8,743 research outputs found
Coherent phenomena in semiconductors
A review of coherent phenomena in photoexcited semiconductors is presented.
In particular, two classes of phenomena are considered: On the one hand the
role played by optically-induced phase coherence in the ultrafast spectroscopy
of semiconductors; On the other hand the Coulomb-induced effects on the
coherent optical response of low-dimensional structures.
All the phenomena discussed in the paper are analyzed in terms of a
theoretical framework based on the density-matrix formalism. Due to its
generality, this quantum-kinetic approach allows a realistic description of
coherent as well as incoherent, i.e. phase-breaking, processes, thus providing
quantitative information on the coupled ---coherent vs. incoherent--- carrier
dynamics in photoexcited semiconductors.
The primary goal of the paper is to discuss the concept of quantum-mechanical
phase coherence as well as its relevance and implications on semiconductor
physics and technology. In particular, we will discuss the dominant role played
by optically induced phase coherence on the process of carrier photogeneration
and relaxation in bulk systems. We will then review typical field-induced
coherent phenomena in semiconductor superlattices such as Bloch oscillations
and Wannier-Stark localization. Finally, we will discuss the dominant role
played by Coulomb correlation on the linear and non-linear optical spectra of
realistic quantum-wire structures.Comment: Topical review in Semiconductor Science and Technology (in press)
(Some of the figures are not available in electronic form
Theory of spin-polarized transport in semiconductor heterojunctions: Proposal for spin injection and detection in silicon
Spin injection and detection in silicon is a difficult problem, in part
because the weak spin-orbit coupling and indirect gap preclude using standard
optical techniques. We propose two ways to overcome this difficulty, and
illustrate their operation by developing a model for spin-polarized transport
across a heterojunction. We find that equilibrium spin polarization of holes
leads to a strong modification of the spin and charge dynamics of electrons,
and we show how the symmetry properties of the charge current can be exploited
to detect spin injection in silicon using currently available techniques.Comment: 4 pages, 4 figures, added footnot
Self-sustained current oscillations in the kinetic theory of semiconductor superlattices
We present the first numerical solutions of a kinetic theory description of
self-sustained current oscillations in n-doped semiconductor superlattices. The
governing equation is a single-miniband Boltzmann-Poisson transport equation
with a BGK (Bhatnagar-Gross-Krook) collision term. Appropriate boundary
conditions for the distribution function describe electron injection in the
contact regions. These conditions seamlessly become Ohm's law at the injecting
contact and the zero charge boundary condition at the receiving contact when
integrated over the wave vector. The time-dependent model is numerically solved
for the distribution function by using the deterministic Weighted Particle
Method. Numerical simulations are used to ascertain the convergence of the
method. The numerical results confirm the validity of the Chapman-Enskog
perturbation method used previously to derive generalized drift-diffusion
equations for high electric fields because they agree very well with numerical
solutions thereof.Comment: 26 pages, 16 figures, to appear in J. Comput. Phy
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