Optical study of InP related semiconductor alloys;spectroscopic ellipsometry
Lee, Hosun
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https://hdl.handle.net/2142/18866
Description
Title
Optical study of InP related semiconductor alloys;spectroscopic ellipsometry
Author(s)
Lee, Hosun
Issue Date
1993-10
Doctoral Committee Chair(s)
Klein, Miles V.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
optical physics
InP
semiconductor alloys
Language
en
Abstract
In this thesis, spectroscopic ellipsometry is used to study the effects of disorder,
self-ordering, strain, and dopants on electronic band structure of InxGal-xP grown on
GaAs, InxGa1_xP grown on GaP substrate with composition-graded InGaP buffer layer
and lattice matched (AlxGa1_x)o.sino.sP grown on GaAs semiconductor alloys with
assistance from measurements of Raman spectroscopy and transmission electron
microscopy.
Our studies of InxGal-xP/(GaAs, graded GaP) and (AlxGal-x)o.sino.sP/GaAs
heteroepitexiallayers principally demonstrate the efficacy of using spectroscopic
ellipsometry to probe the modulations of critical points, the high symmetry points of
electronic band structure, which are caused by long( or short) range ordering, misfit strain,
defects, or dopants. For example, in the case of ordered and doped Ino.sGao.sP/GaAs
materials, the amplitudes and peak positions of the signal of the E1 critical point decrease
as CuPt-type ordering increases whereas the linewidths and phases strongly correlate with
dopant concentrations. In contrast, the same properties of E2 critical points decrease as
CuPt-type ordering increases. We attribute this ordering dependent correlation of critical
point parameters to the formation of a spontaneous (111) InP/GaP superlattice. We also
studied the effect of misfit strain on the E1 critical point parameters of 1 ~m thick
InxGal-xP/GaAs (0.4~~0.6) as a function of In composition. We observed near
cancellation of In composition dependence of the E1 peak position by the effect of misfitstrain,
and also found that the linewidth of the E1 peak broadens rapidly in those
compositions under tensile stress even below the critical thickness, where elastic energy
originating from misfit strain relaxes generating defects, e. g. microcracks. Finally, the
investigation of the critical points of the E1 and E2 gaps of (AlxGal-x)o.sino.sP/GaAs
leads to the conclusion that the electronic charge distributions of Ga-P and Al-P bonds
may be similar because their critical point parameters linearly interpolate bet•ween those
of the endpoint ternaries, Gao.sino.sP and Alo.sino.sP.
There is at present no agreement for InxGal-xP alloys on the value of the crossover
composition, Xc, of the direct and indirect gaps and whether the L1c must be included
among f'1c and Xlc· The quasi-direct transitions ofEu and Ex3 observed by ellipsometry
favor the two conduction band model. We also discuss the origin of the quasi-direct
transitions. In addition, the mode behavior of optic phonons in the InxGa1_xP alloys is
controversial. Using Raman spectroscopy, we studied the LO phonon-plasmon
interaction of the doped Ino.sGao.sP/GaAs alloys and found that one mode behavior is a
more appropriate description than two mode behavior.
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