Thin film transistor and display device

A thin film transistor comprising:

• a gate electrode layer;
• a first semiconductor layer;
• a second semiconductor layer having lower carrier mobility than the first semiconductor layer, which is provided on and in contact with the first semiconductor layer;
• a gate insulating layer which is provided between and in contact with the gate electrode layer and the first semiconductor layer;
• a pair of first impurity semiconductor layers which are provided on and in contact with the second semiconductor layer;
• a pair of second impurity semiconductor layers one of which is provided in contact with one of the first impurity semiconductor layers, side surfaces of the first semiconductor layer and the second semiconductor layer, and the other of which is provided in contact with the other of the first impurity semiconductor layers, side surfaces of the first semiconductor layer and the second semiconductor layer;
• a source electrode which is provided on and in contact with one of the second impurity semiconductor layers;
• and
• a drain electrode which is provided on and in contact with the other of the second impurity semiconductor layers,
• wherein an entire surface of the first semiconductor layer on the gate electrode layer side is shielded from light by the gate electrode layer.