PREPARATION OF THICK POLYCRYSTALLINE SILICON LAYERS ON GLASS BY LASERIRRADIATION

For polycrystalline silicon thin film solar cells a silicon layer 50 m u m thick is required consisting of grains 100 mu m in diameter deposi ted on low cost glass substrate. We report on a preparation method com bining plasma enhanced CVD of amorphous silicon and laser crystallizat ion. We start from a-Si:H thin films 200 nm thick which are deposited on glass (Corning 7059) by a rf-CVD process. These films are irradiate d by scanning with an Ar+ laser to result in crystals of several 10 mu m in diameter. In order to increase the film thickness on this crysta lline seed layer further amorphous silicon is deposited by the same CV D process at a rate of 20 nm/min. During the deposition the growing la yer is irradiated by excimer laser pulses with about 300 mJ/cm(2) at a repetition rate of less than 0.1 Hz. Each laser pulse melts the newly deposited amorphous layer down to the crystalline interface which act s as a homoepitactic substrate during resolidification. In this way th e whole growing amorphous layer is converted to a polycrystal. (C) 199 8 Elsevier Science S.A.