arXiv subjects

Werner Dietsche

Publications and source records attributed to Werner Dietsche.

13 recordsLinked to original sources

arXiv2025

Charge Transfer Dynamics in an Electron-Hole Bilayer Device: Capacitance Oscillations and Hysteretic Behavior

The capacitance and differential conductance of MBE-grown AlGaAs/GaAs p-i-n diodes are investigated. In these diodes, the p-doped layer, an adjacent intrinsic spacer, and a central barrier are made of AlGaAs. Capacitance oscillations and hysteretic behavior are observed and understood to be consequences of the AlGaAs spacer properties. These findings have significant implications for the design of heterostructures aimed at achieving electrically contacted, closely spaced electron and hole layers.

cond-mat.mes-hall↗

arXiv2024

Memory resistor based in GaAs 2D-bilayers: In and out of equilibrium

Resonant tunneling between closely spaced two dimensional electron gases is a single particle phenomenon that has sparked interest for decades. High tunneling conductances at equal electron densities are observed whenever the Fermi levels of the two quantum wells align. Detuning the Fermi levels out of the resonant 2D-2D tunneling regime causes a negative differential resistance. The negative differential resistance leads to a hysteresis when operating the device in a current driven mode, allowing a bilayer system to function as a volatile memory resistor.

cond-mat.mes-hall↗

arXiv2023

Controlled generation and detection of a thermal bias in Corbino devices under the quantum Hall regime

We present an experimental technique to generate and measure a temperature bias in the quantum Hall effect of GaAs/AlGaAs Corbino samples. The bias is generated by injecting an electrical current at a central resistive heater and the resulting radial temperature drop is determined by conductance measurements at internal and external concentric rings. The experimental results agree with the predictions of numerical simulations of the heat flow through the substrate. We also compare these results with previous predictions based on the thermoelectric response of these devices

cond-mat.mes-hall↗

arXiv2021

The improved inverted AlGaAs/GaAs interface: its relevance for high-mobility quantum wells and hybrid systems

Two dimensional electron gases (2DEGs) realized at GaAs/AlGaAs single interfaces by molecular-beam epitaxy (MBE) reach mobilities of about 15 million cm^2/Vs if the AlGaAs alloy is grown after the GaAs. Surprisingly, the mobilities may drop to a few millions for the identical but inverted AlGaAs/GaAs interface, i.e. reversed layering. Here we report on a series of inverted heterostructures with varying growth parameters including temperature, doping, and composition. Minimizing the segregation of both dopants and background impurities leads to mobilities of 13 million cm^2/Vs for inverted structures. The dependence of the mobility on electron density tunes by a gate or by illumination is found to be the identical if no doping layers exist between the 2DEG and the respective gate. Otherwise, it differs significantly compared to normal interface structures. Reducing the distance of the 2DEG to the surface down to 50nm requires an additional doping layer between 2DEG and surface in order to compensate for the surface-Schottky barrier. The suitability of such shallow inverted structures for future semiconductor-superconductor hybrid systems is discussed. Lastly, our understanding of the improved inverted interface enables us to produce optimized double-sided doped quantum wells exhibiting an electron mobility of 40 million cm^2/Vs at 1K.

physics.app-ph↗

arXiv2021

Donor implanted Back-gates in GaAs for MBE-grown highest mobility two-dimensional electron systems

Three different elements, Silicon, Selenium, and Tellurium, are ion-implanted in Gallium arsenide to form a conducting layer that serves as a back-gate to a molecular beam epitaxy (MBE) overgrown two-dimensional electron gas (2DEG). While the heavy ion Tellurium creates too many damages in the gallium arsenide to form a conducting layer, both Silicon and Selenium show promising results combined with MBE-grown high-quality 2DEGs. Similar 2DEG mobility compared to non-implanted reference samples is achieved for both Silicon and Selenium implanted structures. Individual contacts to the back-gate are challenging. However, Silicon implanted structures, annealed before the MBE growth, result in a function back-gate, and the electron density of the 2DEG is tuned via the back-gate.

physics.app-ph↗

arXiv2021

Thermoelectric cooling properties of a quantum Hall Corbino device

We analyze the thermoelectric cooling properties of a Corbino device in the quantum Hall regime on the basis of experimental data of electrical conductance. We focus on the cooling power and the coefficient of performance within and beyond linear response. Thermovoltage measurements in this device reported in {\em Phys. Rev. Applied, {\bf 14} 034019 (2020)} indicated that the transport takes place in the diffusive regime, without signatures of effects due to the electron-phonon interaction in a wide range of temperatures and filling factors. In this regime, the heat and charge currents by electrons can be described by a single transmission function. We infer this function from experimental data of conductance measurements and we calculate the cooling power and the coefficient of performance for a wide range of filling factors and temperatures, as functions of the thermal and electrical biases. We predict an interesting cooling performance in several parameter regimes.

