Self-assembled Ge-islands for photovoltaic applications

We have fabricated silicon solar cells with embedded germanium layers to form three-dimensional islands in the Stranski–Krastanov growth mode. The additional Ge-layers increase the infrared absorption in the base of the cell to achieve higher overall photocurrent and overcome the loss in open circuit voltage of the heterostructure. In an UHV-MBE chamber up to 75 layers of germanium, each about 8 monolayers thick, separated by Si-spacer layers (9–View the MathML source were grown on each other using standard View the MathML source p-type Si-substrates. The density of islands in the layers was increased by the use of antimony as surfactant, thus densities View the MathML source were realized. The islands were covered by a View the MathML source thick Si-layer (n-type) on top which is used as emitter of the cell. Photoluminescence measurements, AFM and TEM-microscopy were used to characterize the growth of Ge-islands under various growth conditions and post-thermal treatment. Photocurrent measurements exhibit a higher response of the fabricated solar cells in the infrared regime compared to standard Si-cells.