Growth studies of Ge-islands for enhanced performance of thin film solar cells

Abstract We have studied the self-organized growth of Ge-islands on Si-substrates in the Stranski–Krastanow growth mode with Si MBE for the use in thin film solar cells. For samples with high Ge concentrations and high crystal quality the increased infrared absorption of the SiGe-islands incorporated in the base material of a Si solar cell should overcome the reduced open circuit voltage due to the lower band gap for high Ge-concentrations ( x >0.8). Series with different Ge-coverage and growth temperatures from 500°C to 700°C have been grown to optimize Ge-island formation and crystal quality of single and multiple island layers. Photoluminescence measurements, atomic force and transmission electron microscopy exhibit three-dimensional growth at temperatures around 650°C and 8 monolayers of Ge-coverage and highly ordered Ge-islands with lateral densities up to 1×10 11 cm −2 have been realized. In addition, the use of Sb as surfactant during Ge-island growth was studied intensively and solar cells have been fabricated from this material.