Reflectance & surface morphology study of diamond wire cut silicon wafers for solar cells
Gautham Ravi Srinivas
Date of Issue2014
School of Mechanical and Aerospace Engineering
The silicon wafers for solar cells are generally sawn by two processes namely fixed abrasive diamond wire (FAW) and loose abrasive wire (LAW) sawn. The fixed abrasive diamond wire (FAW) sawing produces a smoother sawn wafer surface compared to the loose abrasive wire (LAW) sawn wafer. The literature study has shown that it is not possible to obtain the required surface morphology in diamond wire sawn wafers by using the existing wet etching protocol due to the presence of a potential mask which is the amorphous phase silicon . Therefore, it is important to etch away the amorphous silicon to achieve the required roughness and thereby reducing the reflectance. This project focuses on the removal of the amorphous phase silicon by anisotropic etching with potassium hydroxide (K.OH) followed by acidic etching with Buffered Oxide Etch (BOE) and isotropic etching contours. The acidic etching is done to bring the texture on the wafer surface. In all the experiments conducted etching time is considered as a key parameter . Micrograph analysis of the etched wafer shows that when the wafers are etched for a long period of time the texture diminishes. Hence it is important to have a time dependent etching of KOH to wash away the amorphous phase silicon and obtain the required texture. Raman spectra of the as-cut wafer before texturing consist of crystalline phase silicon and amorphous silicon (a potential mask) . In this project, the amorphous phase silicon is successfully removed and the surface morphology of the diamond wire sawn wafers is improved using KOH followed by acidic etching. It is elucidated and evident that etching for shorter time period gives favorable texture on the diamond wire sawn wafer so that light absorption is expected to increase.
DRNTU::Engineering::Aeronautical engineering::Materials of construction