Optical study of indium phosphate related semiconductor alloys

Lee, Hosun

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https://hdl.handle.net/2142/19020 Copy

Description

Title

Optical study of indium phosphate related semiconductor alloys

Author(s)

Lee, Hosun

Issue Date

1993

Doctoral Committee Chair(s)

Klein, Miles V.

Discipline

Physics

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Condensed Matter Physics
• Optics
• Materials Science Engineering

Language

eng

Abstract

• In this thesis, spectroscopic ellipsometry is used to study the effects of disorder, self-ordering, strain, and dopants on electronic band structure of In$\sb{\rm x}$Ga$\sb{\rm 1-x}$P grown on GaAs, In$\sb{\rm x}$Ga$\sb{\rm 1-x}$P grown on GaP substrate with composition-graded InGaP buffer layer and lattice matched (Al$\sb{\rm x}$Ga$\sb{\rm 1-x}$)$\sb{0.5}$In$\sb{0.5}$P grown on GaAs semiconductor alloys with assistance from measurements of Raman spectroscopy and transmission electron microscopy.
• Our studies of In$\sb{\rm x}$Ga$\sb{\rm 1-x}$P/(GaAs, graded GaP) and (Al$\sb{\rm x}$Ga$\sb{\rm 1-x}$)$\sb {0.5}$In$\sb{0.5}$P/GaAs heteroepitexial layers 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 In$\sb{0.5}$Ga$\sb{0.5}$P/GaAs materials, the amplitudes and peak positions of the signal of the E$\sb1$ critical point decrease as CuPt-type ordering increases whereas the linewidths and phases strongly correlate with dopant concentrations. In contrast, the same properties of E$\sb2$ 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 E$\sb1$ critical point parameters of 1 $\mu$m thick In$\sb{\rm x}$Ga$\sb{\rm 1-x}$P/GaAs (0.4 $\le$ x $\le$ 0.6) as a function of In composition. We observed near cancellation of In composition dependence of the E$\sb1$ peak position by the effect of misfit strain, and also found that the linewidth of the E$\sb1$ 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 E$\sb1$ and E$\sb2$ gaps of (Al$\sb{\rm x}$Ga$\sb{\rm 1-x})\sb{0.5}$In$\sb{0.5}$P/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 between those of the endpoint ternaries, Ga$\sb{0.5}$In$\sb{0.5}$P and Al$\sb{0.5}$In$\sb{0.5}$P.
• There is at present no agreement for In$\sb{\rm x}$Ga$\sb{\rm 1-x}$P alloys on the value of the crossover composition, x$\sb{\rm c}$, of the direct and indirect gaps and whether the L$\sb{\rm 1c}$ must be included among $\Gamma\sb{\rm 1c}$, and X$\sb{\rm 1c}$. The quasi-direct transitions of E$\sb{\rm L1}$ and E$\sb{\rm X3}$ 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 In$\sb{\rm x}$Ga$\sb{\rm 1-x}$P alloys is controversial. Using Raman spectroscopy, we studied the LO phonon-plasmon interaction of the doped In$\sb{0.5}$Ga$\sb{0.5}$P/GaAs alloys and found that one mode behavior is a more appropriate description than two mode behavior.

Type of Resource

text

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Copyright 1993 Lee, Hosun

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