황의헌 교수

Carrier transport in gated 2D graphene monolayers is considered in the presence of scattering by random charged impurity centers with density n(i). Excellent quantitative agreement is obtained (for carrier density n>10(12) cm(-2)) with existing experimental data. The conductivity scales linearly with n/n(i) in the theory. We explain the experimentally observed asymmetry between electron and hole conductivities, and the high-density saturation of conductivity for the highest mobility samples. We

We theoretically calculate the phonon scattering limited electron mobility in extrinsic (i.e., gated or doped with a tunable and finite carrier density) two-dimensional graphene layers as a function of temperature $(T)$ and carrier density $(n)$. We find a temperature-dependent phonon-limited resistivity ${\ensuremath{\rho}}_{\mathit{ph}}(T)$ to be linear in temperature for $T\ensuremath{\gtrsim}50\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ with the room-temperature intrinsic mobility reaching the va

Correction for 'Surface group modification and carrier transport properties of layered transition metal carbides (Ti2CTx, T: -OH, -F and -O)' by Shen Lai, et al., Nanoscale, 2015, DOI: 10.1039/c5nr06513e.

We calculate the temperature-dependent conductivity of graphene in the presence of randomly distributed Coulomb impurity charges arising from the temperature-dependent screening of the Coulomb disorder without any phonons. The purely electronic temperature dependence of our theory arises from two independent mechanisms: the explicit temperature dependence of the finite-temperature dielectric function $\ensuremath{\epsilon}(q,T)$ and the finite-temperature energy averaging of the transport scatte

We derive the plasmon dispersion in doped double-layer graphene (DLG), made of two parallel graphene monolayers with carrier densities ${n}_{1}$ and ${n}_{2}$, respectively, and an interlayer separation of $d$. The linear chiral gapless single-particle energy dispersion of graphene leads to DLG plasmon properties with several unexpected experimentally observable characteristic features such as a nontrivial influence of an undoped $({n}_{2}=0)$ layer on the DLG plasmon dispersion and a strange in

We theoretically calculate and compare the single particle relaxation time $({\ensuremath{\tau}}_{s})$ defining the quantum level broadening and the transport scattering time $({\ensuremath{\tau}}_{t})$ defining the Drude conductivity in two-dimensional (2D) graphene layers in the presence of screened charged impurity scattering and short-range defect scattering. We find that the ratio ${\ensuremath{\tau}}_{t}∕{\ensuremath{\tau}}_{s}$ strongly increases with increasing ${k}_{F}{z}_{i}$ and $\ens

Motivated by recent experiments by Yuri M. Zuev et al. [Phys. Rev. Lett. 102, 096807 (2009)], Peng Wei et al. [Phys. Rev. Lett. 102, 166808 (2009)], and Joseph G. Checkelsky et al. [Phys. Rev. B 80, 081413(R) (2009)], we calculate the thermopower of graphene incorporating the energy dependence of various transport scattering times. We find that scattering by screened charged impurities gives a reasonable explanation for the measured thermopower. The calculated thermopower behaves as $1/\sqrt{n}$

Motivated by a recent experiment reporting on the possible application of graphene as sensors, we calculate transport properties of two-dimensional graphene monolayers in the presence of adsorbed molecules. We find that the adsorbed molecules, acting as compensators that partially neutralize the random charged impurity centers in the substrate, enhance the graphene mobility without much change in the carrier density. We predict that subsequent field-effect measurements should preserve this highe

We calculate the screening function in bilayer graphene (BLG) in both the intrinsic (undoped) and the extrinsic (doped) regimes within the random phase approximation, comparing our results with the corresponding single layer graphene and the regular two-dimensional electron gas. We find that the Kohn anomaly is strongly enhanced in BLG. We also discuss the Friedel oscillation and the RKKY interaction, which are associated with the nonanalytic behavior of the screening function at q=2k(F). We fin

Collective excitations of coupled electron-phonon systems are calculated for both monolayer and bilayer graphenes, taking into account the nonperturbative Coulomb coupling between electronic excitations in graphene and the substrate longitudinal-optical phonon modes. We find that the plasmon-phonon coupling in monolayer graphene is strong at all densities but in bilayer graphene the coupling is significant only at high densities satisfying the resonant condition ${\ensuremath{\omega}}_{pl}\ensur

Sensory adaptation is an essential part of biological neural systems for sustaining human life. Using the light-induced halide phase segregation of CsPb(Br_1-<i>x</i>I_<i>x</i>)₃ perovskite, we introduce neuromorphic phototransistors that emulate human sensory adaptation. The phototransistor based on a hybrid structure of perovskite and transition-metal dichalcogenide (TMD) emulates the sensory adaptation in response to a continuous light stimulus, similar to the n

We consider hot-carrier inelastic scattering due to electron-electron interactions in graphene as functions of carrier energy and density. We calculate the imaginary part of the zero-temperature quasiparticle self-energy for doped graphene utilizing the ${G}_{0}W$ and random phases approximations. Using the full dynamically screened Coulomb interaction, we obtain the inelastic quasiparticle lifetimes and associated mean free paths. The linear dispersion of graphene gives lifetime energy dependen

We calculate the electron self-energy as well as the quasiparticle spectral function in doped graphene, taking into account electron-electron interaction in the leading order dynamically screened Coulomb coupling and electron-impurity interaction associated with quenched disorder. Our theory provides the basis for calculating all one-electron properties of extrinsic graphene. Comparison with existing angle-resolved photoemission spectroscopy measurements shows broad qualitative and semiquantitat

Considering scattering by unintentional background charged impurities and by charged dopants in the modulation doping layer as well as by GaAs acoustic phonons, we theoretically consider the practical intrinsic (phonons) and extrinsic (background and dopants) limits to carrier mobility in modulation-doped AlGaAs-GaAs two-dimensional (2D) semiconductor structures. We find that reducing background impurity density to ${10}^{12}\text{ }{\text{cm}}^{\ensuremath{-}3}$ along with a modulation doping s

We demonstrate the application of MXenes, metallic 2D materials of transition-metal carbides, as excellent electrode materials for photonic devices. In this study, we have fabricated an InSe-based photodetector with a Ti₂CT_<i>x</i> electrode. The photodetector with few-layer, atomically thin, Ti₂CT_<i>x</i> (MXene) electrodes shows the avalanche carrier multiplication effect, which leads to high device performance. To improve the performance of the InSe