1. Formation of heavily boron-doped hydrogenated polycrystalline germanium thin films by co-sputtering for developing p+ emitters of bottom cells
- Author
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Tsao, Chao-Yang, Huang, Jialiang, Hao, Xiaojing, Campbell, Patrick, and Green, Martin A.
- Subjects
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POLYCRYSTALLINE semiconductors , *GERMANIUM compounds , *THIN films , *BORON , *SEMICONDUCTOR doping , *HYDROGENATION , *SOLAR cells , *RAPID thermal processing , *X-ray diffraction , *SPUTTERING (Physics) - Abstract
Abstract: Properties of heavily boron-doped hydrogenated polycrystalline germanium (Ge) films sputter-deposited on glass are investigated for developing p+ emitters of the bottom cells of low cost monolithic tandem solar cells. The films were deposited and in-situ doped by co-sputtering Ge with boron at various power levels (P B) in a mixture of argon and hydrogen at 500°C, and then followed by a rapid thermal anneal process at 550°C for 120s or 600°C for 60s, respectively. The dependence of the structural properties of the films on the various boron incorporations as well as annealing conditions was explored by Raman and X-ray diffraction measurements. We find that the films as deposited at 500°C are polycrystalline with strong (220) preferential orientation, which are normally of columnar structure, confirmed by cross-sectional transmission electron microscopy. Revealed by Hall measurements, a boron activation level of 6.24×1019 atoms/cm3, well above reported maximum solid solubility in crystalline Ge, was obtained in the as deposited film at P B=55W. Annealing at 600°C enhanced the concentration to 1.21×1020 atoms/cm3. A fact that boron hardly diffuses in Ge at temperatures below 800°C makes the resultant material an excellent candidate for thin p+ emitters of the bottom cells of monolithic tandem solar cells. [ABSTRACT FROM AUTHOR]
- Published
- 2011
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