We report on time-resolved Kerr rotation measurements of spin coherence of electrons in the first excited subband of a high-mobility low-density two-dimensional electron system in a GaAs/Al0.35Ga0.65As heterostructure. While the transverse spin lifetime (T2*) of electrons decreases monotonically with increasing magnetic field, it has a non-monotonic dependence on the temperature, with a peak value of 596 ps at 36 K, indicating the effect of inter-subband electron-electron scattering on the electron spin relaxation. The spin lifetime may be long enough for potential device application with electrons in excited subbands.
The low-temperature resistance of a conducting LaAlO3/SrTiO3 interface with a 10 nm thick LaAlO3 film decreases by more than 50% after illumination with light of energy higher than the SrTiO3 band-gap. We explain our observations by optical excitation of an additional high mobility electron channel, which is spatially separated from the photo-excited holes. After illumination, we measure a strongly non-linear Hall resistance which is governed by the concentration and mobility of the photo-excited carriers. This can be explained within a two-carrier model where illumination creates a high-mobil…
We present new data and a compact mobility model for single-wall carbon nanotubes, with only two adjustable parameters, the elastic and inelastic collision mean free paths at 300 K. The mobility increases with diameter, decreases with temperature, and has a more complex dependence on charge density. The model and data suggest the room temperature mobility does not exceed 10,000 cm2/V.s at high carrier density (n > 0.5 nm-1) for typical single-wall nanotube diameters, due to the strong scattering effect of the second subband.
Effective electron mobilities are obtained by transport measurements on InAs nanowire field-effect transistors at temperatures ranging from 10-200 K. The mobility increases with temperature below ~ 30 - 50 K, and then decreases with temperature above 50 K, consistent with other reports. The magnitude and temperature dependence of the observed mobility can be explained by Coulomb scattering from ionized surface states at typical densities. The behaviour above 50 K is ascribed to the thermally activated increase in the number of scatterers, although nanoscale confinement also plays a role as hig…
A simulation framework that couples atomistic electronic structures to Boltzmann transport formalism is developed and applied to calculate the transport characteristics of thin silicon nanowires (NWs) up to 12nm in diameter. The sp3d5s*-spin-orbit-coupled atomistic tight-binding (TB) model is used for the electronic structure calculation. Linearized Boltzmann transport theory is applied, including carrier scattering by phonons, surface roughness (SRS), and impurities. We present a comprehensive investigation of the low-field mobility in silicon NWs considering: i) n- and p-type NWs, ii) [100],…
For applications to sensor design, the product nxmu of the electron density n and the mobility mu is a key parameter to be optimized for enhanced device sensitivity. We model the carrier mobility in a two dimensional electron gas (2DEG) layer developed in a delta-doped heterostructure. The subband energy levels, electron wave functions, and the band-edge profile are obtained by numerically solving the Schrodinger and Poisson equations self-consistently. The electron mobility is calculated by including contributions of scattering from ionized impurities, the background neutral impurities, the d…
A novel 2-dimensional electron gas (2DEG) system with high-mobility was discovered at the interface of two perovskite oxides, a polar orthorhombic perovskite LaScO3 (LSO) and a nonpolar cubic perovskite BaSnO3 (BSO). Upon depositing the LSO film on the BSO film, the conductance enhancement and the resulting 2DEG density (n2D) was measured. Comparing the results with the previously reported LaInO3/BaSnO3 (LIO/BSO) polar interface, we applied the interface polarization model to the LSO/BSO system, in which the polarization exists only over 4 pseudocubic unit cells in LSO from the interface and v…
We investigate the effects of electron and acoustic-phonon confinement on the low-field electron mobility of thin square silicon nanowires (SiNWs) that are surrounded by SiO$_2$ and gated. We employ a self-consistent Poisson-Schrödinger-Monte Carlo solver that accounts for scattering due to acoustic phonons (confined and bulk), intervalley phonons, and the Si/SiO$_2$ surface roughness. The wires considered have cross sections between 3 $\times$ 3 nm$^2$ and 8 $\times$ 8 nm$^2$. For larger wires, as expected, the dependence of the mobility on the transverse field from the gate is pronounced. At…
Lead halide perovskite semiconductors are soft, polar, materials. The strong driving force for polaron formation (the dielectric electron-phonon coupling) is balanced by the light band effective-masses, leading to a strongly-interacting large-polaron. A first-principles prediction of mobility would help understand the fundamental mobility limits. Theories of mobility need to consider the polaron (rather than free-carrier) state due to the strong interactions. In this material we expect that at room temperature polar-optical phonon mode scattering will dominate, and so limit mobility. We calcul…
A decade of intense research on two-dimensional (2D) atomic crystals has revealed that their properties can differ greatly from those of the parent compound. These differences are governed by changes in the band structure due to quantum confinement and are most profound if the underlying lattice symmetry changes. Here we report a high-quality 2D electron gas in few-layer InSe encapsulated in hexagonal boron nitride under an inert atmosphere. Carrier mobilities are found to exceed 1,000 and 10,000 cm2/Vs at room and liquid-helium temperatures, respectively, allowing the observation of the fully…
