Abstract

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.

Highlights

  • The chemical effect of ultrasonic waves derives primarily from hot spots formed during acoustic cavitation in a chemical mixture

  • Two techniques related to ultrasonic cleaning of Si wafers and sonochemical modification of Si and SiGe surfaces in hydrocarbon solutions will be discussed

  • Two techniques related to ultrasonic cleaning of Si wafers and sonochemical modification of Si, SiGe and amorphous silicon (a-Si)/SiGe surfaces in hydrocarbon solutions of chloroform (CHCl3) and dichloromethane (CH2Cl2) are outlined

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Summary

Introduction

The chemical effect of ultrasonic waves derives primarily from hot spots formed during acoustic cavitation in a chemical mixture. Sonochemical techniques have been used in processing of semiconductor surfaces [5–14]. In this method, the main phenomenon is the acoustic cavitation, which enhances chemical reactions in a solution. The bubbles collapse, breaking the chemical bonds on the material surface. Two techniques related to ultrasonic cleaning of Si wafers and sonochemical modification of Si and SiGe surfaces in hydrocarbon solutions will be discussed. In both cases, the occurrence of cavitation and bubble implosion is necessary for ultrasonic cleaning and surface processing as it is known today. Exact mechanisms of an improved photoelectric behavior of Si-based micro- and nanostructures subjected to power ultrasound are not yet clarified in many cases, the likely scenarios behind the observed photovoltaic performances will be proposed to involve the surface chemistry of oxygen and hydrogen molecules as well hydrocarbon chains

Processing and passivation of Si wafers used for solar cells
Sonochemistry: basic principles
Ultrasonic cleaning of Si wafers
Sonochemical passivation of Si and SiGe
Conclusions
Findings
26. New York

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