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Title: Composition dependent valence band order in c-oriented wurtzite AlGaN layers

The valence band order of polar wurtzite aluminum gallium nitride (AlGaN) layers is analyzed for a dense series of samples, grown heteroepitaxially on sapphire substrates, covering the complete composition range. The excitonic transition energies, found by temperature dependent photoluminescence (PL) spectroscopy, were corrected to the unstrained state using input from X-ray diffraction. k∙p theory yields a critical relative aluminum concentration x{sub c}=(0.09±0.05) for the crossing of the uppermost two valence bands for strain free material, shifting to higher values for compressively strained samples, as supported by polarization dependent PL. The analysis of the strain dependent valence band crossing reconciles the findings of other research groups, where sample strain was neglected. We found a bowing for the energy band gap to the valence band with Γ₉ symmetry of b{sub Γ₉}=0.85eV, and propose a possible bowing for the crystal field energy of b{sub cf}=-0.12eV. A comparison of the light extraction efficiency perpendicular and parallel to the c axis of Al{sub x}Ga{sub 1-x}N/Al{sub y}Ga{sub 1-y}N quantum well structures is discussed for different compositions.
Authors:
; ; ; ; ;  [1] ; ; ;  [2] ;  [3]
  1. Institute of Quantum Matter / Semiconductor Physics Group, University of Ulm, Albert-Einstein-Allee 45, 89069 Ulm (Germany)
  2. Institute of Optoelectronics, University of Ulm, Albert-Einstein-Allee 45, 89069 Ulm (Germany)
  3. Institut für Experimentelle Physik, Otto-von-Guericke-Universität Magdeburg, Universitätsplatz 2, 39106 Magdeburg (Germany)
Publication Date:
OSTI Identifier:
22305991
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 116; Journal Issue: 11; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ALUMINIUM COMPOUNDS; CONCENTRATION RATIO; COVERINGS; CRYSTAL FIELD; EFFICIENCY; EXTRACTION; GALLIUM NITRIDES; LAYERS; PHOTOLUMINESCENCE; POLARIZATION; QUANTUM WELLS; SAPPHIRE; SPECTROSCOPY; STRAINS; SUBSTRATES; SYMMETRY; TEMPERATURE DEPENDENCE; VALENCE; VISIBLE RADIATION; X-RAY DIFFRACTION