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The 20th International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures (EDISON 20) was held at the Hyatt Regency Hotel and Conference Center in downtown Buffalo, New York, USA from July 17–21, 2017. The meeting serves as the premier forum for researchers working on the study of nonequilibrium phenomena in semiconductors, from all parts of the globe, and was organized locally by faculty at the University at Buffalo and the University of Rochester.

EDISON is an international conference series with biennial meetings that cover recent progress in the field of electron dynamics in solid-state materials and devices. Initially established with the title Hot Carriers in Semiconductors (HCIS), the first meeting took place in Modena, Italy in 1973. The name was changed to International Conference on Nonequilibrium Carrier Dynamics in Semiconductors at the 1997 Berlin meeting, and again at the 2009 meeting in Montpellier to the current form. Since then, EDISON conferences have been held in Santa Barbara, USA (2011); Matsue, Japan (2013); Salamanca, Spain (2015); and Buffalo, USA (2017).

The EDISON 20 program included 12 invited talks, 50 oral contributions, 116 accepted abstracts, and one special seminar. In total, 152 participants from 22 countries gathered to share and exchange ideas and recent results. Approximately 45% of the participants were from North America, 30% from Europe, and 25% from the Asia Pacific region. Fully 30% of the participants were students, and there was a very good balance between experimental and theoretical approaches. Topics with the most contributions were: Electronic and optical properties of graphene and other 2D materials; Nonequilibrium carrier transport; and Terahertz phenomena in semiconductor materials and devices.

I thank all the members of the Program Committee and the International Advisory Committee for their valuable input, as well as Professor Jonathan Bird and Alex Desha for their many hours devoted to organizing a successful EDISON conference. Also critical to the success of the conference is financial support, so I thank the School of Engineering and Applied Sciences, the Vice President for Research and Economic Development, the Department of Physics, and the Department of Electrical Engineering at the University at Buffalo, as well as the U.S. Department of Energy, Kurt J. Lesker Company, and the Hajim School of Engineering & Applied Sciences at the University of Rochester for their sponsorship of EDISON 20. Finally, I thank all the scientists who contributed to the preparation and peer-review of these proceedings.

Erik Einarsson, Editor

EDISON 20 Publications Chair

University at Buffalo

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

We present our studies on fabrication and electrical and optical characterization of semiconducting asymmetric nanochannel diodes (ANCDs), focusing mainly on the temperature dependence of their current–voltage (I–V) characteristics in the range from room temperature to 77 K. These measurements enable us to elucidate the electron transport mechanism in a nanochannel. Our test devices were fabricated in a GaAs/AlGaAs heterostructure with a two-dimensional electron gas layer and were patterned using electron-beam lithography. The 250-nm-wide, 70-nm-deep trenches that define the nanochannel were ion-beam etched using the photoresist as a mask, so the resulting nanostructure consisted of approximately ten ANCDs connected in parallel with 2-µm-long, 230-nm-wide nanochannels. The ANCD I–V curves collected in the dark exhibited nonlinear, diode-type behavior at all tested temperatures. Their forward-biased regions were fitted to the classical diode equation with a thermionic barrier, with the ideality factor n and the saturation current as fitting parameters. We have obtained very good fits, but with n as large as ∼50, suggesting that there must be a substantial voltage drop likely at the contact pads. The thermionic energy barrier was determined to be 56 meV at high temperatures. We have also observed that under optical illumination our ANCDs at low temperatures exhibited, at low illumination powers, a very strong photoresponse enhancement that exceeded that at room temperature. At 78 K, the responsivity was of the order of 10⁴ A/W at the nW-level light excitation.

