Effect of thickness and carrier density on the optical polarization of Al0.44Ga0.56N/Al0.55Ga0.45N quantum well layers

The thickness and carrier density of AlGaN quantum well (QW) layers have a strong influence on the valence subband structure, and the resulting optical polarization and light extraction of ultraviolet light-emitting diodes. An ultraviolet-emitting (270–280 nm) multiple quantum well heterostructure c...

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Bibliographic Details
Published in:Journal of applied physics 2014-05, Vol.115 (17)
Main Authors: Wierer, J. J., Montaño, I., Crawford, M. H., Allerman, A. A.
Format: Article
Language:English
Subjects:
Applied physics
Carrier density
Conduction bands
Emitters
Heterostructures
Optical polarization
Organic light emitting diodes
Quantum wells
Thickness
Ultraviolet radiation
Valence band
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Summary:The thickness and carrier density of AlGaN quantum well (QW) layers have a strong influence on the valence subband structure, and the resulting optical polarization and light extraction of ultraviolet light-emitting diodes. An ultraviolet-emitting (270–280 nm) multiple quantum well heterostructure consisting of 3 periods of Al0.44Ga0.56N/Al0.55Ga0.45N with individual layer thicknesses between 2–3.2 nm is studied both experimentally and theoretically. The optical polarization changes to preferentially polarized perpendicular to the QW plane as the QW thickness increases or the carrier density increases. Calculations show these trends are due to (a) a larger decrease in overlap of conduction band to light and heavy hole envelope functions compared to crystal-field split-off envelope functions, and (b) coupling between the valence subbands where higher heavy hole subbands couple to lower light hole and crystal-field split-off subbands. These changes in the valence band have a profound effect on the optical polarization, emission patterns, and eventual light extraction for ultraviolet emitters at these compositions and thicknesses, and need to be controlled to ensure high device efficiency.
ISSN:0021-8979
1089-7550
DOI:10.1063/1.4874739