Hildebrandt, Erwin Matti (2012)
Oxygen Engineered Hafnium Oxide Thin Films grown by Reactive Molecular Beam Epitaxy.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung
Kurzbeschreibung (Abstract)
This study applies RMBE to grow thin films of hafnium oxide, a widely studied material which has found its way into commercialisation as a replacement of SiO2 in a field effect transistor. After investigating different substrates and probing various deposition conditions, RMBE-grown films of hafnium oxide yielded to epitaxial films of hafnia on c-cut sapphire. Having the ability to grow high-quality thin films of hafnium oxide allows studying the influence of defined oxygen deficiency on its physical properties, as the next step of this work. The optical properties changed dramatically from colourless and transparent for stoichiometric HfO2 to dark black and opaque for highly deficient films of HfO2-x. The optical band gap could be tuned within more than one eV, visualising the introduction of defects (oxygen vacancies) in situ during growth. In fact, Hafnia showed a metal to insulator transition as a function of the oxygen content, conductive HfO2-x exhibited electrical p-type conductivity with resistivities of 300 µWcm, charge carrier concentrations of 6 times 10 to the power of 21 cm-3 at mobilities of 2 cm²/(Vs). The observed conductivity seems to be intrinsic to oxygen deficient hafnia and not due to a percolation of a conducting phase in an insulating matrix, as evident from various characterisations. A simple defect band structure model has been developed based on the observations, covering the formation of defect bands within the band gap being responsible for electrical conductivity and absorption of radiation within the visible range. With respect to reports on high-Tc ferromagnetism, no evidence for d0-ferromagnetism and room temperature ferromagnetism in Ni-doped HfO2-x could be found.
| Typ des Eintrags: | Dissertation | ||||
|---|---|---|---|---|---|
| Erschienen: | 2012 | ||||
| Autor(en): | Hildebrandt, Erwin Matti | ||||
| Art des Eintrags: | Erstveröffentlichung | ||||
| Titel: | Oxygen Engineered Hafnium Oxide Thin Films grown by Reactive Molecular Beam Epitaxy | ||||
| Sprache: | Englisch | ||||
| Referenten: | Alff, Prof. Dr. Lambert ; Schröder, Prof. Dr. Thomas ; Donner, Prof. Dr. Wolfgang ; Ensinger, Prof. Dr. Wolfgang | ||||
| Publikationsjahr: | 14 Dezember 2012 | ||||
| Ort: | Darmstadt, Germany | ||||
| Datum der mündlichen Prüfung: | 28 Februar 2013 | ||||
| URL / URN: | http://tuprints.ulb.tu-darmstadt.de/3338 | ||||
| Zugehörige Links: | |||||
| Kurzbeschreibung (Abstract): | This study applies RMBE to grow thin films of hafnium oxide, a widely studied material which has found its way into commercialisation as a replacement of SiO2 in a field effect transistor. After investigating different substrates and probing various deposition conditions, RMBE-grown films of hafnium oxide yielded to epitaxial films of hafnia on c-cut sapphire. Having the ability to grow high-quality thin films of hafnium oxide allows studying the influence of defined oxygen deficiency on its physical properties, as the next step of this work. The optical properties changed dramatically from colourless and transparent for stoichiometric HfO2 to dark black and opaque for highly deficient films of HfO2-x. The optical band gap could be tuned within more than one eV, visualising the introduction of defects (oxygen vacancies) in situ during growth. In fact, Hafnia showed a metal to insulator transition as a function of the oxygen content, conductive HfO2-x exhibited electrical p-type conductivity with resistivities of 300 µWcm, charge carrier concentrations of 6 times 10 to the power of 21 cm-3 at mobilities of 2 cm²/(Vs). The observed conductivity seems to be intrinsic to oxygen deficient hafnia and not due to a percolation of a conducting phase in an insulating matrix, as evident from various characterisations. A simple defect band structure model has been developed based on the observations, covering the formation of defect bands within the band gap being responsible for electrical conductivity and absorption of radiation within the visible range. With respect to reports on high-Tc ferromagnetism, no evidence for d0-ferromagnetism and room temperature ferromagnetism in Ni-doped HfO2-x could be found. |
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| Alternatives oder übersetztes Abstract: |
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| Freie Schlagworte: | oxygen engineering, molecular beam epitaxy, hafnium oxide, HfO2, resistive switching, high-k dielectric, oxygen vacancies | ||||
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| URN: | urn:nbn:de:tuda-tuprints-33384 | ||||
| Sachgruppe der Dewey Dezimalklassifikatin (DDC): | 500 Naturwissenschaften und Mathematik > 500 Naturwissenschaften 600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften und Maschinenbau |
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| Fachbereich(e)/-gebiet(e): | 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft > Fachgebiet Dünne Schichten 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft 11 Fachbereich Material- und Geowissenschaften |
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| Hinterlegungsdatum: | 26 Mai 2013 19:55 | ||||
| Letzte Änderung: | 26 Mai 2013 19:55 | ||||
| PPN: | |||||
| Referenten: | Alff, Prof. Dr. Lambert ; Schröder, Prof. Dr. Thomas ; Donner, Prof. Dr. Wolfgang ; Ensinger, Prof. Dr. Wolfgang | ||||
| Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: | 28 Februar 2013 | ||||
| Schlagworte: |
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