forces between the 2D layer and 3D substrate [2]. Motivated by these observations, here we present a first-principles study of structural and electronic properties of MoS2/GaN and metal/ MoS2/GaN heterostructures with Ga- and N-terminated GaN surfaces. We compare and contrast their material and electronic properties such as stacking order, vdW gap, work function, and Schottky barrier height (SBH). [1] Ruzmetov, D and et al., ACS Nano 2016, 10, 3580–3588. [2] O’Regan, T. P. Ruzmetov, D.; Neupane, M. R., and et al., APL. 2017, 111, 051602. |
Wednesday, March 7, 2018 3:18PM - 3:30PM |
P15.00005: Radio Frequency Transistors Using Aligned Semiconducting Carbon Nanotubes with Current-Gain Cutoff Frequency and Maximum Oscillation Frequency Simultaneously Greater than 70 GHz Yu Cao, Gerald Brady, Zhen Li, Sen Cong, Michael Arnold, Chongwu Zhou We report record radio frequency performance of carbon nanotube transistors based on combined use of a self-aligned T-shape gate structure, and well-aligned, high-semiconducting-purity, high-density polyfluorene-sorted semiconducting carbon nanotubes. These transistors show outstanding direct current performance with on-current density of 350 μA/μm, transconductance as high as 310 μS/μm, and superior current saturation with normalized output resistance greater than 100 kΩ*μm. These transistors create a record as carbon nanotube RF transistors that demonstrate both the current-gain cutoff frequency and the maximum oscillation frequency greater than 70 GHz. Furthermore, these transistors exhibit good linearity performance with 1 dB gain compression point of 14 dBm and input third-order intercept point of 22 dBm. Our study advances carbon nanotube RF electronics, which have the potential to be made flexible and may find broad applications for signal amplification, wireless communication, and wearable/flexible electronics. |
Wednesday, March 7, 2018 3:30PM - 3:42PM |
P15.00006: Determining the Intrinsic and Extrinsic Properties of Black Phosphorus by AC Conductance and Capacitance Techniques Jialun Liu, Wenjuan Zhu, Yujie Zhou Most studies on the electrical properties of the black phosphorus (BP) are based on direct-current (DC) measurements. We study BP capacitors by probing the intrinsic and extrinsic material properties of BP by capacitance and AC conductance measurements. We determine the transport band gap of 50 nm BP as 0.31 eV based on the temperature dependence of the transition frequencies. By modeling, doping concentration of the BP as 3 x 1018 in a BP/BN capacitor and as 1.8 x 1018 in a BP/Al2O3 capacitor are extracted, suggesting Al2O3 deposited by atomic layer deposition (ALD) introduces n-type doping (counter-doping) to the originally p-type doped BP crystals. The interface states in BP/Al2O3 capacitors from AC conductance method exhibits a U-shaped energy distribution with the minimum located at the midgap. The interface trap density in the BP/BN capacitor is around one order lower than that in the BP/Al2O3 capacitor. We also propose to fabricate BP MOSFET and extracted barrier heights hence bandgap by Id-Vg characteristics and make a comparison to Eg above. This investigation of properties of BP will provide important information for designing and fabricating future electronic/photonic devices based on this material. |
Wednesday, March 7, 2018 3:42PM - 3:54PM |
P15.00007: Chlorine Terminated Si (100) Studied by Low-Temperature Scanning Tunneling Microscopy Michael Dreyer, Wan-Ting Liao, Robert Butera We used low temperature scanning tunneling microscopy (STM) operating at 4.2 K to study the chlorine terminated surface of a silicon (100) phosphorous doped sample. The goal of this study is to gain insight into the electronic structure of the adsorbed Cl as well as into the Cl desorption mechanism. Furthermore, Cl, similar to a hydrogen passivation layer, reduces band pinning at the surface so that the tip induced quantum dot and its interaction with dopants can be observed. First, the native oxides of silicon were removed by direct current heating in an attached UHV system. Subsequently, the samples were exposed to Cl using a home build source. Depending on the exposure time, the samples could be partially or fully covered by Cl. The samples were then transferred into the low temperature STM to acquire topographic and spectroscopic data. |
Wednesday, March 7, 2018 3:54PM - 4:06PM |
