Graded Buffer Bragg Reflectors with High Reflectivity and Transparency for Metamorphic Optoelectronics

Ryan France, Jeronimo Buencuerpo, Mikayla Bradsby, John Geisz, Yukun Sun, Pankul Dhingra, Minjoo Lee, Myles Steiner

Research output: Contribution to journalArticlepeer-review

8 Scopus Citations


A graded buffer Bragg reflector (GBBR) is a bifunctional device component that provides the reflection of a distributed Bragg reflector and the adjustable lattice constant of a compositionally graded buffer. Prior work showed that these properties can be combined with low threading dislocation density and high reflectivity. Here, we design and demonstrate complex GBBRs for specific metamorphic solar cell applications. We design buffers that provide (1) high reflectivity over a narrow bandwidth, for quantum well solar cells, (2) reflectivity over a wide bandwidth, for optically thin solar cells, and (3) low sidelobe reflection, for multijunction devices that demand low out-of-band reflection. Apodized and triple GBBRs are demonstrated, and transparency is always considered, requiring designs with carefully engineered material combinations. A GBBR with a reflection of 99% is demonstrated, as well as a triple GBBR that has over 80% reflection for 100 nm of the spectrum around 800 nm. We also analyze potential deviations in a baseline GBBR from that of a perfect DBR using transmission electron microscopy to analyze imperfections in the material and modeling to analyze the impact of imperfect refractive index data for lattice-mismatched AlGaInAs. Minimal crosshatch roughness and unintentional thickness variation occur throughout the buffer, which likely influences reflection slightly. Small deviations between the calculated AlGaInAs and utilized AlGaAs refractive index exist, giving methods for future GBBR improvement. While the GBBR designs are intended for metamorphic solar cells, the broad and high reflection may also be useful for other optoelectronic devices such as light-emitting diodes or lasers.

Original languageAmerican English
Article number173102
Number of pages12
JournalJournal of Applied Physics
Issue number17
StatePublished - 7 May 2021

Bibliographical note

Publisher Copyright:
© 2021 Author(s).

NREL Publication Number

  • NREL/JA-5900-79186


  • Bragg reflector
  • graded buffer
  • III-V
  • metamorphic
  • multijunction solar cells


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