Résumé
The step conguration of a vicinal Si surface is studied under electromigration and a gradient of temperature. An abrupt transition (∆T = 4C) from step-meandering to step-bunching is found at 1225 C for a step-down direct-current direction. This phase transition starts by local inhomogeneities which then extend on the whole surface. The transition is studied in the framework of a linear stability analysis of the usual Burton-Cabrera-Frank model by comparing the amplication factors of step-meandering and step-bunching instabilities. Both compete at a given temperature, but since the amplication factors behave dierently with temperature, bunching abruptly supersedes meandering above a critical temperature.