Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session F52: Ballistic Transport in Semiconductor Devices |
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Sponsoring Units: FIAP Chair: Wei-Cheng Lee, Binghamton University Room: Room 308 |
Tuesday, March 7, 2023 8:00AM - 8:12AM |
F52.00001: Thermal-driven neuromorphic computing devices Hsin-Ju Chen, Chih-Chieh Chiang, Chun-Yun Cheng, Danru Qu, Ssu-Yen Huang Neuromorphic computing devices which emulate biological neural networks are vital in realizing artificial intelligence for information processing and decision-making. To date, various types of neuromorphic computing devices with multi-level resistance states have been developed, including the memristor-based devices caused by ion diffusion, the phase transition-based devices caused by threshold switching and progressive crystallization/amorphization, the spintronics-based devices caused by magnetic domain switching, etc. However, these devices may face critical challenges such as instability in integrated circuits and non-linearity in synaptic weight change. To overcome these difficulties, we present a thermal-driven multi-layer-multi-terminal neuromorphic computing device with a performance of high endurance, high reliability, and high linearity. We use a pulse current sequence to variate resistance by the asymmetric Joule heating in this device and demonstrate a wide range of synaptic functions, including potentiation, depression, and both anti-symmetric and symmetric spike-timing-dependent plasticity. Furthermore, our thermal-driven asymmetric Joule heating devices with multiple functionalities open an energy-efficient platform for future neuromorphic computing devices and artificial intelligence. |
Tuesday, March 7, 2023 8:12AM - 8:24AM |
F52.00002: Nanoscale Field-Emission Frequency Mixer Lucia De Rose, Changsoon Choi, Axel Scherer In the first half of the twentieth century, all electronic devices used vacuum tubes in their circuits. However, the emergence of the transistor and later integrated circuit (IC) technology, quickly replaced the bulky vacuum tubes in almost all areas. Solid-state electronics (SSE) devices were less fragile, smaller, more energy efficient, and above all, able to be mass-produced. Thus, vacuum devices were displaced to a handful of niche applications such as microwave power amplifiers, and high temperature and radiation environments. Yet, despite the apparent pushover of SSE, vacuum technology did not perish. Paradoxically, the same fabrication and processing tools developed to shrink the size of solid-state ICs also enabled the miniaturization of vacuum technology giving rise to the field of vacuum nanoelectronics. By reducing their physical dimensions, vacuum devices can leverage some of the distinct inherent advantages including ballistic electron transport due to the lack of lattice scattering as well as resilience in harsh environments. The re-emergence of this technology is opportune as SSE seem to be approaching their technical limitations, as heat dissipation and quantum effects are arising due to the steady shrinkage. |
Tuesday, March 7, 2023 8:24AM - 8:36AM |
F52.00003: Nonreciprocal charge current in a bulk Rashba semiconductor above the band crossing point Aniruddha Pan, D. C Marinescu We calculate the nonreciprocal charge current in a bulk semiconductor with Rashba spin-orbit coupling subjected to crossed electric and magnetic fields. By using a second-order distribution function derived in a perturbative approach that considers the change in the local electron energy induced by the electric field [Physical Review B, 99(24), 245204], we find that, in contrast with previous theoretical estimates, a charge current proportional to the applied magnetic field exists for all values of the chemical potential, above or below the band crossing point (BCP), the energy where the two chiral conduction bands intersect. The persistence of the quadratic electric current across the BCP is a consequence of the chiral dependence of the relaxation times, an effect neglected before. |
Tuesday, March 7, 2023 8:36AM - 8:48AM |
