Abstract
This work studies the spontaneous self-assembly of Ge QDs on AlAs, GaAs and AlGaAs by high-temperature in␣situ annealing using molecular beam epitaxy (MBE). The morphology of Ge dots formed on AlAs were observed by atom probe tomography, which revealed nearly spherical QDs with diameters approaching 10 nm and confirmed the complete absence of a wetting layer. Reflection high-energy electron diffraction and atomic force microscopy of Ge annealed under similar conditions on GaAs and Al0.3Ga0.7As surfaces revealed the gradual suppression of QD formation with decreasing Al-content of the buffer. To investigate the prospects of using encapsulated Ge dots for upconverting photovoltaics, in which photocurrent can still be generated from photons with energy less than the host bandgap, Ge QDs were embedded into the active region of III–V PIN diodes by MBE. It was observed that orders of magnitude higher short-circuit current is obtained at photon energies below the GaAs bandgap compared with a reference PIN diode without Ge QDs. These results demonstrate the promise of Ge QDs for upconverting solar cells and the realization of device-quality integration of group IV and III–V semiconductors.
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Acknowledgements
This work was supported by the National Science Foundation under CBET-1438608, and by the Notre Dame Integrated Imaging Facility and MIND center. The authors declare no financial conflicts of interest. The authors also thank Alexander Mintairov for technical assistance.
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O’Brien, W.A., Qi, M., Yan, L. et al. Self-assembled Ge QDs Formed by High-Temperature Annealing on Al(Ga)As (001). J. Electron. Mater. 44, 1338–1343 (2015). https://doi.org/10.1007/s11664-014-3583-6
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DOI: https://doi.org/10.1007/s11664-014-3583-6