Theoretical studies of high field electron transport in silicon devices
Higman, Jack Mason
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Permalink
https://hdl.handle.net/2142/20148
Description
Title
Theoretical studies of high field electron transport in silicon devices
Author(s)
Higman, Jack Mason
Issue Date
1989
Doctoral Committee Chair(s)
Hess, Karl
Department of Study
Electrical and Computer Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Language
eng
Abstract
In this thesis, the transport of electrons in silicon devices is studied numerically by solving the semiclassical Boltzmann transport equation using the Monte Carlo method. The important cases which are analyzed include both high electric fields and highly inhomogeneous fields. In each of these cases, a reasonably accurate solution of the Boltzmann equation is necessary, including accurate scattering rates and realistic band structure.
A coupled Monte Carlo-Drift Diffusion model for n-MOSFET's is presented which takes advantage of the strengths of both types of calculation. Comparison of the calculated substrate current with experimental values indicates that the model is a valid approach to modeling hot electron effects in n-MOSFET's with effective channel lengths as short as 1 micron.
Another type of semiconductor devices in which impact ionization is an important mechanism is the semiconductor cold cathode electron emitter. Such devices are of considerable technological interest for use as efficient, high current sources of free electrons. Silicon and GaAs p-n electron emitters have been simulated using a single-electron Monte Carlo transport program. The efficiency of the device is calculated as a function of both the work function and the top conducting channel thickness. The potential performance of GaAs devices is explored via the Monte Carlo simulation, and calculated results for the Si device are compared to published experimental data.
The fundamentally nonlocal nature of the impact ionization process, due to its threshold nature, is investigated for the case of a rapidly (spatially) varying electric field. An exponentially increasing electric field is assumed, which is the form appropriate for the longitudinal field in the drain region of an n-MOSFET. The ionization coefficient, which is the quantity that gives the connection between the microscopic process and the macroscopically observable quantities, is calculated. An analytic expression for the ionization coefficient as a function of the electric field is deduced from the spatial variation of the ionization coefficient calculated by Monte Carlo simulations. The expression given here for the electron ionization coefficient depends only on the local electric field and a single length parameter describing the derivative of the field, and therefore can be used to incorporate nonlocal hot electron effects into conventional drift-diffusion device simulators.
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