In order to characterize magnetic-field (B) tunable THz plasmonic detectors, spectroscopy experiments were carried out at liquid helium temperatures and high magnetic fields on devices fabricated on a high electron mobility GaAs/AlGaAs heterostructure. The samples were either gated (the gate of a meander shape) or ungated. Spectra of a photovoltage generated by THz radiation were obtained as a function of B at a fixed THz excitation from a THz laser or as a function of THz photon frequency at a fixed B with a Fourier spectrometer. In the first type of measurements, the wave vector of magnetopl…
$\mathrmβ$-Gallium oxide ($\mathrm{β\mbox{-}Ga_{2}O_{3}}$) is an emerging widebandgap semiconductor for potential application in power and RF electronics applications. Initial theoretical calculation on a 2-dimensional electron gas (2DEG) in $\mathrm{β\mbox{-}(Al_{x}Ga_{1-x})_{2}O_{3}/Ga_{2}O_{3}}$ heterostructures show the promise for high speed transistors. However, the experimental results do not get close to the predicted mobility values. In this work, We perform more comprehensive calculations to study the low field 2DEG transport properties in the $\mathrm{β\mbox{-}(Al_{x}Ga_{1-x})_{2}O_…
We have studied the charge to spin conversion in Bi$_{1-x}$Sb$_x$/CoFeB heterostructures. The spin Hall conductivity (SHC) of the sputter deposited heterostructures exhibits a high plateau at Bi-rich compositions, corresponding to the topological insulator phase, followed by a decrease of SHC for Sb-richer alloys, in agreement with the calculated intrinsic spin Hall effect of Bi$_{1-x}$Sb$_x$ alloy. The SHC increases with increasing thickness of the Bi$_{1-x}$Sb$_x$ alloy before it saturates, indicating that it is the bulk of the alloy that predominantly contributes to the generation of spin c…
Recent demonstrations of inverted thermal activation of charge mobility in polymer field-effect transistors have excited the interest in transport regimes not limited by thermal barriers. However, rationalization of the limiting factors to access such regimes is still lacking. An improved understanding in this area is critical for development of new materials, establishing processing guidelines, and broadening of the range of applications. Here we show that precise processing of a diketopyrrolopyrrole-tetrafluorobenzene-based electron transporting copolymer results in single crystal-like and v…
The coupling of optical and electronic degrees of freedom together with quantum confinement in low-dimensional electron systems is particularly interesting for achieving exotic functionalities in strongly correlated oxide electronics. Recently, high room-temperature mobility has been achieved for a large bandgap transparent oxide - BaSnO$_3$ upon extrinsic La or Sb doping, which has excited significant research attention. In this work, we report the observation of room-temperature ferromagnetism in BaSnO$_3$ thin films and the realization of a two-dimensional electron gas (2DEG) on the surface…
High mobility two-dimensional electron gases (2DEGs) underpin today's silicon based devices and are of fundamental importance for the emerging field of oxide electronics. Such 2DEGs are usually created by engineering band offsets and charge transfer at heterointerfaces. However, in 2011 it was shown that highly itinerant 2DEGs can also be induced at bare surfaces of different transition metal oxides where they are far more accessible to high resolution angle resolved photoemission (ARPES) experiments. Here we review work from this nascent field which has led to a systematic understanding of th…
Recent ultrafast experiments have implicated intrachain base-stacking rather than base-pairing as the crucial factor in determining the fate and transport of photoexcited species in DNA chains. An important issue that has emerged concerns whether or not a Frenkel excitons is sufficient one needs charge-transfer states to fully account for the dynamics. In we present an $SU(2)\otimes SU(2)$ lattice model which incorporates both intrachain and interchain electronic interactions to study the quantum mechanical evolution of an initial excitonic state placed on either the adenosine or thymidine sid…
Two-dimensional vertically polarized Hg3AsSe4I monolayer for efficient photocatalytic water-splitting: promoting carrier separation by intrinsic electric field and Rashba effect
Frontier Institute of Science and Technology, State Key Laboratory of Electrical Insulation and Power Equipment, Xi’an Jiaotong University（西安交通大学前沿科学研究所、电气绝缘与电源设备国家重点实验室）；Key Lab of advanced optoelectronic quantum architecture and measurement (MOE), Beijing Key Laboratory of Quantum Matter State Control and Ultra-Precision Measurement Technology, and School of Physics, Beijing Institute of Technology（北京理工大学物理学院、光电量子架构与测量教育部重点实验室、北京市量子物质态控制与超精密测量技术重点实验室）
Electronic carriers in graphene show a high carrier mobility at room temperature. Thus, this system is widely viewed as a potential future charge-based high-speed electronic-material to complement- or replace- silicon. At the same time, the spin properties of graphene have suggested improved capability for spin-based electronics or spintronics, and spin-based quantum computing. As a result, the detection, characterization, and transport of spin have become topics of interest in graphene. Here we report a microwave photo-excited transport study of monolayer and trilayer graphene that reveals an…