P15.00008: Computational study of quantum electron transport in ohmic edge contacts between two-dimensional materials Wushi Dong, Peter Littlewood In-plane edge contacts can achieve lower contact resistance due to stronger orbital hybridization compared to conventional van der Waals top contacts. However, the quantitive understanding of the electron transport properties in the edge contact is still lacking. In this work, we present full-band atomistic quantum transport simulations of the Graphene/MoS2 edge contact. A self-consistent calculation is done by simultaneously solving the Keldysh Non-equilibrium Green’s Functions formalism for the charge density and the Poisson equation for the electrostatic potential. The tight-binding parameters extracted from the Maximally-Localized Wannier Functions enable us to model such realistic structures at first-principle accuracy and minimal computational cost. We successfully reproduced the ohmic I-V characteristics as measured in the experiments. Our study could have broad implications in the design and fabrication of purely 2D metal-semiconductor junction for realizing atomically thin electronics with low-resistance contacts. |
Wednesday, March 7, 2018 4:06PM - 4:18PM |
P15.00009: Non-universal transmission phase behaviour of a large quantum dot Hermann Edlbauer, Shintaro Takada, Grégoire Roussely, Michihisa Yamamoto, Seigo Tarucha, Arne Ludwig, Andreas D. Wieck, Tristan Meunier, Christopher Bäuerle The electron wave function experiences a phase modification at coherent transmission through a quantum dot. This transmission phase undergoes a characteristic shift of π when scanning through a Coulomb blockade resonance. Between successive resonances either a transmission phase lapse of π or a phase plateau is theoretically expected to occur depending on the parity of quantum dot states. Despite considerable experimental effort, this transmission phase behaviour has remained elusive for a large quantum dot1. Here we report on transmission phase measurements across such a large quantum dot hosting hundreds of electrons. Scanning the transmission phase along fourteen successive resonances with an original two-path interferometer, we observe both phase lapses and plateaus. We demonstrate that quantum dot deformation alters the sequence of phase lapses and plateaus via parity modifications of the involved quantum dot states2. Our findings set a milestone towards a comprehensive understanding of the transmission phase of quantum dots. |
Wednesday, March 7, 2018 4:18PM - 4:30PM |
P15.00010: Unveiling the bosonic nature in a ultrafast single electron pulse Grégoire Roussely, Everton Arrighi, giorgos georgiou, Shintaro Takada, Martin Schalk, Arne Ludwig, Andreas D. Wieck, Pacôme Armagnat, Thomas Kloss, Xavier Waintal, Tristan Meunier, Christopher Bäuerle Quantum dynamics are very sensitive to dimensionality. While two-dimensional electronic systems form Fermi liquids, one-dimensional systems – Luttinger liquids – are described by purely bosonic excitations even though they are initially made of fermions. With the advent of coherent single electron sources, the quantum dynamics of such a liquid are now accessible at the single electron level. Here, we report on time-of-flight measurements of ultrashort single electron charge pulses injected into a quasi one-dimensional quantum conductor. We change the confinement potential from the one-dimensional Luttinger liquid limit to the multichannel Fermi liquid. Our measurements show that the plasmon velocity can be varied over almost an order of magnitude, even in the quantum regime where the pulses carry one or less electrons. These results are in quantitative agreement with a parameter-free theory and demonstrate a powerful new probe for directly investigating real-time dynamics of fractionalisation phenomena in low-dimensional conductor. |
Wednesday, March 7, 2018 4:30PM - 4:42PM |
P15.00011: Coherent manipulation of a single electron surfing on a sound wave Shintaro Takada, Hermann Edlbauer, Arne Ludwig, Andreas D. Wieck, Tristan Meunier, Christopher Bäuerle Surface acoustic waves (SAW) provide a promising platform to realize quantum optics experiments with electrons at the single particle level. Earlier single shot experiments have shown SAW-assisted electron transport between spatially separated quantum dots over a distance of 4 µm with an efficiency of about 92 % [1]. Here we go an important step further. We couple two quantum channels by a tunnel barrier along a region of 2 µm. At the ends of each channel respectively a quantum dot is placed serving as single electron source and detector. We demonstrate single electron transport over a distance of 22 µm with extremely high efficiency above 99 %. Changing the energy detuning in the coupling region we can partition the electron on-demand into two paths. By gradually changing the barrier height we additionally observe tunnel oscillations of the probability that the electron ends up at the upper or the lower detector quantum dot. This finding demonstrates coherent manipulation of the electron quantum state on the fly. Our results pave the way for the implementation of a solid state flying qubit having high relevance in fundamental research and quantum information technology. |
Wednesday, March 7, 2018 4:42PM - 4:54PM |