This work presents results of terahertz time-domain spectroscopy (THz-TDS) investigations of two types of polymer-based nanocomposites, consisting of bulk samples of graphene nanoflakes embedded in a polymer matrix and thin films where single-walled carbon nanotubes (SWCNTs) with a chiral index (7,5) were wrapped in single strains of a polymer. Our THz-TDS setup is a room-temperature system with a frequency range of 0.1 to 3.5 THz, based on photoconductive switches as both the emitter and detector, excited by 100-fs-wide optical pulses. We have studied THz spectra of both types of samples and compared them to the ones obtained for the pure polymer reference specimens and fitted the experimental complex conductivity data to the Drude–Smith model. The Drude–Smith model fits our data well, demonstrating that graphene nanoflakes and SWCNTs, exhibit highly localized intra grain/tube electron backscattering with a femtosecond relaxation time.

We report on experimental and theoretical studies of nanoscale gate-lengths strained Silicon MODFETs as room temperature non resonant detectors. Devices were excited at room temperature by an electronic source at 150 and 300 GHz to characterize their sub-THz response. The maximum of the photovoltaic response was obtained when the FET gate was biased at a value close to the threshold voltage. Simulations based on a bi-dimensional hydrodynamic model for the charge transport coupled to a Poisson equation solver were performed by using Synopsys TCAD. A charge boundary condition for the floating drain contact was implemented to obtain the photovoltaic response. Results from numerical simulations are in agreement with experimental ones. To understand the coupling between terahertz radiation and devices, the devices were rotated at different angles under excitation at both sub-terahertz frequencies and their response measured. Both NEP (Noise Equivalent Power) and Responsivity were calculated from measurements. To demonstrate their utility, devices were used as sensors in a terahertz imaging system for inspection of hidden objects at both frequencies.

We have performed nonequilibrium Green function simulations on the vertical transport characteristics in multilayer graphene nanoribbons sandwiched between two graphene contact layers with varying the inter-layer coupling strength β. We find that the integrated transmission function thorough the top (or bottom) layer is hardly affected by β when the incident energy is close to the Dirac point. The β-insensitive energy window becomes narrower as the channel length increases.

The transport scaling limits of Ovonic devices are studied by means of a numerical solution of a time- and space-dependent transport model based on a set of equations that provide a good physical grasp of the microscopic process in hand. The predictivity of the approach has been confirmed through the comparison with recent experimental results where the parasitic effects have been reduced by the use of top-technology measuring equipments. The present analysis is performed for the AgInSbTe chalcogenide, since this material exhibits a steep threshold-switching dynamics which makes it promising for high-speed, non-volatile memory applications.

The optically coupled exciton states have been investigated in terms of power dependent photoluminescence at the coupled GaAs quantum dots, which were laterally coupled along the [1$\bar{1}$0] direction. The power dependent photoluminescence results are compared with two different excitation directions which are parallel to the direction of [1$\bar{1}$0] and [110]. In coupled direction along the [1$\bar{1}$0] direction, the power dependent redshift and coupled biexciton are observed, a fact that may be attributed to optical couplings via dipole-dipole interactions. Also, the redshift of excitons was manifested based on theoretical model.

The phonon dispersions and their related properties are computed in polytype materials by using a semi-empirical approach called adiabatic bond charge model. Both hexagonal 2H and cubic 3C phases of Silicon and Germanium are investigated in terms of heat capacity, Raman shift and sound velocities for each phonon branch in all main directions.

The lateral interdot coupling is investigated in high density (∼10 cm⁻² ) self-assembled InAs quantum dots (QDs) grown on an InP substrate. Two types of structures are selected for this study, in which QDs are embedded into an InAlAs matrix, forming nearly twice stronger confinement for an electron and a hole than expected for an InAlGaAs counterpart. Resonantly injected low carrier population in these families of QDs gives very different spectral and temporal response in the temperature range of 5-30 K. While InAs/InAlGaAs QDs show monotonic temperature quench of photoluminescence (PL), the process seems to be ineffective in the family of InAs/InAlAs dots. Moreover, the PL decay traces for InAs/InAlGaAs QDs reveal a two-exponential decay as compared to a mono-exponential one observed for InAs/InAlAs dots. While a short decay component of ≤1.9 ns has been attributed to recombination of an electron-hole pair confined in the dot, the long one of >2.4 ns, observed exclusively for InAs/InGaAlAs QDs, is attributed to recombination of spatially separated electron-hole pairs formed due to carrier exchange between adjacent dots.

