Strain Relaxation and Relative Defect Density with Thickness in MBE-Grown Ge0.85Sn0.15 on Ge(001)
Dinesh Baral1,2, Nirosh M Eldose1, Diandian Zhang1
1Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, Arkansas 72701, United States.
Crystal Growth & Design
|July 6, 2026
Summary
Controlling germanium-tin (GeSn) alloy film thickness is key to reducing defects and enabling strain relaxation. This research defines an optimal thickness window for high-quality, silicon-compatible mid-infrared optoelectronics.
Area of Science:
- Materials Science
- Semiconductor Physics
- Optoelectronics
Background:
- Germanium-tin (GeSn) alloys offer tunable direct bandgaps for silicon-compatible optoelectronics.
- High Sn content in GeSn films is challenging due to strain-induced defects.
Purpose of the Study:
- Investigate the impact of film thickness on strain relaxation, defect density, and Sn segregation in GeSn alloys.
- Determine an optimal growth window for high-quality GeSn films.
Main Methods:
- Grew GeSn films with varying thicknesses (∼15% Sn).
- Analyzed strain relaxation using X-ray diffraction reciprocal space mapping (XRD-RSM).
- Evaluated defect density via photoluminescence measurements.
Main Results:
- Increased GeSn thickness promotes strain relaxation and reduces defect-related emission.
- Sn segregation begins around 150 nm thickness, identified by XRD-RSM.
- An effective growth window of 35–150 nm was established for relaxed, defect-suppressed GeSn.
Conclusions:
- Film thickness is critical for balancing strain relaxation and defect suppression in GeSn alloys.
- Optimized thickness control advances fabrication of high-quality, high Sn-content relaxed GeSn.
- Findings support the use of molecular beam epitaxy for advanced GeSn device fabrication.
