% abstract for the KB-II Seminar in Dresden 2002

\documentclass[12pt]{article}

\begin{document}
\thispagestyle{empty}

\title{ Full-band approach to impact ionization and high-field 
        transport in semiconductors }

\author{ A.\ Kuligk, N.\ Fitzer, and R.\ Redmer \\
 Fachbereich Physik, Universit\"at Rostock,
 D-18051 Rostock }
\date{}
\maketitle

Impact ionization plays a crucial role for electron transport in wide
band\-gap semiconductor materials such as ZnS, GaN, and SrS at high
electric fields. Appropriate quantum kinetic equations for high field
electron transport in semiconductors can be derived within the
framework of Greens function technique or, alternatively, within
response theory. The electron-electron collision integral for the
inelastic process of impact ionization has been evaluated considering
high-field quantum corrections such as the intracollisional field
effect [1] and collisional broadening [2]. A pronounced 
softening of the impact ionization threshold is obtained.

Besides high-field and quantum effects, the use of a realistic band
structure is essential for the determination of the microscopic
scattering rate. Band structure calculations are usually performed
within the empirical pseudopotential method (EPM). We present {\it
  ab initio} band structures for the wide bandgap materials ZnS, GaN,
and SrS derived from density functional theory in local density
approximation using an exact exchange functional (EXX-LDA), see [3].

The field dependent impact ionization rates are included in full-band
ensemble Monte Carlo simulations of high-field electron transport.
Although the impact ionization rate itself is strongly effected,
little effect is observed on measurable quantities such as the impact
ionization coefficient or the electron distribution function itself.
Results for the drift velocity and the mean kinetic energy dependent
on the field strength are also shown.\\

[1] R.~Redmer {\it et al.}, 
    J.\ Appl.\ Phys.\ {\bf 87}, 781 (2000).

[2] J.R.~Madureira {\it et al.}, 
    J.\ Appl.\ Phys.\ {\bf 90}, 829 (2002).

[3] M.~St\"adele {\it et al.},  
    Phys.\ Rev.\ Lett. {\bf 79}, 2089 (1997)

\end{document}






