3D Patterning of Semiconductors for Energy Harvesting Devices

Our group is interested in novel semiconductor devices for energy harvesting, e g. solar cell, thermoelectrics, and batteries. One of our approaches for fabrication is top-down etching using metal assisted chemical etching (MacEtch) of semiconductors (mainly silicon). It uses noble metal (such as Au, Pt and Ag) deposited on the surface of a semiconductor (e.g. Si) as a catalyst to catalyze the hole (h+) generation from an oxidant (such as H2O2) in an acidic solution (such as HF) to induce local oxidation (Si + 4h+ &rarr Si4+) and reduction (2H+ + 2e- &rarr H2&uarr) reactions. This results in the removal of semiconductor materials without net consumption of the metal. The reactions occur only at the interface between metal and the semiconductor, under controlled etching conditions. As a result, metal descends into the semiconductor as the semiconductor is being etched right underneath, acting as a negative resist etch mask. When the catalyst metal is patterned in any shape and dimension, the pattern can be engraved into the semiconductor to produce micro and nanostructures including arrays of pillars for energy applications. MacEtch is essentially a wet etching method yet produces anisotropic high aspect ratio semiconductor micro and nanostructures without incurring lattice damage. MacEtch produced semiconductor nanostructures can be integrated into solar cells with better absorption and collection efficiency, for thermoelectric devices with low thermal conductivity when the sidewalls are rough, and for batteries with greater energy density.

Formation of an array of silicon pillars using mesh-patterned Ag-MacEtch.