Laser speckle studies of silicon wafer for solar cell devices

Abstract

Silicon occupies a dominant space in photovoltaic industry for the manufacturing of solar cells. Performance of the photovoltaic panels depend upon the quality of the silicon wafer substrate. Identifying the good optically rough, defect free and mechanically stable wafers are paramount important for an efficiency improvement. The property and functionality of the wafer mainly depend upon the surface roughness. Roughness can be assessed while the light interacts with the surface. An intimate connection between surface roughness and reflectance is a well-known one for researchers. In order to reduce the reflectance, it is an essential to identify the silicon wafer with good optical roughness. Hence, in this present investigation non-contact, less expensive and real time Laser speckle Imaging set up is used as a characterisation tool to get data about the surface roughness by means of Fractal Dimension of silicon wafer. The Fractal Dimension (FD) describe the surface roughness of optically rough silicon wafer from the laser speckle images. newlineA commercially available silicon wafer Grade-A with thickness of 180and#956;m, breadth 2 cm and length 7 cm has been selected as a specimen. The specimen without any crack and contamination is picked for an investigation. The laser speckle imaging set up consists of laser source, silicon wafer and CCD camera with personal computer for image processing. An optically rough silicon wafer is irradiated by a highly coherent semiconductor diode laser of wavelength 532nm with 5mw power. The speckle images are constructed due to self-interference effect caused by the scattered light from the specimen. The speckle formation is caught by a good resolution CCD camera. The sample is rotated at different angles like 2º, 4º and 6º. Images are recorded and further processed for surface roughness evaluation by using Image J software. newline