Mid-infrared (3-8 {\mu}m) $\text{Ge}_{1-y}\text{Sn}_y$ alloys (0.15 < $y$ < 0.30): synthesis, structural, and optical properties

TL;DR

This study reports the synthesis and analysis of GeSn alloys with 0.15< y<0.30 grown on silicon, revealing their structural and optical properties, including sharp mid-infrared absorption edges suitable for atmospheric applications.

Contribution

First demonstration of high-temperature growth of GeSn alloys on Si with detailed structural and optical characterization, highlighting their potential for mid-IR applications.

Findings

Alloys exhibit linear dependence of lattice parameter and Raman frequency on composition.

Sharp absorption edges up to 8 μm observed, with a cubic compositional dependence.

Potential for covering the 8-12 μm atmospheric window with these alloys.

Abstract

$\text{Ge}_{1-y}\text{Sn}_y$ alloys with compositions in the 0.15 < $y$ < 0.30 range have been grown directly on Si substrates using a chemical vapor deposition approach that allows for growth temperatures as high as 290 $^{\circ}$C. The films show structural properties that are consistent with results from earlier materials with much lower Sn concentrations. These include the lattice parameter and the Ge-Ge Raman frequency, which are found to depend linearly on composition. The simplicity of the structures, directly grown on Si, makes it possible to carry out detailed optical studies. Sharp absorption edges are found, reaching 8 $\mu$m near $y$ =0.3. The compositional dependence of edge energies shows a cubic deviation from the standard quadratic alloy expression. The cubic term may dramatically impact the ability of the alloys to cover the long-wavelength (8-12 $\mu$m) mid-IR atmospheric window.