Semiconductor Nanostructures

The manufacture of semiconductor nanostructures via direct growth (bottom up) is an economically viable alternative to the manufacture via electron beam lithography (top down). For the former, our department possesses equipment for chemical vapor deposition (CVD) that makes the growth of silicon nanowires doped with boron and phosphorus possible. In addition, silicon nanostructures may also be created (e.g., on glass) through the wet chemical etching of silicon wafers or silicon layers.

The smallest gold droplets created, for example, through electron beam lithography are the starting point for nanowire growth during a vapor-liquid-solid process. The diameter of a wire grown using this method is mostly determined by the size of the metal droplet. If using a low-defect, clean, and monocrystalline substrate surface, the orientation of the nanowires can also be influenced. Under suitable manufacturing conditions these structures exhibit a strong photoluminescence.

The absorption of light is strongly determined by the diameter of the nanowires, which is of particular importance for the application of such wires in novel thin-film solar cells. The building blocks of these novel solar cells may be, for example, core/shell particles of differently doped crystalline silicon. After suitable nanomanipulation and contacting, the electrical properties of individual nanowires may be measured using electron beam lithography in a so-called “probe station.“

For diagnostic and structuring purposes we have a TESCAN dual-beam electron microscope (LYRAXMU series) at our disposal equipped with a focused Ga+ ion beam (FIB), electron beam scattered diffraction (EBSD), a detector for measuring electron beam-induced current (EBIC), and a nanomanipulator. In addition to nanowires, multicrystalline silicon solar cells and crystalline thin-film solar cells on glass may also be electrically and structurally analyzed with this device.

Further application examples can be found in sensor technology or the use of nanostructures as a substrate in surface-enhanced Raman scattering (SERS).