A quantum dot is created within a suspended nanobridge containing a two-dimensional electron gas. The electron current through this dot exhibits well-pronounced Coulomb blockade oscillations. When surface acoustic waves (SAW) are driven through the nanobridge, Coulomb blockade peaks are shifted. To explain this feature, we derive the expressions for the quantum dot level populations and electron currents through these levels and show that SAW-induced Rabi oscillations lead to the observed phenomenology.

An extended hydrodynamic model self-consistently coupled to the 2D Schrödinger and 3D Poisson equations is introduced, to describe charge transport in Silicon Nanowires. It is been formulated by taking the moments of the multisubband Boltzmann equation, and the closure relations for the fluxes and production terms have been obtained by means of the Maximum Entropy Principle. The low-field mobility for a Gate-All-Around in a SiNW transistor has been evaluated.

The Wigner transport equation is solved by Direct Simulation Monte Carlo, based on the generation and annihilation of signed particles. In this framework, stochastic algorithms are derived using the theory of pure jump processes with a general state space. Numerical experiments on benchmark test cases are shown.

We theoretically study the coherent dynamics of Dirac fermions at the surface of a 3D topological insulator (Bi₂Se₃) in the field of an ultrafast laser pulse. In the presence of the ultrafast pulse, which has a femtosecond time scale that is less than the characteristic electron scattering time in these materials, the electron dynamics is coherent. Because of the gapless dispersion relation, the electrons dynamics is highly irreversible, which is dramatically different from dielectrics (fused silica, quartz, and sapphire). Due to irreversibility, finite conduction band population does exist after the pulse ends. Within two-band k.p Hamiltonian, which includes cubic momentum hexagonal warping terms, the residual conduction band (RCB) population in the reciprocal space is highly anisotropic. The distribution of RCB population in the reciprocal space strongly depends on the polarization of the ultrafast laser pulse.

Electron transport and drain current noise in the wurtzite GaN MOSFET have been studied by Monte Carlo particle simulation which simultaneously solves the Boltzmann transport and pseudo-2D Poisson equations. A proper design of GaN MOSFET n⁺nn⁺ channel with uncentered gate in n-region to reach the maximum detection sensitivity is proposed. It is shown that the main role in formation of longitudinal transport asymmetry and THz radiation detection is played by optical phonon emission process. It is found that the detection current at 300 K is maximal in frequency range from 0.5 to 7 THz. At higher frequenciea the detection current rapidly decreases due to the inertia of electron motion.

It has been theoretically predicted that light carrying orbital angular momentum, or twisted light, can be tuned to have a strong magnetic-field component at optical frequencies. We here consider the interaction of these peculiar fields with a semiconductor quantum dot and show that the magnetic interaction results in new types of optical transitions. In particular, a single pulse of such twisted light can drive light-hole-to-conduction band transitions that are cumbersome to produce using conventional Gaussian beams or even twisted light with dominant electric fields.

GaSb/InAs heterostructures were investigated for the enhancement of terahertz (THz) radiation from an InAs thin film excited by a femtosecond laser. Taking advantage of the large conduction band discontinuity between GaSb and InAs, electrons excited in the GaSb layer gain a large excess energy when injected into the InAs radiation layer. Enhancement of the THz radiation by a factor of approximately two was observed when the surface pinning position was controlled to reduce the surface electric field by the introduction of a thin InAs cap layer.