cond-mat.mes-hall↗

arXiv2020

Thermoelectricity in Quantum-Hall Corbino Structures

We measure the thermoelectric response of Corbino structures in the quantum Hall effect regime and compare it with a theoretical analysis. The measured thermoelectric voltages are qualitatively and quantitatively simulated based upon the independent measurement of the conductivity indicating that they originate predominantly from the electron diffusion. Electron-phonon interaction does not lead to a phonon-drag contribution in contrast to earlier Hall-bar experiments. This implies a description of the Onsager coefficients on the basis of a single transmission function, from which both thermovoltage and conductivity can be predicted with a single fitting parameter. It furthermore let us predict a figure of merit for the efficiency of thermoelectric cooling which becomes very large for partially filled Landau levels (LL) and high magnetic fieldse of merit can be estimated which becomes very large for partially filled Landau levels and high magnetic fields.

cond-mat.mes-hall↗

arXiv2018

Scanning Gate Microscopy in a Viscous Electron Fluid

We measure transport through a Ga[Al]As heterostructure at temperatures between 0.1 K and 30 K. Increasing the temperature enhances the electron-electron scattering rate and viscous effects in the two-dimensional electron gas arise. To probe this regime we measure so-called vicinity voltages and use a voltage-biased scanning tip to induce a movable local perturbation. We find that the scanning gate images differentiate reliably between the different regimes of electron transport. Our data are in good agreement with recent theories for interacting electron liquids in the ballistic and viscous regimes stimulated by measurements in graphene. However, the range of temperatures and densities where viscous effects are observable in Ga[Al]As are very distinct from the graphene material system.

cond-mat.mes-hall↗

arXiv2016

Improvement of the transport properties of a high-mobility electron system by intentional parallel conductance

We present a gating scheme to separate even strong parallel conductance from the magneto-transport signatures and properties of a two-dimensional electron system. By varying the electron density in the parallel conducting layer, we can study the impact of mobile charge carriers in the vicinity of the dopant layer on the properties of the two-dimensional electron system. It is found that the parallel conducting layer is indeed capable to screen the remote ionized impurity potential fluctuations responsible for the fragility of fractional quantum Hall states.

cond-mat.mes-hall↗

arXiv2016

Structured Back Gates for High-Mobility Two-Dimensional Electron Systems Using Oxygen Ion Implantation

We present a new approach of back gate patterning that is compatible with the requirements of highest mobility molecular beam epitaxy. Contrary to common back gating techniques, our method is simple, reliable and can be scaled up for entire wafers. The back gate structures are defined by local oxygen implantation into a silicon doped GaAs epilayer, which suppresses the conductance without affecting the surface quality.

cond-mat.mes-hall↗

arXiv2015

Mapping an electron wave function by a local electron scattering probe

A technique is developed which allows for the detailed mapping of the electronic wave function in two-dimensional electron gases with low-temperature mobilities up to 15E6 cm^2/Vs. Thin ("delta") layers of aluminium are placed into the regions where the electrons reside. This causes electron scattering which depends very locally on the amplitude of the electron wave function at the position of the Al "delta"-layer. By changing the distance of this layer from the interface we map the shape of the wave function perpendicular to the interface. Despite having a profound effect on the electron mobiliy, the "delta"-layers do not cause a widening of the quantum Hall plateaus.

cond-mat.mes-hall↗

arXiv2014

Interplay between the coherent and incoherent transport in quantum Hall bilayers

We systematically study the coherent transport (Josephson tunneling and counterflow current) and its breakdown which leads to incoherent charge flow in in the excitonic BCS condensate formed in GaAs bilayers at $ν_{tot}=1/2+1/2$. The Josephson currents in samples with three different interlayer distances vary by four orders of magnitude. In contrast, the breakdown thresholds for the $ν_{tot}=1$ quantum Hall state are comparable. Furthermore, Coulomb drag in a Corbino ring reveals that the coherent counterflow current coexists with the dissipative charge transport.

cond-mat.mes-hall↗

arXiv2014

Increasing the ν = 5 / 2 gap energy: an analysis of MBE growth parameters

The fractional quantized Hall state (FQHS) at the filling factor ν = 5/2 is of special interest due to its possible application for quantum computing. Here we report on the optimization of growth parameters that allowed us to produce two-dimensional electron gases (2DEGs) with a 5/2 gap energy up to 135 mK. We concentrated on optimizing the MBE growth to provide high 5/2 gap energies in "as-grown" samples, without the need to enhance the 2DEGs properties by illumination or gating techniques. Our findings allow us to analyse the impact of doping in narrow quantum wells with respect to conventional DX-doping in AlxGa1-xAs. The impact of the setback distance between doping layer and 2DEG was investigated as well. Additionally, we found a considerable increase in gap energy by reducing the amount of background impurities. To this end growth techniques like temperature reductions for substrate and effusion cells and the reduction of the Al mole fraction in the 2DEG region were applied.

cond-mat.mes-hall↗