Growth and Characterization of SiGeSn Heterostructures for Photovoltaic and Optoelectronic Applications

Background/Relevance 

• Current solar photovoltaic systems have seen significant improvements in recent years but most still grapple with drawbacks ranging from excessive cost to lagged performance.
• A new group IV alloy SiGeSn thin film is proposed to address these issues through the growth of high quality, lattice-matched, tunable band gap, and CMOS compatible material for improved solar efficiency.

Innovation

• Explore innovative growth techniques to reduce defects for material integration of GeSn and other group IV alloys on Si.

Approach

• Growth of group IV alloys in a hot wire plasma enhanced cold walled UHV-CVD using precursor gases.
• Investigate Sn droplet formation on grown alloy films.
• Characterize materials using PL, Ellipsometry, Raman Spec., XRD, TEM and other material characterization tools.
• Optimize growth recipes to produce substrate quality GeSn virtual substrate.
• Growth of solar multi-junction heterostructures.

Key Results

• One/two-step Ge-buffer films and plasma-enhanced growth has been demonstrated at low temperatures.
• Sn phase segregation were observed on select samples at certain growth conditions.
• Investigated specific growth conditions sponsoring Sn phase segregation effects.
• Sn droplets population were seen to reduce following an etching procedure.

Conclusion

• Findings from previous growth efforts reveals the impact of optimized growth temperatures and Sn overpressure on material quality [Grant et al, 2018].
• On-going Sn-droplets segregation analysis could provide details on extent of impending limitations posed to underlying growth layers.

Future Work

• Characterize and compare before and after etching outcomes.
• Optimize growth conditions for enhanced material quality on:
•                                        GeSn on Ge buffered Si.
•                                        Plasma enhanced GeSn on Ge buffered Si