The influence of film thickness and incident excimer laser energy density on the properties of poly-Si thin film transistors has been investigated and a coherent pattern of behavior has been identified which establishes controlled melt-through of the film as a key condition for achieving high quality devices. The conditions were correlated with the appearance of large grains and gave consistent results from bothn- andp-channel devices, with carrier mobilities of more than 150 and80 cm2/V s,respectively, and leakage currents of less than2×10−14 A/&mgr;m.From a study of static irradiations, using a semi-Gaussian laser beam, the results are shown to be consistent with the super lateral grain growth (SLG) model. The trailing edge of the beam, when used in a swept mode, has been demonstrated to play an important role in extending the size of the energy window for this effect by re-setting the material into the SLG regime. ©1997 American Institute of Physics.