Semiconductor device having an active layer with separate layers where one of the layers acts as crystal nuclei for the other

摘要

A semiconductor device having a active layer comprising crystalline silicon, said active layer comprising a first layer comprising crystalline silicon formed on an insulating surface and a second layer comprising crystalline silicon formed on said first layer, wherein said first layer contains a metal element at a first concentration while said second layer is free from said metal element or contains said metal element at a second concentration which is lower than said first concentration.