Sn-Assisted Heteroepitaxy Improves ZnTiN2 Photoabsorbers

John Mangum, Sijia Ke, Melissa Gish, Emily Raulerson, Craig Perkins, Jeffrey Neaton, Andriy Zakutayev, Ann Greenaway

Research output: Contribution to journalArticlepeer-review

1 Scopus Citations


Sustainable production of liquid fuels from abundant resources, such as carbon dioxide and water, may be possible through photoelectrochemical processes. Zinc titanium nitride (ZnTiN2) has been recently demonstrated as a potential photoelectrode semiconductor for photoelectrochemical fuel generation due to its ideal bandgap induced by cation disorder, shared crystal structure with established semiconductors, and self-passivating surface oxides under carbon dioxide reduction operating conditions. However, substantial improvements in crystalline quality and optoelectronic properties of ZnTiN2 are needed to enable such applications. In this work, we investigate the heteroepitaxial growth of ZnTiN2 on c-plane (001) sapphire substrates. Growth on sapphire improves crystal quality, while growth on sapphire at elevated temperatures (300 degrees C) yields highly-oriented, single-crystal-like ZnTiN2 films. When Sn is incorporated during these epitaxial growth conditions, notable improvements in ZnTiN2 film surface roughness and optoelectronic properties are observed. These improvements are attributed to Sn acting as a surfactant during growth and mitigating unintentional impurities such as O and C. The single-crystal-like, 12% Sn-containing ZnTiN2 films exhibit a steep optical absorption onset at the band gap energy around 2 eV, electrical resistivity of 0.7 cm, and a carrier mobility of 0.046 cm2 V-1 s-1 with n-type carrier concentration of 2 x 10^20 cm-3. Density functional theory calculations reveal that moderate substitution of Sn (12.5% of the cation sites) on energetically-preferred cation sites has negligible impact on the optoelectronic properties of cation-disordered ZnTiN2. These results are important steps toward achieving high performance PEC devices based on ZnTiN2 photoelectrodes with efficient photon absorption and photoexcited carrier extraction.
Original languageAmerican English
Pages (from-to)4544-4554
Number of pages11
JournalJournal of Materials Chemistry A
Issue number8
StatePublished - 2024

NREL Publication Number

  • NREL/JA-5K00-87650


  • optoelectronic
  • PEC CO2R
  • photoabsorber
  • surfactant
  • ZnTiN2


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