Evidence for a phase transition of β-gallium oxide at very low oxygen pressures

Maximilian Fleischer, Leo Höllbauer, Eberhard Born, Hans Meixner

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

Depending on the operating temperature, gas sensors that are based on n-type-semiconductor, polycrystalline gallium oxide (Ga2O3) thin films are used to detect oxygen (at temperatures, T, of ≥ 850°C) or reducing gases (T ≤ 900°C). At high temperatures (T ≥ 900°C), β-Ga2O3 has an oxygen deficiency in the crystal lattice that is in dynamic equilibrium with the oxygen in the surrounding atmosphere. Variations in the conductivity of the sensor are caused by variations of the concentration of ionized oxygen vacancies. Therefore, a reduction in the proportion of oxygen or an increase in the concentration of reducing gases in the atmosphere in which the sensor is located leads to an increasing number of conducting electrons and, hence, an increasing conductivity. During a research project to investigate the long-term stability of thin β-Ga2O3 films in a variety of strongly reducing atmospheres at T > 600°C, a previously unknown phenomenon has been observed when measurements on low oxygen partial pressures (pO2 ≤ 10-10 Pa (≤ 10-15 bar)) have been made. A sharp decrease in sensor conductivity, by several orders of magnitude, is observed each time when pO2 is reduced to a value of <10-15 bar at temperatures in the range of ∼750°-1000°C. The reason for this may be a phase transition in the β-Ga2O3 layer. However, attempts to freeze the new state with subsequent identification by X-ray diffractometry have not succeeded in identifying the new phase.

Original languageEnglish
Pages (from-to)2121-2125
Number of pages5
JournalJournal of the American Ceramic Society
Volume80
Issue number8
Publication statusPublished - Aug 1 1997

ASJC Scopus subject areas

  • Ceramics and Composites
  • Materials Chemistry

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