PHOTOTRANSISTOR

PURPOSE:To obtain the phototransistor capable of responding at high speed by concavely hollowing out one end of a base region flatly and forming an emitter electrode pad to the concave section when an emitter region is shaped into the base region and the pad connected to the emitter region is molded. CONSTITUTION:The phototransistor with planer type PIN structure is formed in such a manner that an n type layer 2 is grown onto an n type semiconductor substrate 1 as a collector in epitaxial shape, the p type base region 3 is diffused and formed into the layer 2 and the n type emitter region 4 is further shaped into the region 3. The whole surface is coated with a transparent protective film 9, windows are bored while being made correspond to the regions 3, 4, and an electrode pad 10 is attached to the region 3 and Al wiring 8 to the region 4 through a contact hole 7. The wiring 8 is connected to the emitter electrode pad 6, but the pad 6 is positioned into the concave section 5 flatly shaped to the base region and shortens a distance between the region 4 and the pad 6 at that time. Accordingly, a predetermined depletion layer 12 is formed into the layer 2, and the speed of response is increased.