Abstract
In the past studies have shown that the addition of Ge and Sn into Si lattice to form SiGeSn enhances its carrier mobility and band-gap properties. Conventionally SiGeSn epitaxial films are grown using Ultra-High Vacuum (UHV) conditions with pressures ranging from 10-8 torr to 10-10 torr which makes high volume manufacturing very expensive. On the contrary, the use of low-pressure CVD processes (vacuum levels of 10-2 torr to 10-4 torr) is economically more viable and yields faster deposition of SiGeSn films. This study outlines the use of a cost-effective Plasma Enhanced Chemical Vapor Deposition (PECVD) reactor to study the impact of substrate temperature and substrate type on the growth and properties of polycrystalline SiGeSn films. The onset of polycrystallinity in the films is attributed to the oxygen-rich PECVD chamber conditions explained using the Volmer-Weber (3D island) mechanism. The properties of the films were characterized using varied techniques to understand the impact of the substrate on film composition, thickness, crystallinity, and strain.
Highlights
This study outlines the use of a cost-effective Plasma Enhanced Chemical Vapor Deposition (PECVD) reactor to study the impact of substrate temperature and substrate type on the growth and properties of polycrystalline SiGeSn films
The reactor consisted of a cylindrical quartz chamber with two injection lines at the top for the precursors, a gas delivery system and a vacuum exhaust system connected through flange at the bottom
It was observed that the temperatures between 350 ̊C and 380 ̊C resulted in films with structurally uniform lattices with roughnesses seen in the Nanoscale
Summary
Polycrystalline GeSn and SiGeSn alloys are not employed for photonic applications, their enhanced carrier mobility compared to polycrystalline Si make them attractive candidates in transistors and tandem solar cells [7] They find applications in thermoelectric generators due to their low thermal conductivities [8]. The researchers at the Arizona State University developed a hot wall ultra-high vacuum CVD system to deposit films using higher-order silanes and germanes along with stannane (SnD4) as the precursors for Si, Ge and Sn [19] [20] [21]. In order to grow on Si (001) directly and on the Ge-buffer layer, a novel precursor combination SnD4/Ge2H6/Si3H8 had to be introduced and at low growth temperatures, SiGeH6 was added to fine-tune the Si concentration [22]. The focal point of this manuscript is the effect of the substrate type on the SiGeSn film properties
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