Graphene-based devices show $1/f$ low-frequency noise in several electronic transport properties, such as mobility and charge carrier concentration. The recent outburst of experimental studies on graphene-based devices integrated into circuit quantum electrodynamics systems has rekindled the interest in low-frequency charge noise. We investigate charge carrier density noise in graphene within the McWorther model where noise is induced by electron traps in the substrate. We focus on the large doping regime and introduce a simple modelization of the effect of localized/delocalized traps in terms of single/double spin occupancy of trap states. We find that in both cases the charge carrier spectrum of graphene obeys the $1/f^α$ power-law behavior where $α$ is very close to the unity, and for each case we evaluate the deviation $β=1-α$. The amplitude of the noise is found to depend on the trap energy distribution and on temperature. Single/double spin occupancy of trap states influences the temperature dependence of noise amplitude only to second order.
In this paper, the recent advances of our studies on hot carrier degradation (HCD) are presented from trap-based approach. The microscopic speculation of interface trap generation is carried out by time-dependent DFT (TDDFT) simulation in "real-time". Two types of oxide traps contributing to HCD are identified from experiments. Combining the contributions of interface and oxide traps, a unified compact model has been proposed which can accurately predict hot carrier degradation and variation in full Vgs/Vds bias. The trap locations, degradation contributions and temperature dependence are stud…
Nanocrystals of AgInS$_2$ demonstrate giant Stokes shifts ~ 1 eV, the nature of which is still not clearly understood. We propose a theoretical model of this phenomenon bringing together several different mechanisms previously considered only separately. We take into account the contribution of electron-electron interaction with the hybrid density functional theory, as well as the renormalization of energy spectrum due to the electron-phonon coupling. Furthermore, we consider the presence of at least one point defect responsible for hole trapping and the formation of a localized polaron state.…
We consider the problem of confining the famously elusive Dirac-like quasiparticles, as found in some recently discovered low-dimensional systems. After briefly surveying the existing theoretical proposals for creating bound states in Dirac materials, we study relativistic excitations with a position-dependent mass term. With the aid of an exactly-solvable model, we show how bound states begin to emerge after a critical condition on the size of the mass term is met. We also reveal some exotic properties of the unusual confinement discovered, including an elegant chevron structure of the bound …
Metal halide perovskites quantum dots (MHPQDs) have aroused enormous interesting in the photovoltaic and photoelectric because of their marvelous properties and size characteristics. However, one of key problems that how to systematically analyze charge carriers trapping by different defects is still a challenge task. Here, we study nonradiation multiphonon processes of the charge carrier trapping by various defects in MHPQDs based on the well-known Huang-Rhys model, in which a method of fullconfiguration defect, including different defect species with variable depth and lattice relaxation str…
We have investigated the temperature dependence of the photoluminescence spectra and average photoluminescence decay rate of CdTe quantum dot monolayers of different sizes as a function of concentration in the range 77 K to 296 K. It is shown that a simple three level analytic model involving bright and dark exciton states can only describe the lower temperature data but is unable to satisfactorily fit the data over the full temperature range. An extended model which includes external trap states is necessary to fit the data above approximately 150 K. Parameters for the model are obtained usin…
Molecular materials have emerged as highly tunable materials for photovoltaic and light-harvesting applications. The most severe challenge of this class of materials is the trapping of charge carriers in bound electron-hole pairs, which severely limits the free charge carrier generation. Here, we demonstrate a significant modification of the exciton dynamics of thin films of endohedral metallofullerene complexes upon alkali metal intercalation. For the exemplary case of Sc$_3$N@C$_{80}$ thin films, we show that potassium intercalation results in an additional relaxation channel for the optical…
Fluorescence Intermittency of A Single Quantum System and Anderson Localization
提出了半导体量子点和单分子荧光猝灭的本质是安德森局域化的表现。\emph{on}时间的幂律分布被解释为由于QD/SM与随机环境之间的相互作用。特别是，我们发现\emph{on}时间概率分布在局域化和非局域化状态下表现不同。当适当缩放时，它们是用于不同QD/SM系统的\emph{universal}。在非定域QD/SM区域中的\emph{on} -时间概率分布函数可以近似为指数覆盖$-2\le m <0$的幂律。当QD/SM的电荷跳跃到陷阱态时，QD/SM切换到暗（\emph{off}）态，其在被周围基质稳定后变得局部化。
Transient reflectivity (TR) measured at laser photon energy 1.51 eV from the indirectly intersurface coupled topological insulator Bi2-xMnxSe3 films (12 nm thick) revealed a strong dependence of the rise-time and initial decay-time constants on photoexcited carrier density and Mn content. In undoped samples (x = 0), these time constants are exclusively governed by electron-electron and electron-phonon scattering, respectively, whereas in films with x = 0.013 - 0.27 ultrafast carrier dynamics are completely controlled by photoexcited electron trapping by ionized Mn2+ acceptors and their dimers.…
Moiré superlattice-induced sub-bands in twisted van der Waals homo- and hetero-structures govern their optical and electrical properties, rendering additional degrees of freedom such as twist angle. Here, we demonstrate the moiré superlattice effects on the intralayer excitons and trions in a twisted bilayer of MoS$_2$ of H-type stacking at marginal twist angles. We identify the emission from localized and multiple delocalized sub-bands of intralayer moiré excitons and show their electrical modulation by the corresponding trion formation. The electrical control of the oscillator strength of th…
This work presents theoretical demonstration of a carrier trap unit formed by dual topological insulator constrictions (TIC) on the HgTe/CdTe quantum well (QW) with inverted band structures. The sample of HgTe/CdTe QW is patterned into a Hall bar device and a topological quantum dot is created by adding split gate electrodes closely on the QW. In sharp contrast to conventional semiconductor quantum dots, the presence or absence of topological edge states in the proposed quantum hall bar system leads to distinct propagating/insulating state of the TICs with large on/off ratio. This topological …
Strong Coulomb interactions in two-dimensional systems, together with quantum confinement, make many-body processes particularly effective for carrier dynamics, which plays a crucial role in determining carrier lifetime, photoconductivity, and emission yield of the materials. Hereby, by using optical pump and terahertz probe spectroscopy, we have investigated the photocarrier dynamics in the PdSe2 films with different thickness. The experimental results reveal that the photocarrier relaxation consists of two components: a fast component of 2.5 ps that shows the layer-thickness independence, an…
We study laterally trapped dipolar exciton ensembles in coupled GaAs quantum wells at high magnetic fields in the Faraday configuration. In photoluminescence experiments, we identify three magnetic field regimes. At low fields, the exciton density is increased by a reduced charge carrier escape from the trap, and additionally, the excitons' emission energy is corrected by a positive diamagnetic shift. At intermediate fields, magnetic field dependent correction terms apply which follow the characteristics of a neutral magnetoexciton. Due to a combined effect of an increasing binding energy and …
