Low Temperature Growth of Group IV Materials for Optoelectronics Applications

Student: Oluwatobi G. Olorunsola

Degree: Ph.D., December 2021

Major Professor: Dr. Fisher Yu

Research Area(s):

Microelectronics

Photonics

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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.

Conclusions

  • 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