skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Phonon dynamics and Urbach energy studies of MgZnO alloys

; ; ; ; ORCiD logo;
Publication Date:
Sponsoring Org.:
OSTI Identifier:
Grant/Contract Number:
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Journal of Applied Physics
Additional Journal Information:
Journal Volume: 117; Journal Issue: 12; Related Information: CHORUS Timestamp: 2016-12-21 06:54:47; Journal ID: ISSN 0021-8979
American Institute of Physics
Country of Publication:
United States

Citation Formats

Huso, Jesse, Che, Hui, Thapa, Dinesh, Canul, Amrah, McCluskey, M. D., and Bergman, Leah. Phonon dynamics and Urbach energy studies of MgZnO alloys. United States: N. p., 2015. Web. doi:10.1063/1.4916096.
Huso, Jesse, Che, Hui, Thapa, Dinesh, Canul, Amrah, McCluskey, M. D., & Bergman, Leah. Phonon dynamics and Urbach energy studies of MgZnO alloys. United States. doi:10.1063/1.4916096.
Huso, Jesse, Che, Hui, Thapa, Dinesh, Canul, Amrah, McCluskey, M. D., and Bergman, Leah. 2015. "Phonon dynamics and Urbach energy studies of MgZnO alloys". United States. doi:10.1063/1.4916096.
title = {Phonon dynamics and Urbach energy studies of MgZnO alloys},
author = {Huso, Jesse and Che, Hui and Thapa, Dinesh and Canul, Amrah and McCluskey, M. D. and Bergman, Leah},
abstractNote = {},
doi = {10.1063/1.4916096},
journal = {Journal of Applied Physics},
number = 12,
volume = 117,
place = {United States},
year = 2015,
month = 3

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1063/1.4916096

Citation Metrics:
Cited by: 6works
Citation information provided by
Web of Science

Save / Share:
  • 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 amore » 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 decay 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
  • Highlights: • Comparison of group-I elements doped ZnO nanoparticles and thin films. • Calculation of electron–phonon coupling and phonon lifetime from Raman spectroscopy. • Estimation of interband states from Urbach energy. - Abstract: Group-I (Li, Na, K & Cs) elements doped ZnO nanoparticles (NPs) and thin films were prepared using sol–gel method. XRD data and TEM images confirm the absence of any other secondary phase different from wurtzite type ZnO. Spherical shapes of grains are observed from the surfaces of doped ZnO films by atomic force microscope images (AFM) and presences of dopants are confirmed from energy dispersive X-ray spectra.more » The Raman active E{sub 2} (high), E{sub 2} (low), E{sub 1} and A{sub 1} (LO) modes are observed from both ZnO NPs and thin films. First-order longitudinal optical (LO) phonon is found to have contributions from direct band transition and localized excitons. Electron–phonon coupling, phonon lifetime and deformation energy of ZnO are calculated based on the effect of dopants with respect to the multiple Raman LO phonon scattering. Presence of localized interbands states in doped ZnO NPs and thin films are found from the Urbach energy calculations.« less
  • The characteristics of the excitonic absorption and emission around the fundamental bandgap of wurtzite Mg{sub x}Zn{sub 1-x}O grown on c-plane sapphire substrates by plasma assisted molecular beam epitaxy with Mg contents between x = 0 and x = 0.23 are studied using spectroscopic ellipsometry and photoluminescence (PL) measurements. The ellipsometric data were analyzed using a multilayer model yielding the dielectric function (DF). The imaginary part of the DF for the alloys exhibits a pronounced feature which is attributed to exciton-phonon coupling (EPC) similar to the previously reported results for ZnO. Thus, in order to determine reliable transition energies, the spectralmore » dependence is analyzed by a model which includes free excitonic lines, the exciton continuum, and the enhanced absorption due to EPC. A line shape analysis of the temperature-dependent PL spectra yielded in particular the emission-related free excitonic transition energies, which are compared to the results from the DF line-shape analysis. The PL linewidth is discussed within the framework of an alloy disorder model.« less
  • We report on bandgap bowing parameters for wurtzite and cubic MgZnO alloys from a study of high quality and single phase films in all Mg content range. The Mg contents in the MgZnO films were accurately determined using the energy dispersive spectrometer and X-ray photoelectron spectroscopy (XPS). The measurement of bandgap energies by examining the onset of inelastic energy loss in core-level atomic spectra from XPS is proved to be valid for determining the bandgap of MgZnO films. The dependence of the energy bandgap on Mg content is found to deviate downwards from linearity. Fitting of the bandgap data resultedmore » in two bowing parameters of 2.01 ± 0.04 eV and 1.48 ± 0.11 eV corresponding to wurtzite and cubic MgZnO films, respectively.« less
  • We present numerical simulations for the acoustic-phonon-limited mobility, μ{sub ac}, in two-dimensional electron gases (2DEGs) confined in MgZnO/ZnO heterostructures for temperatures 0.4–20 K. The calculations are based on the semiclassical Boltzmann equation. We examine two 2DEGs with sheet densities 1.4 and 7×10{sup 15} m{sup −2}. Good agreement is found with recent experimental data without any adjustable parameter. We also calculate the contribution to thermopower that arises due to the phonon wind set up by a temperature gradient (the so-called phonon-drag thermopower, S{sup g}). A giant magnitude of S{sup g} is predicted that exceeds 50–100 mV/K at 5 K depending onmore » the sheet density. Our findings suggest that the ZnO based heterostructures could be promising materials for thermoelectric applications at low temperatures.« less