Enhanced quantum efficiency of solar cells with self-assembled Ge dots stacked in multilayer structure

We report on the performance of solar cells with stacked self-assembled Ge dots in the intrinsic region of Si-based p-i-n diode. These dots were epitaxially grown on p-type Si(100) substrate via the Stranski-Krastanov growth mode by gas-source molecular beam epitaxy. Enhanced external quantum efficiency (EQE) in the infrared region up to 1.45 mum was observed for the solar cells with stacked self-assembled Ge dots compared with that without Ge dots. Furthermore, the EQE was found to increase with increasing number of stacking. These results show that electron-hole pairs generated in Ge dots can be efficiently separated by the internal electric field, and can contribute to the photocurrent without considerable recombination in Ge dots or at Ge/Si interfaces. (C) 2003 American Institute of Physics.