We present THz frequency range characterization of highly resistive (Cd,Mg)Te and (Cd,Mn)Te single crystals, using an "experiment-on-chip" configuration. We have demonstrated that both of these single crystals exhibit simultaneously strong photoconductive (PC) and electro-optic (EO) effects by performing measurements on a given single platelet with a deposited Au coplanar transmission line. We optically generated a subpicosecond electrical transient by focusing an ultraviolet 100-fs-wide pump pulse between the electrodes of a dc-biased coplanar line (PC effect) and, subsequently, time resolved it with a subpicosecond resolution along the transmission line using an internal EO effect by passing infrared, 100-fs-wide probe pulses through the crystal between the coplanar strips. Transients sampled at different distances from the generation site allowed us to calculate the complex propagation factor γ(f) of our transmission lines and the corresponding THz bandwidth attenuation and phase velocity. The latter parameters enabled us to reconstruct the original ∼600-fs-in-duration, PC-generated transient by "back-propagating" a signal to the excitation point. Furthermore, we have also determined the THz-bandwidth EO coefficients of our (Cd,Mn)Te and (Cd,Mg)Te crystals to be 6 pm/V and 1.2 pm/V, respectively.

We address the dynamics of two indistinguishable interacting particles moving on a dynamical percolation graph, i.e., a graph where the edges are independent random telegraph processes whose values jump between 0 and 1, thus mimicking percolation. The interplay between the particle interaction strength, initial state and the percolation rate determine different dynamical regimes for the walkers. We show that, whenever the walkers are initially localised within the interaction range, fast noise enhances the particle spread compared to the noiseless case.

The paper is focused on the investigation of magneto-transport phenomena in the compensated bulk-like GaN sample. Particularly, we studied the diffusion coefficient of the electrons in parallel and crossed configurations of moderate electric (E=1...10 kV/cm) and magnetic (H=1...4 T) fields. We found that E-field dependencies of the transverse-to-current diffusion coefficient are non-monotonic for both configurations with magnitude of the diffusion coefficient greatly controlled by the H-field. We showed that different behavior of the diffusion processes corresponds to distinct kinetics of the hot electrons. We suggest that measurements of the diffusion coefficient under E- and H-fields will allow to identify important for applications regimes of the electron kinetics.

The issue of quantum mechanical coupling between a semiconductor quantum dot and a quantum well is studied in two families of GaAs- and InP- based structures at cryogenic temperatures. It is shown that by tuning the quantum well parameters one can strongly disturb the 0D-character of the coupled system ground state, initially located in a dot. The out-coupling of either an electron or a hole state from the quantum dot confining potential is viewed by a significant elongation of the photoluminescence decay time constant. Band structure calculations show that in the GaAs-based coupled system at its ground state a hole remains isolated in the dot, whereas an electron gets delocalized towards the quantum well. The opposite picture is built for the ground state of a coupled system based on InP.

We investigated terahertz radiation from coherent GaAs-like longitudinal optical (LO) phonons in (11n)-oriented GaAs/In_0.1Al_0.9As strained multiple quantum wells for clarifying the screening effects of photogenerated carriers. We observed the intense quasi-monochromatic terahertz wave from the coherent GaAs-like LO phonon, which originates from the initial polarization enhanced by the strong piezoelectric field. The intensity of the coherent GaAs-like LO-phonon band exhibited a saturation behavior as the pump power was increased. We evaluated the saturation behavior in terms of excitation efficiency of the terahertz wave from the coherent GaAs-like LO phonon using the parameter of unit-power intensity. From the pump-power dependence of the unit-power intensity, we conclude that the screening effect of high density photogenerated carriers on the piezoelectric field causes saturation of the terahertz-wave intensity from the coherent GaAs-like LO phonon.

In the presence of a transverse magnetic field, the charge current in nanowires can flow from the hot to the cold reservoir, but also backwards. The sign change can be obtained by increasing the temperature bias or the magnetic field. This behavior occurs when the magnetic field is sufficiently strong. Here, we will investigate how the size of the anomalous backward-flowing current is affected by an electric field perpendicular to the nanowire. The interplay of the electric and magnetic field modifies the dispersion curves, which will show up in the transport properties. We will also investigate how the presence of impurities affects the anomalous current. The electric field affects backscattering due to impurities, and thus the thermoelectric current reversal. Preliminary results show that the current reversal can survive in the presence of impurities.

