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  • Küçük Resim
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    A comparative study of transport properties of monolayer graphene and AlGaN-GaN heterostructure
    (American Institute Physics, 2015) Özdemir, Mustafa; Atasever, Ö.; Özdemir, Berrin; Yarar, Zeki; Özdemir, Meryem
    The electronic transport properties of monolayer graphene are presented with an Ensemble Monte Carlo method where a rejection technique is used to account for the occupancy of the final states after scattering. Acoustic and optic phonon scatterings are considered for intrinsic graphene and in addition, ionized impurity and surface roughness scatterings are considered for the case of dirty graphene. The effect of screening is considered in the ionized impurity scattering of electrons. The time dependence of drift velocity of carriers is obtained where overshoot and undershoot effects are observed for certain values of applied field and material parameters for intrinsic graphene. The field dependence of drift velocity of carriers showed negative differential resistance and disappeared as acoustic scattering becomes dominant for intrinsic graphene. The variation of electron mobility with temperature is calculated for intrinsic (suspended) and dirty monolayer graphene sheets separately and they are compared. These are also compared with the mobility of two dimensional electrons at an AlGaN/GaN heterostructure. It is observed that interface roughness may become very effective in limiting the mobility of electrons in graphene.
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    Öğe
    Calculation of electronic properties of multilayer graphene with Monte Carlo method
    (American Institute Physics, 2016) Atasever, O.; Özdemir, Mustafa D.; Özdemir, Berrin; Yarar, Zeki; Özdemir, Metin; Akkus, B; Oktem, Y; Yalcin, LS; Mutlu, RBC; Dogan, GS
    In this study, the electronic transport properties of bilayer graphene is investigated by an ensemble Monte Carlo method. The bilayer graphene has a quadratic energy dependence on wave vector near the points known as Dirac points in the reciprocal lattice. For bilayer graphene the scatterings due to acoustic and optic phonons and ionized impurities are taken into account. Velocity-time and steady state velocity-applied field curves are obtained and from the slope of velocity-field curves at low fields, the low field mobility of bilayer graphene is obtained. The dependence of mobility of bilayer graphene on temperature, electron concentration, impurity concentration, acoustic and optic deformation constants is investigated and it is observed that the most important mechanism limiting the mobility is the phonon scattering.
  • Küçük Resim
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    Electron transport properties of silicene: Intrinsic and dirty cases with screening effects
    (Elsevier, 2020) Özdemir, Mustafa D.; Çekil, H. C.; Atasever, Ö. S.; Özdemir, Berrin; Yarar, Zeki; Özdemir, Metin
    The electronic transport characteristics of silicene sheets are studied by an Ensemble Monte Carlo (EMC) technique in the presence of phonon (acoustic, non-polar optic, surface polar optic), surface roughness and ionized impurity scattering mechanisms. Both intrinsic and silicene on an Al2O3 substrate are considered. Screening is also considered for both ionized impurity and surface polar optic phonon scattering of electrons. The velocity-applied field characteristics are obtained for both cases. A negative differential resistance (NDR) behaviour is observed for intrinsic case only. The mobility of carriers are calculated as a function of temperature for both cases and the results are compatible with existing experimental results and theoretical predictions. The effects of screening and flexural phonons on mobility are also studied.
  • Küçük Resim
    Öğe
    Transport properties of graphene and suspended graphene with EMC: The role of various scattering mechanisms
    (SPRINGER, 2016) Özdemir, Mustafa.; Atasever, Ö. S.; Özdemir, Berrin; Yarar, Zeki; Özdemir, Metin
    The electronic transport properties of graphene and suspended (intrinsic) graphene sheets are studied using an ensemble Monte Carlo (EMC) technique. The combined scattering mechanisms that are taken into account for both cases are nonpolar optic and acoustic phonons, ionized impurity, interface roughness, and surface polar phonon scatterings. The effect of screening is also considered in the ionized impurity and surface polar phonon scatterings of electrons. A rejection technique is used in EMC simulations to account for the occupancy of the final states. Velocity-field characteristics of graphene and suspended graphene sheets are obtained using various values of acoustic deformation potential constants. The variation of electron mobility of graphene is studied as a function of electron concentration and its variation as a function of temperature are investigated for the case of suspended graphene. For the former case, the mobility increases with electron concentration first and after a certain value of electron concentration it begins to decrease, while for the latter case the mobility decreases almost linearly with temperature. The mobility results from EMC simulations are compatible with the existing experimental studies for the unsuspended graphene case.