Electrical effect of introducing elemental sodium into the Bridgman melt of CuInSe2+x crystals

Transport and other measurements have been made on CuInSe2+x samples obtained from Bridgman ingots grown from melts containing controlled amounts of elemental sodium, where x represents the excess of Se over stoichiometry. Thermoelectric power and Hall coefficient at room temperature show a conducti...

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Bibliographic Details
Published in:Journal of crystal growth 2014-02, Vol.387, p.36-40
Main Authors: Myers, Hadley F., Champness, Clifford H., Shih, Ishiang
Format: Article
Language:English
Subjects:
A1. X-ray diffraction
A2. Bridgman technique
A3. Single-crystal growth
Applied sciences
B2. Semiconducting ternary compounds
B3. Solar Cells
Bridgman method
CHALCOPYRITE
Condensed matter: structure, mechanical and thermal properties
COPPER INDIUM SELENIDE
Cross-disciplinary physics: materials science
rheology
CRYSTAL GROWTH
Crystals
Electric power generation
ELECTRICAL CONDUCTIVITY
ELECTRICITY
Energy
Exact sciences and technology
Growth from melts
zone melting and refining
Materials science
Melts (crystal growth)
Methods of crystal growth
physics of crystal growth
Natural energy
Photovoltaic conversion
Physics
Sodium
Solar cells. Photoelectrochemical cells
Solar energy
Structure of solids and liquids
crystallography
Structure of specific crystalline solids
Theory and models of crystal growth
physics of crystal growth, crystal morphology and orientation
Thermoelectricity
X RAY SPECTROSCOPY
X-ray photoelectron spectroscopy
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Summary:Transport and other measurements have been made on CuInSe2+x samples obtained from Bridgman ingots grown from melts containing controlled amounts of elemental sodium, where x represents the excess of Se over stoichiometry. Thermoelectric power and Hall coefficient at room temperature show a conductivity sign change from p- to n-type in otherwise stoichiometric CuInSe2 (x=0), with added Na between 0.2 and 0.3at%. It is further found that the critical amount of Na required to change the conductivity type, denoted by [Na]crit, increases with x, almost linearly, with an initial slope of 2, corresponding to an approximate formula of [Na]crit=2x+δ, where δ is found to be 0.25at% Na. This behavior can be accounted for quantitatively using a ‘selenium starvation’ model, whereby at the p-to-n type change, two atoms of sodium have reacted with one atom of Se to form a molecule like Na2Se, with an atom-to-atom ratio [Na]/[Se]=2. Such molecules were detected in growth run residues. However, no Na or Na compounds were detected in the interior of bulk crystals. In stoichiometric material (x=0), the crystal structure remained chalcopyrite with up to at least 3at% Na in the melt, despite the conductivity type changes. Further, no β-phase was detected in the bulk material by XRD but it was found at the surface of samples by XPS. •Bulk CuInSe2 was grown by a Bridgman-method with varying amounts of elemental Na and excess Se.•Na changed the conductivity of the CuInSe2 from p- to n-type by Seebeck and Hall measurements.•This type change was mitigated with excess Se, so that more Na was needed for the change to occur.•A Se-starvation interaction model between the Na and Se to explain the mechanism responsible.
ISSN:0022-0248
1873-5002
DOI:10.1016/j.jcrysgro.2013.10.038