An azo dye was prepared through an environmentally benign and economically feasible synthesis route with cardanol as a starting material. Cardanol is a cost-effective and renewable natural source obtained from Cashew Nut Shell Liquid, a by-product of the cashew industry. The dye was spectrally characterized by IR, UV-Vis, NMR and fluorescence studies. UV-Vis absorption showed a bathochromic shift between solvents of lower and higher polarities. Nonlinear optical and photoacoustic properties were studied using a frequency doubled Nd:YAG laser producing 532 nm laser pulses of 3 ns pulse width. Results show that the nonlinear absorption coefficient decreases with the increase of on-axis intensity, suggesting excited state absorption as the principal mechanism. The observed nonlinearity has applications in optoelectronics.

We report on the numerical modelling of rectification in a gated two-dimensional electron gas. We demonstrate that drift-diffusion-based and energy-relaxation-based models predict different features of rectified terahertz radiation as a function of gate bias. Whereas the widely accepted mechanism for rectification is considered to be plasmonic-based, there are conditions when diffusion currents originating by non-local carrier heating can dominate the response. Moreover, diffusive contributions can substantially enhance the response becoming an important phenomenon, which has to be considered in future designs of efficient transistor-based terahertz rectifiers.

In this paper a new waveguide design is proposed to be implemented as part of Ballistic Deflection Transistor (BDT) Traveling Wave Amplifier Design. The BDT is designed to be operated in the Terahertz regime. Due to its relatively low transconductance (g_m=200µA/V), the entire structure will consist of ten stages, with 15 BDTs/stage, to reach a total gain of 30mA/V. In this case, the total length of the transmission line will be more than 400µm. We did the investigation for different structures and materials of the transmission line. For our Parallel Plate Dielectric Waveguide with Signal Line inserted (PPDWS) design, we are able to get an average loss of 0.46dB/mm at 0.8-1.4THz from ANSYS HFSS simulation. The return loss for input and output are better than -20dB at 0.8-1.7THz. Although it is designed for our future travelling wave amplifier, it can also be used for various other THz frequency applications.

Travelling coherent phonons can be actively used to manipulate the optical properties of semiconductor nanostructures on the picosecond time scale. Phonon wave packets that interact with a quantum dot (QD) ensemble can significantly vary the output intensity of a laser, which uses the QDs as active medium. Based on a recently developed theoretical model to describe this coupled phonon-QD-photon system, we here study how the laser response on phonon wave packets depends on several parameters, for example phonon pulse properties and laser pump rate.

Advanced selective doping provides effective tool for nanoscale engineering of potential barriers and photoelectron processes in quantum well (QW) and quantum dot (QD) optoelectronic nanomaterials for IR sensing and wide band photovoltaic conversion. Photoelectron kinetics and device characteristics are investigated theoretically and experimentally. Asymmetrical doping of QWs is employed in a double QW structure for tuning electron transitions in QWs by voltage bias. These QW devices demonstrate bias-tunable multicolor detection and capability of remote temperature sensing. The QD structures with bipolar doping are proposed to independently control photocarrier lifetime (photocurrent) and dark current. The bipolar doping allows us to increase the height of nanoscale potential barriers around QDs without changing the electron population in QDs, which determines dark current. The QD devices with bipolar doping demonstrate significant enhancement of photocurrent, while dark current is close to that in corresponding reference devices with unipolar doping.

We study numerically a multichannel electronic Mach-Zender interferometer, where an orthogonal magnetic field produces edge states. Our time-dependent model is based on the split-step Fourier method and describes the charge carrier as a Gaussian wavepacket of edge states, whose path is defined by split-gate induced potential profiles on the 2DEG at filling factor ν = 2. We analyse a beam splitter with ∼ 50% inter-channel mixing and obtain Aharonov-Bohm oscillations in the transmission probability of the second channel.