F52.00004: Quantum point contacts on a GeSn/Ge heterostructure Tsung-Ying Li, Yu-Jui Wu, Hung-Yu Tsao, Min-Jui Lin, Chia-You Liu, Chia-Tse Tai, Jiun-Yun Li GeSn is a promising material for spintronics and quantum technology owing to its strong spin-orbit coupling (SOC). In this work, we present quantized conductance in a quantum point contact (QPC) on a Ge0.94Sn0.06/Ge heterostructure for the first time. The heterostructure was grown by reduce-pressure chemical vapor deposition. Secondary ion mass spectroscopy (SIMS) was used to characterize the Sn fractions in the GeSn alloys. Transmission electron microscopy (TEM) images show high-quality crystallinity of the Ge/GeSn heterostructures. We characterized carrier transport in the GeSn/Ge heterostructure by performing Hall measurements at 1.8 K with the highest mobility of ~ 30,000 cm/V-s. We observed clear quantum Hall plateaus and Shubnikov-de Haas oscillations at large magnetic fields. Under a large magnetic field of 3 T, GeSn-based QPCs show quantized conductance of e2/h, which is attributed to the lift-up of spin degeneracy by Zeeman effects. Under a zero magnetic field, this e2/h quantized plateau can still be observed, which might be attributed to strong SOC or carrier interactions. |
Tuesday, March 7, 2023 8:48AM - 9:00AM |
F52.00005: Single-electron source with a quantum Hall edge state Myung-Ho Bae, Sung Un Cho, Wanki Park, Bum-Kyu Kim, H.-S. Sim Electron quantum optics has been developed based on the wave nature of electrons in various solid-state devices such as GaAs/AlGaAs and graphene. The coherent manipulation of individual electrons in a single electron level could lead another qubit platform, corresponding to the path qubit with single photons. To the end, a coherent on-demand single-electron source is necessary. In this talk, I will introduce a single-electron source based on a quantum dot with a finite changing energy and quantum Hall edge state. When we drove the quantum dot by an AC gate voltage, it absorbs electrons, leaving a hole in the edge channel and successively emits electrons into the same channel with the modulation of the AC voltage. With an energy barrier in the edge channel, we successfully separated the emitted electrons and holes, leading to a rectified single-electron current satisfying a relation of I = −ef, where e is the elementary charge and f is the frequency of the AC drive. In the energy spectroscopy with the energy barrier, we observed that the energy distribution of the single electrons showed only ~5 meV at a 40 meV-energy level, contrary to a ~23 meV broadening at the same level for a conventional tunable-barrier quantum dot. Thus, we believe that our newly developed single-electron source could be useful to find a coherence of electrons at a few-tens meV level. |
Tuesday, March 7, 2023 9:00AM - 9:12AM |
F52.00006: An investigation of the disorder potential of quantum point contacts via scanning gate microscopy and machine learning Carlo R daCunha, David K Ferry, Nobuyuki Aoki Scanning Gate Microscopy (SGM) is one of the scanning probe techniques where a charged tip perturbs an electron sea while changes in conductance are concomitantly measured. Under very strict conditions such as a sufficiently weak perturbation caused by a delta-shaped potential, the SGM signal shows some correspondence with the local density of states of the device. These conditions, however, are typically difficult to be met and the usefulness of the technique is often questionable. Here, however, we show that it is possible to extract usefull information from SGM measurements if one considers it an inverse problem in quantum mechanics and uses machine learning tools to solve it. |
Tuesday, March 7, 2023 9:12AM - 9:24AM |
F52.00007: Manipulating spin dynamics in one-dimension using transverse magnetic focusing. Harry Z Smith, Patrick See, Ian Farrer, David A Ritchie, Sanjeev Kumar Transport in one-dimensional (1D) nanostructures in particular the impact of exchange-correlation terms on the spin dynamics has become an increasingly important area of research. In this regard, using transverse magnetic focusing (TMF), we may explore the spatial separation of spins as a function of splitting of periodic focusing peaks [1]. This separation is highly dependent on a difference in kF of the spin-states and becomes tuneable with charge carrier density and out of plane asymmetry due to spin orbit coupling [2]. In the present work we aim to leverage high quality GaAs/AlGaAs heterostructures to define longer, and wider 1D quantum wires to form injector and detector in the TMF configuration. However, the relatively weaker spin orbit coupling in this system, compared to others with reported peak splitting [2], requires new measures for inducing different kF of the spin-states, which may result in of improvement in peak splitting. Recently we achieved this by incorporating a top-gate over the focusing path. This top gate induced splitting in peaks was found to vary with the application of in-plane magnetic field, suggesting the effect is spin related. Results will be discussed with reference to existing theories around spin orbit coupling, exchange interactions as well as the device geometries. |
Tuesday, March 7, 2023 9:24AM - 9:36AM |
