Prof. Erwin Peiner
TU Braunschweig, Germany
Semiconductor nanowire arrays for energy harvesting – fabrication and characterization
More than half of the worldwide produced energy is wasted and rejected to the environment. Semiconductor nanowire (NW) arrays are a subset of the class of nanomaterials, which can help to recover such waste energy from power generation, transportation, industrial processes, etc. They outperform the properties of their bulk counterparts by, e. g., a drastically lower thermal conductivity, which is beneficial for the figure of merit of thermoelectric heat recovery. Furthermore, many semiconductors are abundant, non-toxic, and environmentally benign and can be manufactured using highly developed nanofabrication methods. Nevertheless, as one of the key factors for future commercialization of NW-based energy harvesters, traceable high-throughput nanometrological tools are indispensable.
In an international project within the European Metrology Programme for Innovation and Research different top-down and bottom-up fabrication techniques of semiconductor NW arrays, e. g., cryogenic deep reactive ion etching (cryoDRIE), metal-assisted chemical etching (MACE), and chemical bath deposition/aqueous crystal growth (CBD/ACG) shall be compared and investigated with respect to their performance in piezoelectric harvesters, thermoelectric energy generators, and solar cells. Lithography available in the cleanroom laboratories of IHT and PTB, e.g., nano imprint lithography (NIL), nano sphere lithography (NSL), and e-beam lithography (EBL) will be described as used for fabricating various semiconductor NW structures under the control of many different structure parameters such as cross-sectional shape, diameter, length, orientation, surface roughness, doping concentration, elasticity, fracture limit and piezoelectric coefficients. For characterization and control of these parameters, various methods including conventional scanning probe microscopy (SPM) and MEMS-based SPM, Müller-matrix ellipsometry (MME), scatterometry, spreading resistance microscopy (SSRM), contact resonance force microscopy (CR-FM), nanoindentation and continuous stiffness measurement (CSM) technique are required. Their potential for high-throughput nanometrology and process control will be investigated, improved and demonstrated.