Structural changes in flash lamp annealed amorphous Si layers probed by slow positron implantation spectroscopy

At the present time, great efforts are undertaken in order to improve the properties of photovoltaic elements. In case of Si-based solar cells the interest is focussed on a higher electrical efficiency connected with a more effective technology and with economies of scale. One of the possible methods for the realisation of this ambitious goal represents the Flash Lamp Annealing (FLA) technology. FLA allows a fast heating up of solid surfaces with a single light flash between some hundred microseconds and some milliseconds. Thereby, the achievable final temperature of the surface layer could be higher than the melting point depending on the intensity of the light flash. This method was applied to the modification of thin amorphous Si layers on SiO2 and glass. Slow Positron Implantation Spectroscopy (SPIS) was used for the characterisation of the microstructure before and after FLA. Changes in the structure down to a depth of some micrometers below the surface observed with SPIS will be presented and discussed.