P15.00012: Kinetic Theory of the Dyakonov-Shur Instability Christian Mendl, Andrew Lucas One of the most promising routes to the spontaneous generation of terahertz radiation is the Dyakonov-Shur instability of a two-dimensional electron gas [Dyakonov and Shur, Phys. Rev. Lett. 71, 2465 (1993)]. This instability arises from a non-standard, but experimentally achievable choice of boundary conditions on the electron gas, coupled to a uniform background current flow. Despite much circumstantial evidence for this instability, a clean experimental realization has proven to be difficult, most likely since the instability was implicitly deep in a hydrodynamic regime, where electrons collide with each other at a rate 1/τee much larger than Umklapp or phonon/impurity collisions. In this talk, we will investigate the fate of the instability across the hydrodynamic-to-ballistic transition via semiclassical kinetic theory. While the instability disappears in an intermediate regime of τee, it reappears in the ballistic limit τee → ∞ for certain boundary conditions. |
Wednesday, March 7, 2018 4:54PM - 5:06PM |
P15.00013: Tailoring ballistic injection Toussaint Sebastien, Boris Brun-Barrière, Sebastien Faniel, Ludovic Desplanque, Xavier Wallart, Vincent Bayot, Benoit Hackens Efficient electron injection into nanoscale devices is difficult to experimentally characterize at the local scale. We discuss here how little modifications of the electrostatic potential landscape in the vicinity of a nanodevice injection leads can drastically enhance electron transmission, by tuning semi-classical trajectories and directly re-orienting charge flow in the desired paths. In this context, quantum rings (QRs) appear as interesting geometries since, in a semiclassical view, most electrons bounce against the hard-wall potential of the central QR antidot directly after injection. We found that a local partial depletion of the QR close to this hard-wall can counter-intuitively ease ballistic electron flow. On the contrary, local charge accumulation can focus the flow on the hard wall potential and increase back-scattering. Simulating current density distributions in the ring gives insights on these peculiar transmission conditions. Using a voltage-polarised scanning gate to tune in situ the ballistic electron flow in a QR patterned from a high mobility 2D electron system, we find a remarkable direct experimental confirmation of this particular phenomenology. |
Wednesday, March 7, 2018 5:06PM - 5:18PM |
P15.00014: Spin-orbit interactions and the origins of the huge anisotropy of in-plane g-factors in 1D holes in GaAs quantum point contacts Alex Hamilton, Ashwin Srinivasan, Dima Miserev, O. Tkachenko, V. A., I. Farrer, David Ritchie, Oleg Sushkov Holes in 2D and 1D GaAs systems have a very strong spin-orbit interaction due to the J=3/2 nature of the heavy holes. It has been known for over a decade that the in-plane hole g factors in GaAs quantum point contacts has a very strong dependence on the orientation of the magnetic field with respect to the electric current. However, despite numerous observations of this effect by multiple groups, the origins of this anistropy have remained a mystery. Here we resolve this problem. We present systematic experimental studies to disentangle different mechanisms contributing to the g-factor anisotropy. Theoretical analysis shows that there is a new mechanism for the anisotropy related to the existence of an additional B+k-4σ+ effective Zeeman interaction for holes, which is kinematically different from the standard Zeeman term B-k-2σ+ considered in previous works. |
Wednesday, March 7, 2018 5:18PM - 5:30PM |
P15.00015: Imaging the zig-zag Wigner crystals in confinement-tunable quantum wires Sheng-Chin Ho, Heng-Jian Chang, Chia-Hua Chang, Shun-Tsung Lo, Graham Creeth, Sanjeev Kumar, Michael Pepper, Ian Farrer, David Ritchie, Jonathan Griffiths, Geraint Jones, Tse-Ming Chen Wigner crystal has so far only been evident in two-dimensional electron systems. For the more interacting one-dimensional (1D) systems, such a Wigner electron lattice has proven very challenging to probe experimentally, and the precise nature of it has remained elusive. Theory suggests that the 1D Wigner crystal will transit to a zig-zag phase when the confinement weakens. Here we utilize the magnetic focusing technique to probe the formation of a zig-zag Wigner lattice, in which the transverse distribution of electrons in a quantum wire reveals itself in the magnetic focusing spectrum. Trasition from a 1D Wigner to zig-zag phase, manifested in the evolution from a focusing peak singlet to doublet, is present when the wire confinement potential continuously weakens. The spin properties of the Wigner electron lattices can also be studied using our magnetic focusing technique. We show that a ferromagnetic phase can occur when the zig-zag Wigner crystal is formed. |
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