ELECTROSTATIC DISCHARGE PROTECTING DEVICE HAVING HETERO-JUNCTION STRUCTURE

PROBLEM TO BE SOLVED: To achieve higher speed turning on of a parasitic bipolar transistor by providing a material layer with a potential lower than that of the silicon substrate in the silicon substrate between the source and the drain. SOLUTION: A material layer 50 with a potential lower than that of the silicon substrate 10 is formed in the silicon substrate 10 between the source 20 and the drain 30. This material layer 50 serves to collect holes from among electrons and holes generated by a strong electric field in the drain region produced by an electrostatic discharge pulse. Further, the material layer 50 is formed of a hetero-junction structure. Therefore, the material layer 50 has an energy gap smaller than that of the silicon forming the substrate 10 so that it can form a quantum well with a potential lower than that of the substrate 10 and it can rapidly drive a parasitic bipolar transistor because the electrons and holes of germanium have a large mobility. Thus, higher speed turning ON of the parasitic bipolar transistor can be achieved and a overcurrent can be prevented from flowing into the chip.