Optical properties of reactive-ion-etched Si/Si_1-xGe_x heterostructures

A patterning technology for fabrication of nanometer structures in Si/SiGe heterosystems is developed. The method pursued here combines high-resolution electron-beam lithography with reactive-ion-etching pattern transfer. A modified SF₆/O₂ dry-etching process is optimized by varying the gas mixture to achieve the required anisotropy. Photoluminescence measurements are carried out on uniformly etched samples to determine the influence of the reactive-ion-etching process on the optical properties. Etch process induced surface modifications drastically alter the electrical surface potentials. They are identified by laser desorption. These modifications are partially removed by low-temperature postannealing steps. A qualitative model is presented to explain the observed effects. With this optimized technology, SiGe wires with lateral widths from 4 μm down to 25 nm are fabricated. Photoluminescence has been detected for structures as small as 600 nm.