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Title: Phonon dynamics and Urbach energy studies of MgZnO alloys

The Mg{sub x}Zn{sub 1−x}O alloy system is emerging as an environmentally friendly choice in ultraviolet lighting and sensor technologies. Knowledge of defects which impact their optical and material properties is a key issue for utilization of these alloys in various technologies. The impact of phase segregation, structural imperfections, and alloy inhomogeneities on the phonon dynamics and electronic states of Mg{sub x}Zn{sub 1−x}O thin films were studied via selective resonant Raman scattering (SRRS) and Urbach analyses, respectively. A series of samples with Mg composition from 0–68% were grown using a sputtering technique, and the optical gaps were found to span a wide UV range of 3.2–5.8 eV. The extent of the inherent phase segregation was determined via SRRS using two UV-laser lines to achieve resonance with the differing optical gaps of the embedded cubic and wurtzite structural domains. The occurrence of Raman scattering from cubic structures is discussed in terms of relaxation of the selection rules due to symmetry breaking by atomic substitutions. The Raman linewidth and Urbach energy behavior indicate the phase segregation region occurs in the range of 47–66% Mg. Below the phase segregation, the longitudinal optical phonons are found to follow the model of one-mode behavior. The phonon decaymore » model of Balkanski et al. indicates that the major contributor to Raman linewidth arises from the temperature-independent term attributed to structural defects and alloy inhomogeneity, while the contribution from anharmonic decay is relatively small. Moreover, a good correlation between Urbach energy and Raman linewidth was found, implying that the underlying crystal dynamics affecting the phonons also affect the electronic states. Furthermore, for alloys with low Mg composition structural defects are dominant in determining the alloy properties, while at higher compositions alloy inhomogeneity cannot be neglected.« less
Authors:
; ; ; ;  [1] ;  [2]
  1. Department of Physics, University of Idaho, Moscow, Idaho 83844-0903 (United States)
  2. Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164-2814 (United States)
Publication Date:
OSTI Identifier:
22399360
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 12; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CONCENTRATION RATIO; CORRELATIONS; CRYSTALS; CUBIC LATTICES; EV RANGE; MAGNESIUM COMPOUNDS; PHONONS; RAMAN EFFECT; RELAXATION; SEGREGATION; SELECTION RULES; SYMMETRY BREAKING; TERNARY ALLOY SYSTEMS; THIN FILMS; ULTRAVIOLET RADIATION; ZINC OXIDES