Hubmann, Andreas (2022)
Doped Indium Oxide: Surface Potentials, Electronic and Optical Properties.
Technische Universität Darmstadt
doi: 10.26083/tuprints-00017762
Dissertation, Erstveröffentlichung, Verlagsversion
Kurzbeschreibung (Abstract)
Objective of this work is to extend the experimental data base for doped In2O3 to provide a better understanding of this material and especially the effect of different dopant elements on the optical and electronic properties as well as surface potentials. Previous research on In2O3 is pursued by investigating Sn:In2O3, Ge:In2O3, Mo:In2O3 and Ti:In2O3 thin films. Thin films were grown by radio frequency magnetron sputtering. Multiple target compositions and deposition conditions, i.e. substrate temperature and oxygen content of the process atmosphere, were used. Transmission, reflection and spectroscopic ellipsometry measurements were carried out to distinguish optical properties. By simulation of those spectra optical carrier concentration and mobility could be compared to values obtained by conductivity and Hall-effect measurements. Photoelectron spectroscopy was used to access the surface electronic structure and its chemical composition. To correlate the crystal structure to former features, selected samples were analyzed by X-ray diffraction. Independent on the dopant element a decreasing carrier concentration is found with increasing oxygen chemical potential. This indicates interstitial oxygen to act as compensating defect. The conductivity tends to increase with temperature. Depending on the dopant and its concentration a complete loss of the carrier mobility may be found at high deposition temperatures. The carrier mobility and overall doping efficiency, going with the maximum carrier concentration, is highly dopant specific. The mobility is determined by the grain boundary barrier height, which is mainly influenced by dopant segregation. Several effects, possibly limiting the carrier concentration are discussed. Dopant segregation at the surface is found for almost all investigated materials. Depending on the element either oxidizing or reducing conditions lead to enhanced segregation. While Ti behaves similar to Sn, increasing Ge and Mo surface concentrations are measured for oxidizing conditions. No correlation to the Fermi level position is found in those two cases. Possible reasons for the contrasting conditions based on defect chemistry, oxide stability and ionic radii are discussed. Surface potentials were found to be subject to the doping elements. The wide variety in surface dipole is expected to be due to the formation of dopant oxide layers. A correlation to the surface termination and orientation as seen for In2O3 cannot be confirmed for any dopant element.
Typ des Eintrags: | Dissertation | ||||
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Erschienen: | 2022 | ||||
Autor(en): | Hubmann, Andreas | ||||
Art des Eintrags: | Erstveröffentlichung | ||||
Titel: | Doped Indium Oxide: Surface Potentials, Electronic and Optical Properties | ||||
Sprache: | Englisch | ||||
Referenten: | Klein, Prof. Dr. Andreas ; Albe, Prof. Dr. Karsten | ||||
Publikationsjahr: | 2022 | ||||
Ort: | Darmstadt | ||||
Kollation: | 167 Seiten | ||||
Datum der mündlichen Prüfung: | 15 Juni 2021 | ||||
DOI: | 10.26083/tuprints-00017762 | ||||
URL / URN: | https://tuprints.ulb.tu-darmstadt.de/17762 | ||||
Kurzbeschreibung (Abstract): | Objective of this work is to extend the experimental data base for doped In2O3 to provide a better understanding of this material and especially the effect of different dopant elements on the optical and electronic properties as well as surface potentials. Previous research on In2O3 is pursued by investigating Sn:In2O3, Ge:In2O3, Mo:In2O3 and Ti:In2O3 thin films. Thin films were grown by radio frequency magnetron sputtering. Multiple target compositions and deposition conditions, i.e. substrate temperature and oxygen content of the process atmosphere, were used. Transmission, reflection and spectroscopic ellipsometry measurements were carried out to distinguish optical properties. By simulation of those spectra optical carrier concentration and mobility could be compared to values obtained by conductivity and Hall-effect measurements. Photoelectron spectroscopy was used to access the surface electronic structure and its chemical composition. To correlate the crystal structure to former features, selected samples were analyzed by X-ray diffraction. Independent on the dopant element a decreasing carrier concentration is found with increasing oxygen chemical potential. This indicates interstitial oxygen to act as compensating defect. The conductivity tends to increase with temperature. Depending on the dopant and its concentration a complete loss of the carrier mobility may be found at high deposition temperatures. The carrier mobility and overall doping efficiency, going with the maximum carrier concentration, is highly dopant specific. The mobility is determined by the grain boundary barrier height, which is mainly influenced by dopant segregation. Several effects, possibly limiting the carrier concentration are discussed. Dopant segregation at the surface is found for almost all investigated materials. Depending on the element either oxidizing or reducing conditions lead to enhanced segregation. While Ti behaves similar to Sn, increasing Ge and Mo surface concentrations are measured for oxidizing conditions. No correlation to the Fermi level position is found in those two cases. Possible reasons for the contrasting conditions based on defect chemistry, oxide stability and ionic radii are discussed. Surface potentials were found to be subject to the doping elements. The wide variety in surface dipole is expected to be due to the formation of dopant oxide layers. A correlation to the surface termination and orientation as seen for In2O3 cannot be confirmed for any dopant element. |
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Alternatives oder übersetztes Abstract: |
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Status: | Verlagsversion | ||||
URN: | urn:nbn:de:tuda-tuprints-177628 | ||||
Sachgruppe der Dewey Dezimalklassifikatin (DDC): | 500 Naturwissenschaften und Mathematik > 500 Naturwissenschaften 500 Naturwissenschaften und Mathematik > 530 Physik |
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Fachbereich(e)/-gebiet(e): | 11 Fachbereich Material- und Geowissenschaften 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft > Fachgebiet Elektronenstruktur von Materialien |
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Hinterlegungsdatum: | 24 Jun 2022 12:07 | ||||
Letzte Änderung: | 27 Jun 2022 05:42 | ||||
PPN: | |||||
Referenten: | Klein, Prof. Dr. Andreas ; Albe, Prof. Dr. Karsten | ||||
Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: | 15 Juni 2021 | ||||
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