Strain effects on polycrystalline germanium thin films
Toshifumi Imajo1,2, Takashi Suemasu3, Kaoru Toko4,5
1Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8573, Japan. toko@bk.tsukuba.ac.jp.
Scientific Reports
|April 16, 2021
Summary
Strain significantly impacts polycrystalline germanium (Ge) thin films. Tensile strain increases grain size and barrier height, while compressive strain decreases them, offering insights for Ge-based device design.
Area of Science:
- Materials Science
- Solid-State Physics
- Semiconductor Engineering
Background:
- Polycrystalline germanium (Ge) thin films offer high hole mobilities at low process temperatures, surpassing single-crystal silicon (Si).
- Understanding strain effects is crucial for optimizing Ge thin-film properties for advanced electronic applications.
Purpose of the Study:
- To investigate the influence of substrate-induced strain on the crystal and electrical properties of polycrystalline Ge thin films.
- To explore how tensile and compressive strains affect grain size, grain boundary potential barrier height, and overall film quality.
Main Methods:
- Formation of polycrystalline Ge thin films via solid-phase crystallization at 375°C on various substrates.
- Modulation of substrate materials to induce controlled tensile (approx. 0.5%) and compressive (approx. -0.5%) strain in Ge layers.
- Analysis of crystal properties, including grain size, and electrical properties, focusing on grain boundary potential barriers.
Main Results:
- Both tensile and compressive strains promote the growth of large crystal grains, reaching approximately 10 μm in size.
- The potential barrier height at grain boundaries is highly strain-dependent.
- Tensile strain increases the potential barrier height, whereas compressive strain decreases it.
Conclusions:
- Strain engineering is a key factor in controlling the microstructure and electrical characteristics of polycrystalline Ge thin films.
- The observed strain-dependent modulation of grain boundary potential barriers provides valuable insights for designing high-performance Ge-based thin-film devices.
- These findings are particularly relevant for the development of Internet-of-Things (IoT) technologies utilizing Ge thin films on diverse substrates.
