Isotope analysis of diamond-surface passivation effect of high-temperature H<inf>2</inf>O-grown atomic layer deposition-Al<inf>2</inf>O<inf>3</inf> films

Atsushi Hiraiwa, Tatsuya Saito, Daisuke Matsumura, Hiroshi Kawarada

    Research output: Contribution to journalArticle

    10 Citations (Scopus)

    Abstract

    The Al<inf>2</inf>O<inf>3</inf> film formed using an atomic layer deposition (ALD) method with trimethylaluminum as Al precursor and H<inf>2</inf>O as oxidant at a high temperature (450-°C) effectively passivates the p-type surface conduction (SC) layer specific to a hydrogen-terminated diamond surface, leading to a successful operation of diamond SC field-effect transistors at 400-°C. In order to investigate this excellent passivation effect, we carried out an isotope analysis using D<inf>2</inf>O instead of H<inf>2</inf>O in the ALD and found that the Al<inf>2</inf>O<inf>3</inf> film formed at a conventional temperature (100-°C) incorporates 50 times more CH<inf>3</inf> groups than the high-temperature film. This CH<inf>3</inf> is supposed to dissociate from the film when heated afterwards at a higher temperature (550-°C) and causes peeling patterns on the H-terminated surface. The high-temperature film is free from this problem and has the largest mass density and dielectric constant among those investigated in this study. The isotope analysis also unveiled a relatively active H-exchange reaction between the diamond H-termination and H<inf>2</inf>O oxidant during the high-temperature ALD, the SC still being kept intact. This dynamic and yet steady H termination is realized by the suppressed oxidation due to the endothermic reaction with H<inf>2</inf>O. Additionally, we not only observed the kinetic isotope effect in the form of reduced growth rate of D<inf>2</inf>O-oxidant ALD but found that the mass density and dielectric constant of D<inf>2</inf>O-grown Al<inf>2</inf>O<inf>3</inf> films are smaller than those of H<inf>2</inf>O-grown films. This is a new type of isotope effect, which is not caused by the presence of isotopes in the films unlike the traditional isotope effects that originate from the presence of isotopes itself. Hence, the high-temperature ALD is very effective in forming Al<inf>2</inf>O<inf>3</inf> films as a passivation and/or gate-insulation layer of high-temperature-operation diamond SC devices, and the knowledge of the aforementioned new isotope effect will be a basis for further enhancing ALD technologies in general.

    Original languageEnglish
    Article number215304
    JournalJournal of Applied Physics
    Volume117
    Issue number21
    DOIs
    Publication statusPublished - 2015 Jun 7

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    atomic layer epitaxy
    passivity
    isotopes
    diamonds
    isotope effect
    conduction
    permittivity
    endothermic reactions
    peeling
    insulation
    field effect transistors
    oxidation
    causes
    kinetics
    hydrogen

    ASJC Scopus subject areas

    • Physics and Astronomy(all)

    Cite this

    Isotope analysis of diamond-surface passivation effect of high-temperature H<inf>2</inf>O-grown atomic layer deposition-Al<inf>2</inf>O<inf>3</inf> films. / Hiraiwa, Atsushi; Saito, Tatsuya; Matsumura, Daisuke; Kawarada, Hiroshi.

    In: Journal of Applied Physics, Vol. 117, No. 21, 215304, 07.06.2015.

    Research output: Contribution to journalArticle

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    abstract = "The Al2O3 film formed using an atomic layer deposition (ALD) method with trimethylaluminum as Al precursor and H2O as oxidant at a high temperature (450-°C) effectively passivates the p-type surface conduction (SC) layer specific to a hydrogen-terminated diamond surface, leading to a successful operation of diamond SC field-effect transistors at 400-°C. In order to investigate this excellent passivation effect, we carried out an isotope analysis using D2O instead of H2O in the ALD and found that the Al2O3 film formed at a conventional temperature (100-°C) incorporates 50 times more CH3 groups than the high-temperature film. This CH3 is supposed to dissociate from the film when heated afterwards at a higher temperature (550-°C) and causes peeling patterns on the H-terminated surface. The high-temperature film is free from this problem and has the largest mass density and dielectric constant among those investigated in this study. The isotope analysis also unveiled a relatively active H-exchange reaction between the diamond H-termination and H2O oxidant during the high-temperature ALD, the SC still being kept intact. This dynamic and yet steady H termination is realized by the suppressed oxidation due to the endothermic reaction with H2O. Additionally, we not only observed the kinetic isotope effect in the form of reduced growth rate of D2O-oxidant ALD but found that the mass density and dielectric constant of D2O-grown Al2O3 films are smaller than those of H2O-grown films. This is a new type of isotope effect, which is not caused by the presence of isotopes in the films unlike the traditional isotope effects that originate from the presence of isotopes itself. Hence, the high-temperature ALD is very effective in forming Al2O3 films as a passivation and/or gate-insulation layer of high-temperature-operation diamond SC devices, and the knowledge of the aforementioned new isotope effect will be a basis for further enhancing ALD technologies in general.",
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