R Ginige et al 2006 Semicond. Sci. Technol. 21 775 doi:10.1088/0268-1242/21/6/011
R Ginige1, B Corbett1, M Modreanu1, C Barrett1, J Hilgarth2, G Isella3, D Chrastina3 and H von Känel3
Show affiliationsA virtual substrate consisting of a Ge layer grown directly on Si without an intervening SiGe graded layer is characterized. The nominally 100% Ge overlayer is fully relaxed and contains a small amount (3%) of unintentional Si. A dislocation density of 108 cm−2 is estimated for the virtual substrate prior to GaAs epitaxial growth, which is reduced by a factor of 100 after the growth of GaAs. On this novel virtual substrate 1 cm2 single-junction GaAs photovoltaic cells were realized with an efficiency of 11.7% under AM0 compared with 20.2% for cells grown on a crystalline Ge substrate. Due to the high dislocation density a 50-fold higher dark current is measured in the virtual substrate cells compared to the crystalline Ge cells, leading to a lower short circuit current and open-circuit voltage of the cells fabricated on the virtual substrates. The post-GaAs growth dislocation density is estimated as 1 × 107 cm−2 in the base region and 4 × 105 cm−2 in the emitter region based on modelling and measurements.
68.47.Fg Semiconductor surfaces
68.35.Dv Composition, segregation; defects and impurities
68.55.A- Nucleation and growth
84.60.Jt Photoelectric conversion: solar cells and arrays
Issue 6 (June 2006)
Received 13 January 2006, in final form 7 March 2006
Published 19 April 2006
R Ginige et al 2006 Semicond. Sci. Technol. 21 775
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