Thin film transistor and method for manufacturing a thin film transistor

A method for manufacturing a thin film transistor, the method comprising:

• forming a first semiconductor layer, a gate dielectric layer, and a gate electrode sequentially on a substrate, wherein the first semiconductor layer has a first portion located in a channel region of the thin film transistor and a second portion located in a source/drain region of the thin film transistor and on both sides of the first portion, wherein the second portion and first sub-portions, adjacent to the second portion, of the first portion comprise an amorphous semiconductor material, and wherein a second sub-portion, between the first sub-portions, of the first portion comprises a polycrystalline semiconductor material;
• forming a second semiconductor layer in the source/drain regions and in contact with the second portion, wherein a conductivity of the second semiconductor layer is higher than a conductivity of the amorphous semiconductor material, wherein the second semiconductor layer is in contact with a surface of the second portion facing the substrate;
• and
• forming a source/drain electrode, wherein a surface facing away from the substrate of the second semiconductor layer is in contact with a surface facing towards the substrate of the second portion, and wherein a surface facing towards the substrate of the second semiconductor layer is in contact with a surface facing away from the substrate of the source/drain electrode.