Linear GeSn Grading in MBE for Defect and Strain Control

The patent implements dynamic adjustment of effusion cell temperatures during the growth process. The tin effusion cell temperature is continuously modified to achieve a linear increase in tin beam equivalent pressure, while the germanium effusion cell temperature is similarly adjusted. This dynamic control enables precise composition gradients without requiring complex post-growth processing, resolving the contradiction between film quality and process complexity.

The patent systematically changes multiple parameters including effusion cell temperatures, beam equivalent pressures, and growth rates. By coordinating changes in tin and germanium flux ratios throughout the growth process, the method achieves linear composition gradients and minimizes defects. This multi-parameter control strategy improves film quality while maintaining a manageable process through integrated control.

The patent performs preliminary grading of the GeSn composition before growing the final optoelectronic layers. By first creating a graded buffer layer with gradually increasing tin content, the lattice mismatch and strain are progressively managed. This preliminary action prepares the substrate to accommodate higher Sn compositions in subsequent layers, enabling direct bandgap material growth while minimizing strain-related defects.

The patent applies different composition gradients and growth conditions to different regions of the film structure. The buffer layer receives a gradual composition increase, while subsequent optoelectronic layers are grown with controlled Sn content. This local quality approach ensures each region has the appropriate composition for its function, maximizing optoelectronic performance while managing strain locally to prevent defects.