Browsing by Subject "Impact ionization"
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Item Open Access Electron initiated impact ionization in AlGaN alloys(Institute of Physics, 2002) Bulutay, C.Detailed impact ionization (II) analysis of electrons is presented for AlGaN alloys as a vital resource for solar-blind avalanche photodiode and high power transistor applications. Necessary ingredients for the II characterization are supplied from a recent experiment on the GaN end, and a Keldysh analysis for the AlN end, of the alloy AlGaN. High-field electron dynamics are simulated using an ensemble Monte Carlo framework, accounting for all valleys in the lowest two conduction bands, obtained from accurate empirical pseudopotential band structure computations. The effect of alloy scattering on II is considered and observed to be significant. For any AlxGa1-xN alloy, the electron II coefficients are found to obey the form, A exp(-K/F), for the electric field, F.Item Open Access Elements of nanocrystal high-field carrier transport modeling(Wiley, 2007) Sevik, Cem; Bulutay, CeyhunEmbedded semiconductor nanocrystals (NCs) within wide bandgap oxide materials are being considered for light emission and solar cell applications. One of the fundamental issues is the high-field transport in NCs. This requires the combination of a number of tools: ensemble Monte Carlo carrier transport simulation, ab initio band structure of the bulk oxide, Fermi's golden rule modeling of impact ionization and Auger processes and the pseudopotential-based atomistic description of the confined NC states. These elements are outlined in this brief report.Item Open Access Gunn oscillations in GaN channels(IOP, 2004) Sevik, Cem; Bulutay, CeyhunGallium nitride with its high negative differential mobility threshold is an appealing material for high power millimetre-wave oscillators as a Gunn diode. By means of extensive ensemble Monte Carlo simulations, the dynamics of large-amplitude Gunn domain oscillations from 120 GHz to 650 GHz is studied in detail. Their operations are checked under both impressed single-tone sinusoidal bias and external tank circuit conditions. The width of the doping notch is observed to enhance higher harmonic efficiency at the expense of the fundamental frequency up to a critical value, beyond which sustained Gunn oscillations cease. The degeneracy effects due to the Pauli exclusion principle are also considered, but their effects are seen to be negligible within the realistic bounds of the Gunn diode operation.