A major problem of current silicon thin film solar cells lies in low carrier collection efficiency due to short carrier diffusion length. Instead of improving the collection efficiency in a relatively thick solar cell, increasing light absorption while still keeping the active layer thin is an alternative solution. Absorption enhancement in a thin film Si solar cell by incorporating a two-dimensional periodic metallic nanopattern was investigated using three-dimensional finite element analysis. By studying the enhancement effect brought by different materials, dimensions, coverage, and dielectric environments of the metal nanopattern, we found that absorption enhancement occurs at wavelength range outside surface plasmons resonance of the nanostructures. The exploitation of the nanostructures also enhances the Fabry-Perot resonance in the active layer. It plays an important role in optimizing the absorption of the solar cell.
We introduce a scheme incorporating wafer bonding and tunnel junctions to improve the performance long-wavelength Vertical Cavity Surface Emitting Lasers (VCSELs). Through careful design of PL-mode offset, mirror reflectivity, and aperture definition, we achieve lasing to 134°C, output power above 2 mW, single-mode output power at 80°C above 1 mW, and differential efficiencies of 46%. We achieve lasing at wavelengths as high as 1336 nm and show a versatile design that can be applied to any VCSEL functioning at long wavelengths.