Reverse conducting-insulated gate bipolar transistor

A reverse conducting-insulated gate bipolar transistor, comprising:

• a second base layer of a second conductive type provided on a second principal surface opposite to a first principal surface of a first base layer of a first conductive type;
• a buffer layer of the second conductive type provided on a second principal surface opposite to a first principal surface of the second base layer in contact with the first base layer, the buffer layer having a higher impurity concentration in comparison with the second base layer;
• a first collector layer of the second conductive type to contact with a portion of a second principal surface opposite to a first principal surface of the buffer layer in contact with the second base layer, the first collector layer having the higher impurity concentration in comparison with the second base layer;
• a second collector layer of a first conductive type to contact with a portion of the second principal surface of the buffer layer, the second collector layer provided so as to surround the first collector layer, and the second collector layer having the higher impurity concentration in comparison with the first base layer;
• a third collector layer of the first conductive type to contact with a portion of the second principal surface of the buffer layer, the third collector layer provided so as to surround the second collector layer, and the third collector layer having the lower impurity concentration in comparison with the second collector layer;
• a collector electrode connected to a second principal surface opposite to a first principal surface of the first to third collector layers in contact with the buffer layer;
• and
• a fourth collector layer of a second conductive type to contact with the first principal surface of the third collector layer, the fourth collector layer having the lower impurity concentration in comparison with the first collector layer, and the fourth collector layer provided in the buffer layer.