F52.00008: Spatially confined fractional quantum states in one-dimension Sanjeev Kumar, Michael Pepper, Ian Farrer, David A Ritchie, H Montagu Recently, the quantized conductance in asymmetrically confined quasi-one-dimensional quantum wires formed in GaAs/AlGaAs based heterostructures was shown to appear at fractional values of e2/h in the absence of a quantising magnetic field [1-3]. In this work, we show that when an electrostatically defined 1D quantum wire was spatially relaxed by shallowing the confinement potential, the interacting 1D electrons formed a zigzag resulting in fractional conductance states at 1 and 2/5. Additional fractional states appeared at 2/5 and 2/7 on applying a large in-plane magnetic field. The magnetic field, in addition to electron-electron interaction, may result in antiphase correlated motion resulting in a more complex pattern of cyclic motion [2]. Temperature dependence of 2/5 state shows the fractional state was stable until 300 mK before starting to smear out. |
Tuesday, March 7, 2023 9:36AM - 9:48AM |
F52.00009: Length estimation of a finite length quantum wire from finite size effects Henok Weldeyesus, Taras Patlatiuk, Christian P Scheller, Gilad Barak, Amir Yacoby, Loren N Pfeiffer, Ken West, Dominik M Zumbuhl When tunneling between two parallel quantum wires the current is proportional to |M(k)|2, where M(k) is the Fourier-transform of the product of the participating wave functions in the two wires. Since the wave-vectors in both wires are generally different, M(k) will be strongly peaked at k±=k1±k2. Here k1,2 are the Fermi wave-vector in wires 1 or 2. |
Tuesday, March 7, 2023 9:48AM - 10:00AM |
F52.00010: Engineering long ballistic single mode electrostatically defined quantum wires for future detection of Majorana zero modes Krittika Kumar, Karina L Hudson, Leah Tom, Benjamin Ramsay, Yonatan Ashlea Alava, Qingwen Wang, Yik Kheng Lee, Jackson S Smith, Jared Cole, Ian Farrer, David A Ritchie, Mark Friesen, Susan N Coppersmith, Alexander R Hamilton A key challenge to realising and detecting Majorana Zero Modes is the need to form low disorder, single mode 1D systems: If the quantum wire is too short the Majorana modes will annihilate each other. In transport measurements a short 1D wire length also leads to a high energy uncertainty, which masks the signature of the spin-gap (a prerequisite for Majorana Zero Modes). Split gate devices on high mobility 2D systems are a potential ultra-low disorder alternative to physically etched or self-assembled nanowires for probing Majorana Zero Modes. However it is non-trivial to create long single mode wires electrostatically as even in the absence of disorder the length of the single mode region is usually much shorter than the physical gate dimensions. |
Tuesday, March 7, 2023 10:00AM - 10:12AM |
F52.00011: In situ epitaxial aluminium gates in ultra-shallow GaAs/AlxGa1-xAs heterostructures for low noise quantum point contacts Yonatan Ashlea Alava, Daisy Q Wang, Chong Chen, David A Ritchie, Arne Ludwig, Julian Ritzmann, Andreas D Wieck, Oleh Klochan, Alex R Hamilton The mobility of the two-dimensional electron gas (2DEG) in shallow GaAs/AlxGa1−xAs heterostructures is strongly suppressed by unwanted Coulomb scattering from surface charge, likely located in native surface oxides that form after the wafer is removed from the crystal growth system. In this work, we show that this native surface oxide can be eliminated by growing an epitaxial aluminium gate before removing the wafer from the growth chamber. We examine the influence of aluminium gate thickness and the use of different semiconductor wetting layers on the semiconductor-aluminium interface and correlate this with the electron mobility. Transmission electron microscope (TEM) characterisation of the different wafers shows the in-situ epitaxial aluminium is crystalline, with a near-perfect semiconductor-aluminium interface that is oxide-free. The electron mobility is found to strongly depend on aluminium thickness, as well as the wetting layer the Al is grown on. Low-temperature transport measurements show the in-situ epitaxial aluminium gate design greatly reduces surface charge scattering, with up to an 2.5× increase in mobility compared to a device with an ex-situ gate design. We demonstrate the use of epitaxial gates for quantum devices making a quantum point contact which shows robust and reproducible 1D conductance steps. Noise measurements reveal a reduction in charge noise of over an order of magnitude with respect to previous work, despite the 35-nm channel. |
Tuesday, March 7, 2023 10:12AM - 10:24AM |
