Study on growth of epitaxial single domain tin-telluride and epitaxial antimony on silicon and sputter-grown bismuth-tin-telluride nanowhiskers

• Wachstumsuntersuchung von epitaktischem Zinntellurid und epitaktischem Antimon auf Silizium und gesputterten Bismut-Zinn-Tellurid Nanowhiskern

Wirtssohn, Matti; Wuttig, Matthias (Thesis advisor); Waser, Rainer (Thesis advisor)

Aachen (2019, 2020)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2019

Abstract

This work mainly deals with the deposition and characterization of thin films on silicon surfaces. Within this work, three different material systems are studied. Consequently it is divided into the following three sections:1. Epitaxial growth of SnTe(001) on Si(111)2. Epitaxial growth of Sb(0001) on Si(111)3. Sputter-grown bismuth-tin-telluride nanowhiskers. The first two segments focus on investigation and discussion of the growth process and resulting structure of the given materials. The third chapter however, is centered more on the handling and preparation of sputtered crystalline nanostructures to test their feasibility for further device fabrication. The growth process of epitaxial SnTe(001) on Si(111)−$\sqrt3$×$\sqrt3$−R30°−Sb terminated surfaces is studied. From the combination of the threefold symmetry of the Si(111) surface and the fourfold symmetry of the cubic SnTe(001) layer, a twelve-fold symmetry of three energetically equivalent rotational domains should expectably emerge. The presented films however, are single-domain SnTe(001) films. It will be shown, that by alignment of the wafer miscut and the Sb surface termination, the rotational symmetry of the film-substrate interface can be eliminated. As a result the SnTe(001) layers are governed by only one rotational domain. These findings are compared to SnTe(001) films grown on Si(111) − 7 × 7 reconstructed surfaces, consisting of six rotational domains. This illustrates the vast improvements made possible by the presented growth process. This mechanism of breaking the symmetry condition at the film-substrate interface might likewise apply similarly to other systems. Furthermore the gathered information on SnTe growth behavior is exploited to fabricate single-domain SnTe(001) devices for electrical testing. Electrical testing is carried out at temperatures between 2 K and 300 K. The devices consist of SnTe layers with a Sn contents of 50.0 at.% to 51.5 at.%. The growth of epitaxial Sb on the Si(111) − 7 × 7 surface reconstruction is presented. Highly out-of-plane textured Sb(0001) layers were produced by molecular beam epitaxy. Substrate temperature, deposition rate and film thickness are varied and compared. In all scenarios the film consists of predominantly smooth and flat Sb(0001) and some Sb(01$\bar1$2) grains. The observations suggests that at first the step edges and Si(111) − 7 × 7 domain boundaries on the surface are decorated with approximately 2 nm Sb. Then the film starts growing from these decorated steps as crystalline Sb(0001) islands. The Sb(01$\bar1$2) grains are found to emerge on these steps/domain boundaries as well. The Sb(0001) films exhibit rotational domains of ±6.1°, ±16.0° and ±30.1° regarding the silicon substrate. The results are compared to GeTe and Sb$_{2}$Te$_{3}$ films grown under comparable conditions. Sputter-grown Sn$_{x}$Bi$_{y}$Te$_{z}$ nanowhiskers are presented. Structural analysis determines highly ordered nanowhiskers free of structural defects. Analysis of the composition yields a Sn$_{1}$Bi$_{2}$Te$_{4}$ stoichiometry. The presented handling of the nanostructures shows that further processing can be done to fabricate functional devices. Conducted 4-terminal-sensing is performed as a proof of concept, showing that other methods of characterization are possible on the devices.

Institutions

• Department of Physics [130000]
• Chair of Experimental Physics I A and I. Institute of Physics [131110]