Browsing by Author "Van De Put, Maarten L."
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Item "Hot Electrons in Si Lose Energy Mostly to Optical Phonons:" Truth or Myth?(American Institute of Physics Inc., 2019-06-05) Fischetti, Massimo V.; Yoder, P. D.; Khatami, Mohammad Mahdi; Gaddemane, Gautam; Van De Put, Maarten L.; 0000-0001-5926-0200 (Fischetti, MV); 0000-0003-0067-8674 (Gaddemane, G); 0000-0001-8014-0350 (Khatami, MM); 0000-0001-9179-6443 (Van de Put, ML); Fischetti, Massimo V.; Khatami, Mohammad Mahdi; Gaddemane, Gautam; Van De Put, Maarten L.Theoretical studies of heat generation and diffusion in Si devices generally assume that hot electrons in Si lose their energy mainly to optical phonons. Here, we briefly review the history of this assumption, and using full-band Monte Carlo simulations - with electron-phonon scattering rates calculated using the rigid-ion approximation and both empirical pseudopotentials and Harris potentials - we show that, instead, electrons lose as much as 2/3 of their energy to acoustic phonons. The scattering rates that we have calculated have been used to study hot-electron effects, such as impact ionization and injection into SiO2, and are in rough agreement with those obtained using density functional theory. Moreover, direct subpicosecond pump-probe experimental results, some of them dating back to 1994, are consistent with the predictions of our model. We conclude that the study of heat generation and dissipation in nanometer-scale Si devices may require a substantial revision of the assumptions that have been considered "common wisdom" so far. © 2019 Author(s).Item Modeling of Electron Transport in Nanoribbon Devices Using Bloch Waves(Institute of Electrical and Electronics Engineers Inc.) Laturia, Akash A.; Van De Put, Maarten L.; Fischetti, Massimo V.; Vandenberghe, William G.; 0000-0001-5926-0200 (Fischetti, MV); 21146635654041982414 (Vandenberghe, WG); Laturia, Akash A.; Van De Put, Maarten L.; Fischetti, Massimo V.; Vandenberghe, William G.One-dimensional (1D) materials present the ultimate limit of extremely scaled devices by virtue of their spatial dimensions and the excellent electrostatic gate control in the transistors based on these materials. Among 1D materials, graphene nanoribbon (a-GNR) prove to be very promising due to high carrier mobility and the prospect of reproducible fabrication process [1]. Two popular approaches to study atomistically the electronic properties expand the wavefunction on either a plane-wave basis set, or through the linear combination of localized atomic orbitals. The use of localized orbitals, especially in the tight-binding (TB) approximation, enables highly scalable numerical implementations. Through continuous improvements in methods and computational capabilities, atomistically describing electronic transport in devices containing more than thousands of atoms has become feasible. Plane waves, while not as scalable, are very popular as the basis of accurate ab-initio software [2]. However, for modeling of transport through larger devices, the computational burden prohibits the direct use of a plane wave basis [3]. Here, we demonstrate a study of the transport characteristics of nanoribbon-based devices using a hybrid approach that combines the benefits of plane waves while retaining the efficiency provided by the TB approximation. © 2018 IEEE.