F52.00012: Observation of oscillating g-factor anisotropy arising from strong crystal lattice anisotropy in GaAs spin-3/2 hole quantum point contacts Karina L Hudson, Ashwin Srinivasan, Dmitry Miserev, Qingwen Wang, Oleh Klochan, Oleg P Sushkov, Ian Farrer, David A Ritchie, Alex R Hamilton Many modern spin-based devices rely on the spin-orbit interaction, which is highly sensitive to the host semiconductor heterostructure and varies substantially depending on crystal direction, crystal asymmetry (Dresselhaus), and quantum confinement asymmetry (Rashba). One-dimensional quantum point contacts are a powerful tool to probe both energy and directional dependence of spin-orbit interaction through the effect on the hole g-factor. In this work we investigate the role of cubic crystal asymmetry in driving an oscillation in the in-plane hole g-factor anisotropy when the quantum point contact is rotated with respect to the crystal axes, and we are able to separate contributions to the Zeeman Hamiltonian arising from Rashba and cubic crystal asymmetry spin-orbit interactions. The in-plane g-factor is found to be extremely sensitive to the orientation of the quantum point contact, changing by a factor of 5 when rotated by 45°. This exceptionally strong crystal lattice anisotropy of the in-plane Zeeman splitting cannot be explained within axially symmetric theoretical models. Theoretical modelling based on the combined Luttinger, Rashba and Dresselhaus Hamiltonians that we use here reveals new spin-orbit contributions to the in-plane hole g-factor and provides an excellent agreement with our experimental data. |
Tuesday, March 7, 2023 10:24AM - 10:36AM |
F52.00013: Measurement of thickness dependent anisotropic thermal conductivities in highly anisotropic semiconductors Shany Mary Oommen, Simone Pisana Semiconductors with highly anisotropic thermal conductivity are a substrate in device designs with highly efficient heat dissipation. In this study, we measured the anisotropic thermal conductivities as a function of thickness in various highly anisotropic semiconductors using time domain thermoreflectance technique (graphite, h-BN and MoS2). Our results show that in graphite, as the thickness of the flake reduces both in-plane and out-of-plane thermal conductivities deviates significantly from the bulk value due to the presence of phonons with large mean free path; On the other hand, due to the presence of phonons with shorter mean free path, MoS2 flakes with thicknesses similar to graphite showed thermal conductivities comparable to its bulk value. When the thickness of the flake is reduced and is comparable with the mean free path of the phonons, heat transport is not diffusive anymore and becomes quasi-ballistic. Understanding the thermal anisotropy in two-dimensional materials as a function of their thickness has relevant applications in various fields such as microelectronics, thermoelectric applications, etc. |
Tuesday, March 7, 2023 10:36AM - 10:48AM |
F52.00014: Machine Learning and Electronic Phases and Band Structures of Thin Film Narrow-Gap and Semimetallic Electronic Materials for New Chips and New Energy Shuang Tang, Michael Taber The current semiconducting and computing materials system is mostly based on thin films. When exploring the next generation systems for electronics, researchers have found that narrow-band-gap materials are of great interest, mainly because of their ultra-high mobility and small power consumption. When narrow-band-gap materials are made into thin films, the quantum confinement effect is obviously higher than in wide-band-gap semiconductors. |
Tuesday, March 7, 2023 10:48AM - 11:00AM |
F52.00015: Mechanism of the Resistivity Switching Induced by Joule Heating in Crystalline NbO2 Samuel W Olin, Wei-Cheng Lee, Sarah Mohammed, Louis F Piper The memristive electrical transport properties in NbO2 are of great interest due to their promising application to neuromorphic computation. Much is still unknown about this material, in particular whether its metal-to-insulator transition (MIT) originates from the Peierls or the Mott mechanism. We use both measurement and first-principles calculation to develop a thermodynamic model of a second order Peierls MIT in NbO2 driven by Joule heating under bias voltage. The electrical conductivity is fit via temperature dependent energy gap, in accordance with weakening dimerization. The Joule heating equation is solved, and it is found that the system is unable to host a steady-state solution above a certain threshold bias. Finally, the Ginzburg-Landau theory is used to image the weakening of Nb-Nb dimers under heating. The resistivity switch can be understood by emergence of dimer-free conducting regions. Hence, we provide strong evidence of a domain wall model of NbO2 memristance. |
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