Eintrag weiter verarbeiten
Structural, optical and switching properties of epitaxial Ge-Sb-Te thin films
Gespeichert in:
| Personen und Körperschaften: | |
|---|---|
| Titel: | Structural, optical and switching properties of epitaxial Ge-Sb-Te thin films |
| Hochschulschriftenvermerk: | Dissertation, Universität Leipzig, 2019 |
| Format: | E-Book Hochschulschrift |
| Sprache: | Englisch |
| veröffentlicht: |
Online-Ausg..
2020
|
| Schlagwörter: | |
| Quelle: | Qucosa |
| Zusammenfassung: | This thesis is devoted to the fabrication, optical characterization and switching behaviour of the prototypical chalcogenide-based phase-change material Ge2Sb2Te5, which is employed in non-volatile optical and electrical data storage devices. While common studies on conventional memory applications of Ge2Sb2Te5 are based on reversible amorphous to polycrystalline phase transitions, this thesis particularly focuses on the use of Ge2Sb2Te5 thin films of epitaxial, single-crystalline like nature aiming to gain deeper insights into structure-property correlations and novel switching pathways. The first part of this thesis deals with the growth of epitaxial Ge2Sb2Te5 thin films on Si(111) substrates by pulsed laser deposition with strong emphasis on controlling the degree of structural order in the thin films resulting from the distribution of intrinsic vacancies in the crystalline state of the material. As a result, highly vacancy-ordered epitaxial Ge2Sb2Te5 thin films in the thermodynamically stable as well as in the metastable crystalline phase are obtained, possessing a pronounced nanostructuring due to periodically spaced Van-der-Waals gaps or vacancy layers. Besides that, epitaxial Ge2Sb2Te5 thin films with complete disordered vacancy distributions are realized. Based on the achieved single-phase quality of the epitaxial thin films, a classification of the optical property contrast of different crystalline Ge2Sb2Te5 phases with respect to their vacancy ordering is presented. Beyond that, the impact of vicinal substrate surfaces on the phase, structure as well as on surface pattern formation in epitaxial Ge2Sb2Te5 thin films is investigated. The second part of this thesis employs epitaxial Ge2Sb2Te5 thin films as a model system to follow ns-laser induced structural modifications ranging from reversible crystalline to amorphous phase transitions to interface assisted epitaxial recrystallization processes. In particular, by applying single ns-laser pulses to the thin films, the transition from the vacancy ordered stable to the vacancy disordered metastable crystalline structure of Ge2Sb2Te5 via a transient molten phase is realized while the epitaxial nature of the thin films is preserved. This transition mechanism provides access to ultrafast crystal growth dynamics in an epitaxial phase-change material thin film model system offering the advantage of high crystalline quality and application-relevant sizing. By introducing a method that combines time-resolved reflectivity measurements with high resolution scanning transmission electron microscopy, crystal growth velocities upon fast cooling after single ns-laser pulse irradiation are determined. As a result, an increase in crystal growth velocity from 0.4 to 1.7 m/s with increasing laser fluence is observed with the maximum rate of 1.7 m/s as the upper detectable limit of the studied material. |
|---|