May 10, 2012
Quantum dot photonic nanocrystals increase conversion efficiency of solar cells
Heteroepitaxy of a lattice-mismatched semiconductor system is known to result in the formation of quantum dots that exhibit unique physical properties. Further wet etching can form surface corrugations that couple to the buried quantum dots to realize photonic nanocrystals.
Scientists from the Institute for Materials Research, Tohoku University, Institute for Chemical Research, Kyoto University, and City University of Hong Kong, used a gas source molecular beam epitaxy system to grow vertically aligned Ge quantum dots.
By adopting a simple, but carefully controlled wet etch process, the team has shown that spatially modulated etch preferences can lead to realization of quantum dot photonic nanocrystals.
Furthermore, in their work the researchers proposed to integrate the structure in solar cells to exploit a number of advantages including efficient light trapping, increased absorption by quantum dots and suppression of carrier recombination by type-II band alignment at Ge/Si interface.
Reporting their results in the journal Nanotechnology, the scientists demonstrated the effectiveness of the proposed solar cell by observing a marked increase in the conversion efficiency of the device.
This simple approach provides a potentially useful tool to fabricate quantum dot photonic nanocrystals on various types of surface and devices in other photonic applications.
Additional information can be found in the journal Nanotechnology.
About the author
The work was in part supported by the Advanced Low Carbon Technology Research and Development Program (ALCA) of the Japan Science and Technology Agency (JST). Prof. Noritaka Usami is head of the project, designed experiments and carried out growth of vertically aligned quantum dots. Dr Wugen Pan is responsible for development of all the process including fabrication of solar cells. Prof. Takeshi Tayagaki performed the FDTD calculation. Prof. Sai Tak Chu contributed to the analysis and interpretation of the results.