Photovoltaic Performance of Si and SiGe Surfaces Sonochemically Activated in Dichloromethane

Aims: To activate Si and SiGe surfaces by employing the sonochemical treatment at different operating frequencies in dichloromethane to improve the surface photovoltage signal. Background: To produce integrated electronic devices, one needs to achieve low surface and interface trap densities. In this respect, placing a passivating thin layer on Si and Ge surfaces, which saturates the electronic levels of traps and therefore affects the carrier recombination velocities at the surface, is of great interest. Objective: Demonstrating the effectiveness of the treatment of Si and SiGe surfaces depends on the ultrasonic frequency used. Methods: Photovoltaic transients, electron microscopy, EDX spectroscopy. Results: The surface photovoltage (SPV) decay curves can be divided into rapid (Τ1) and slow (Τ2) components. The sonication effect on the SPV is different for the treatment done at about 25 and 400 kHz. The SPV signal in Si gradually increases with increasing lower-frequency sonication time, whereas the SPV enhancement on SiGe is somewhat smaller. Increasing the sonication time increases the amplitude of the Τ2 component in Si. In SiGe, the lower-frequency sonication quenches the Τ2 component yielding a nearly single-exponential decay form. This trend is even more pronounced at the higher-frequency sonication. Conclusion: The sonochemical treatments greatly intensify the formation of CxHy–Si, and CxHy– Ge bonds on Si and Si1-xGex surfaces, resulting in increased SPV signals and prolonged SPV decay times. These results demonstrate that sonochemical treatment is a more effective technique to obtain stable highly passivated Si and Si1-xGex surfaces in comparison with wet chemical treatments in hydrocarbon solutions.