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Ultrafast Carrier and Lattice Dynamics in Highly Photo-Excited Solids
Albert M.-T. Kim
Ph.D. Thesis, Harvard University, 2001, 199 pages export citation
In this dissertation we report femtosecond
time-resolved measurements of the spectra dielectric
function of amourphous GaAs,GeSb thin films and
single-crystalline Te.
In all materials we measured the evolution of the
dielectric function over a broad energy range (1.7 –3.4
eV), following an impulsive excitation by an ultrashort
laser pulse.
The dielectric function data on a-GaAs show evidence
of a nonthermal, structurally driven
semiconductor-to-metal transition. A comparison to
previously taken dielectric function data on c-GaAs
is especially illuminating in terms of the influence of the
initial structure on the phase transition.
Our results on GeSb thin films reveal a new
nonthermal, metallic phase.The
dielectric function data provide a detailed picture of the
transition from the amorphous phase to the
crystalline phase of these thin films.Furthermore we
refute a previous claim on an ultrafast
disorder-to-order transformation in these materials.
The time-resolved dielectric function data on Te reveal
a great wealth of new information on
impulsively driven coherent phonons, including their in
fluence on the electronic bandstructure.
We find evidence indicative of a new nonthermal phase
of matter which we call a frustrated metal .
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