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Title:{112} Polar Surfaces of Copper(indium,gallium)selenide: Properties and Effects on Crystal Growth
Author(s):Liao, Dongxiang
Doctoral Committee Chair(s):Rockett, Angus A.
Department / Program:Materials Science and Engineering
Discipline:Materials Science and Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Engineering, Materials Science
Abstract:Cu(In,Ga)Se2 (GIGS) are promising materials for thin film photovoltaic applications. This work studies the epitaxial growth of CIGS single crystal films on GaAs substrates of various orientations and characterizes the properties of the thin films. A surprising finding is the strong tendency of film surfaces to facet to {112} planes. The work attempted to establish the connections between the film morphology, the surface energies, the surface chemical compositions, and the reconstruction of polar surfaces. Using angle-resolved photoelectron emission spectroscopy, I found that there is a severe Cu depletion at the first 1--2 layer of the free surface of CuInSe2 and the surface is semiconducting. The results strongly support the model of a reconstructed non-stoichiometric polar surface and exclude the previously believed existence of a bulk second phase on the CIS surface. Unique features of the film morphology suggest that the properties and structure of the polar surfaces have great effects on the growth of the crystals, and probably on the incorporation of the large amount of point defects. Measured chemical composition profiles indicate that the Cu depletion observed on free CIGS surface remains at the CIGS/CdS heterojunction interface and Cd is incorporated into the surface of CIGS. It is proposed that this non-stoichiometric composition leads to charge imbalance at the interface and causes the type-inversion of the CIGS surface, which are favorable for the device performance.
Issue Date:2003
Description:71 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2003.
Other Identifier(s):(MiAaPQ)AAI3101902
Date Available in IDEALS:2015-09-25
Date Deposited:2003

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