Somphonsane, Ratchanok

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Preferred name
Somphonsane, Ratchanok
Alternative Name
Somphonsane, R.
Main Affiliation
Email
ratchanok.so@kmitl.ac.th

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    Item type:Publication,
    Probing charge trapping and joule heating in graphene field-effect transistors by transient pulsing
    (2017-07-24)
    Ramamoorthy, H.
    ;
    Somphonsane, R.
    ;
    Radice, J.
    ;
    He, G.
    ;
    Nathawat, J.
    We use pulsed electrical studies to investigate the various processes that limit the current carrying capacity of graphene high frequency transistors. By investigating the transient response of these devices over a time scale that spans some twelve orders of magnitude, we identify the presence of four distinct processes that degrade the current: (1) charge injection into deep traps within the interior of the oxide; (2) Joule heating of the transistor substrate by hot carriers in the graphene channel; (3) equilibration of interfacial-state filling in response to voltage transients, and; (4) leakage of captured charge from the deep traps, once the pulsed voltage is removed. The time scale associated with these processes ranges from nanoseconds to hours, with process (1) being the fastest and process (4) the slowest. By pulsing the transistors on time intervals as short as a few nanoseconds, we therefore demonstrate how it is possible to obtain output characteristics from them that are essentially free from the influence of these different mechanisms. Under such conditions, the hot-carrier drift velocity is shown to saturate at the large values expected for intrinsic graphene. Beyond graphene, this approach of pulsed characterization of transistor performance should be broadly applicable to studies of other two-dimensional semiconductors, including transition-metal dichalcogenides, black phosphorous, silicene, and topological insulators.
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    Conductance fluctuations in graphene in the presence of long-range disorder
    (2016-03-04)
    Liu, Bobo
    ;
    Akis, Richard
    ;
    Ferry, David K.
    ;
    Bohra, Girish
    ;
    Somphonsane, Ratchanok
    The fluctuations in the conductance of graphene that arise from a long-range disorder potential induced by random impurities are investigated with an atomic tight-binding lattice. The screened impurities lead to a slow variation of the background potential and this varies the overall potential landscape as the Fermi energy or an applied magnetic field is varied. As a result, the phase interference varies randomly and leads to fluctuations in the conductance. Recently, experiments have shown that an applied magnetic field produces a remarkable reduction in the amplitude of these conductance fluctuations. We find qualitative agreement with these experiments, and it appears that the reduction in magnetic field of the fluctuations arises from a field induced smoothing of the conductance landscape.