Single-crystalline Cu2O thin films of optical quality as obtained by the oxidation of single-crystal Cu thin films at low temperature

Taewoo Ha, Inhee Park, Kyung Ik Sim, Howon Lee, Jong Sung Bae, Su Jae Kim, Jong Phil Kim, Teun Teun Kim, Jae Hoon Kim, Joon Ik Jang, Se Young Jeong

Research output: Contribution to journalArticle

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Abstract

High-quality, single-crystal-like Cu2O thin films of various thicknesses (10 nm-45 nm) were prepared at a low temperature (150 °C) by controlling layer-by-layer oxidation of wafer-scale Cu thin films sputtered along the (111) direction using a pure single-crystal Cu target. The cross-sectional images of the thin films reveal high crystallinity of Cu2O layers except for 60° twinning in the sequential stacking order as evidenced by high-resolution transmission electron microscopy, which is consistent with the absence of the photoluminescence (PL) signals arising from atomic-scale vacancies. The optical properties of our Cu2O films were investigated using temperature-dependent PL and Raman spectroscopy. All of the Cu2O thin films exhibit characteristic band-to-band transitions together with the series of yellow excitonic transitions slightly below the fundamental bandgap. The spectral locations for the PL are approximately consistent with those for the bulk counterpart. The excellent optical quality of our Cu2O was further demonstrated by significantly reduced quasi-direct transition that occurs at symmetry-breaking crystal imperfection, which relaxes the stringent momentum conservation rule. We identified the three main Raman scattering modes of the Cu2O thin films, where the two forbidden modes of Γ15(1) and Γ12-+Γ25- are resonantly allowed by the proximity of the incident photon energy to the green bandgap. We believe that our synthesis technique can be utilized for the preparation of single-crystal-like metal oxide thin films at low production temperatures with precise thickness control for the development of novel optoelectronic devices and for the exploration of the nanoscale light-matter interaction as well.

Original languageEnglish
Article number031115
JournalAPL Materials
Volume7
Issue number3
DOIs
Publication statusPublished - 2019 Mar 1

Fingerprint

Single crystals
Crystalline materials
Thin films
Oxidation
Temperature
Low temperature production
Photoluminescence
Energy gap
Thickness control
Photoluminescence spectroscopy
Twinning
Crystal symmetry
Electron transitions
High resolution transmission electron microscopy
Optoelectronic devices
Oxide films
Vacancies
Raman spectroscopy
Raman scattering
Conservation

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Engineering(all)

Cite this

Ha, Taewoo ; Park, Inhee ; Sim, Kyung Ik ; Lee, Howon ; Bae, Jong Sung ; Kim, Su Jae ; Kim, Jong Phil ; Kim, Teun Teun ; Kim, Jae Hoon ; Jang, Joon Ik ; Jeong, Se Young. / Single-crystalline Cu2O thin films of optical quality as obtained by the oxidation of single-crystal Cu thin films at low temperature. In: APL Materials. 2019 ; Vol. 7, No. 3.
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abstract = "High-quality, single-crystal-like Cu2O thin films of various thicknesses (10 nm-45 nm) were prepared at a low temperature (150 °C) by controlling layer-by-layer oxidation of wafer-scale Cu thin films sputtered along the (111) direction using a pure single-crystal Cu target. The cross-sectional images of the thin films reveal high crystallinity of Cu2O layers except for 60° twinning in the sequential stacking order as evidenced by high-resolution transmission electron microscopy, which is consistent with the absence of the photoluminescence (PL) signals arising from atomic-scale vacancies. The optical properties of our Cu2O films were investigated using temperature-dependent PL and Raman spectroscopy. All of the Cu2O thin films exhibit characteristic band-to-band transitions together with the series of yellow excitonic transitions slightly below the fundamental bandgap. The spectral locations for the PL are approximately consistent with those for the bulk counterpart. The excellent optical quality of our Cu2O was further demonstrated by significantly reduced quasi-direct transition that occurs at symmetry-breaking crystal imperfection, which relaxes the stringent momentum conservation rule. We identified the three main Raman scattering modes of the Cu2O thin films, where the two forbidden modes of Γ15(1) and Γ12-+Γ25- are resonantly allowed by the proximity of the incident photon energy to the green bandgap. We believe that our synthesis technique can be utilized for the preparation of single-crystal-like metal oxide thin films at low production temperatures with precise thickness control for the development of novel optoelectronic devices and for the exploration of the nanoscale light-matter interaction as well.",
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Single-crystalline Cu2O thin films of optical quality as obtained by the oxidation of single-crystal Cu thin films at low temperature. / Ha, Taewoo; Park, Inhee; Sim, Kyung Ik; Lee, Howon; Bae, Jong Sung; Kim, Su Jae; Kim, Jong Phil; Kim, Teun Teun; Kim, Jae Hoon; Jang, Joon Ik; Jeong, Se Young.

In: APL Materials, Vol. 7, No. 3, 031115, 01.03.2019.

Research output: Contribution to journalArticle

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AU - Ha, Taewoo

AU - Park, Inhee

AU - Sim, Kyung Ik

AU - Lee, Howon

AU - Bae, Jong Sung

AU - Kim, Su Jae

AU - Kim, Jong Phil

AU - Kim, Teun Teun

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AU - Jang, Joon Ik

AU - Jeong, Se Young

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