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Title: Incident wavelength and polarization dependence of spectral shifts in β-Ga 2O 3 UV photoluminescence

Abstract

We report polarization dependent photoluminescence studies on unintentionally-, Mg-, and Ca-doped β-Ga 2O 3 bulk crystals grown by the Czochralski method. In particular, we observe a wavelength shift of the highest-energy UV emission which is dependent on the pump photon energy and polarization. For 240 nm (5.17 eV) excitation almost no shift of the UV emission is observed between E||b and E||c, while a shift of the UV emission centroid is clearly observed for 266 nm (4.66 eV), a photon energy lying between the band absorption onsets for the two polarizations. These results are consistent with UV emission originating from transitions between conduction band electrons and two differentially-populated self-trapped hole (STH) states. Calcuations based on hybrid and self-interaction-corrected density functional theories further validate that the polarization dependence is consistent with the relative stability of two STHs. This observation implies that the STHs form primarily at the oxygen atoms involved in the original photon absorption event, thus providing the connection between incident polarization and emission wavelength. The data imposes a lower bound on the energy separation between the self-trapped hole states of ~70–160 meV, which is supported by the calculations.

Authors:
 [1];  [2];  [3];  [1];  [1];  [1];  [1];  [3]; ORCiD logo [1];  [1]; ORCiD logo [2];  [1];  [1]
  1. Univ. of Utah, Salt Lake City, UT (United States)
  2. Washington State Univ., Pullman, WA (United States)
  3. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA); USDOE Office of Energy Efficiency and Renewable Energy (EERE), Advanced Manufacturing Office (EE-5A); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1497971
Report Number(s):
LLNL-JRNL-760987
Journal ID: ISSN 2045-2322; 949458
Grant/Contract Number:  
AC52-07NA27344; FG02-04ER46148
Resource Type:
Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 8; Journal Issue: 1; Journal ID: ISSN 2045-2322
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Wang, Yunshan, Dickens, Peter T., Varley, Joel B., Ni, Xiaojuan, Lotubai, Emmanuel, Sprawls, Samuel, Liu, Feng, Lordi, Vincenzo, Krishnamoorthy, Sriram, Blair, Steve, Lynn, Kelvin G., Scarpulla, Michael, and Sensale-Rodriguez, Berardi. Incident wavelength and polarization dependence of spectral shifts in β-Ga2O3 UV photoluminescence. United States: N. p., 2018. Web. doi:10.1038/s41598-018-36676-7.
Wang, Yunshan, Dickens, Peter T., Varley, Joel B., Ni, Xiaojuan, Lotubai, Emmanuel, Sprawls, Samuel, Liu, Feng, Lordi, Vincenzo, Krishnamoorthy, Sriram, Blair, Steve, Lynn, Kelvin G., Scarpulla, Michael, & Sensale-Rodriguez, Berardi. Incident wavelength and polarization dependence of spectral shifts in β-Ga2O3 UV photoluminescence. United States. doi:10.1038/s41598-018-36676-7.
Wang, Yunshan, Dickens, Peter T., Varley, Joel B., Ni, Xiaojuan, Lotubai, Emmanuel, Sprawls, Samuel, Liu, Feng, Lordi, Vincenzo, Krishnamoorthy, Sriram, Blair, Steve, Lynn, Kelvin G., Scarpulla, Michael, and Sensale-Rodriguez, Berardi. Mon . "Incident wavelength and polarization dependence of spectral shifts in β-Ga2O3 UV photoluminescence". United States. doi:10.1038/s41598-018-36676-7. https://www.osti.gov/servlets/purl/1497971.
@article{osti_1497971,
title = {Incident wavelength and polarization dependence of spectral shifts in β-Ga2O3 UV photoluminescence},
author = {Wang, Yunshan and Dickens, Peter T. and Varley, Joel B. and Ni, Xiaojuan and Lotubai, Emmanuel and Sprawls, Samuel and Liu, Feng and Lordi, Vincenzo and Krishnamoorthy, Sriram and Blair, Steve and Lynn, Kelvin G. and Scarpulla, Michael and Sensale-Rodriguez, Berardi},
abstractNote = {We report polarization dependent photoluminescence studies on unintentionally-, Mg-, and Ca-doped β-Ga2O3 bulk crystals grown by the Czochralski method. In particular, we observe a wavelength shift of the highest-energy UV emission which is dependent on the pump photon energy and polarization. For 240 nm (5.17 eV) excitation almost no shift of the UV emission is observed between E||b and E||c, while a shift of the UV emission centroid is clearly observed for 266 nm (4.66 eV), a photon energy lying between the band absorption onsets for the two polarizations. These results are consistent with UV emission originating from transitions between conduction band electrons and two differentially-populated self-trapped hole (STH) states. Calcuations based on hybrid and self-interaction-corrected density functional theories further validate that the polarization dependence is consistent with the relative stability of two STHs. This observation implies that the STHs form primarily at the oxygen atoms involved in the original photon absorption event, thus providing the connection between incident polarization and emission wavelength. The data imposes a lower bound on the energy separation between the self-trapped hole states of ~70–160 meV, which is supported by the calculations.},
doi = {10.1038/s41598-018-36676-7},
journal = {Scientific Reports},
number = 1,
volume = 8,
place = {United States},
year = {2018},
month = {12}
}

Journal Article:
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Figures / Tables:

Figure 1 Figure 1: (a) Photograph of the analyzed samples. (b) Absorption spectra for the analyzed samples. Measurements were carried out in flakes exfoliated from the crystals pictured in (a).

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