Ultrasonic Processing of Si and SiGe for Photovoltaic Applications

The usage of power ultrasound for sonochemical processing of Si wafers and thin layers of amorphous Si and SiGe alloys is described. Over the last decade different industries have become increasingly drawn to sonochemistry because it provides a green and clean alternative to conventional technologies, particular in the areas of processing of silicon-based materials for photovoltaic applications. Two techniques related to ultrasonic cleaning of Si wafers and sonochemical modification of Si, SiGe and a-Si/SiGe surfaces in hydrocarbon solutions of chloroform (CHCl3) and dichloromethane (CH2Cl2) are discussed. The occurrence of cavitation and bubble implosion is an indispensable prerequisite for ultrasonic cleaning and surface processing as it is known today. The use of higher ultrasonic frequencies to expand the range of ultrasonic cleaning and processing capabilities is emphasized. Although exact mechanisms of an improved photoelectric behavior of Si-based structures subjected to power ultrasound are not yet clarified in many cases, the likely scenarios behind the observed photovoltaic performances of Si, SiGe and a-Si/SiGe surfaces are proposed to involve the surface chemistry of oxygen and hydrogen molecules as well hydrocarbon chains.