Patent ID: 8921858

Claim:
A light-emitting device comprising a thin film transistor comprising: a gate electrode; a gate insulating film over the gate electrode; a microcrystalline semiconductor film over the gate insulating film, the microcrystalline semiconductor film including a channel formation region; a buffer layer over and in direct contact with the microcrystalline semiconductor film, the buffer layer comprising an amorphous semiconductor; source and drain regions over the buffer layer; source and drain electrodes over the source and drain regions; and an insulating film over the source and drain electrodes, and the source and drain regions, wherein entirety of one of the source and drain electrodes is over and in direct contact with one of the source and drain regions, wherein a part of an upper surface of the source and drain regions is in direct contact with the source and drain electrodes, wherein the other part of the upper surface of the source and drain regions is not in direct contact with the source and drain electrodes, wherein the other part of the upper surface of the source and drain regions and a part of the buffer layer are in direct contact with the insulating film, wherein at least a part of an upper surface of the one of the source and drain electrodes is in direct contact with the insulating film, wherein the buffer layer includes: a concave portion overlapping at least a part of the channel formation region; and an end portion, wherein the source and drain electrodes do not overlap with a horizontal upper surface of the end portion of the buffer layer, wherein a side of the concave portion is aligned with edge portions of the source and drain regions, and wherein the buffer layer contains nitrogen.