| 摘要 |
An optical semiconductor device is provided with a low concentration p-type silicon substrate (1); a low dopant concentration n-type epitaxial layer (second epitaxial layer) (26); a low dopant concentration p-type anode layer (27); a high concentration n-type cathode contact layer (9); a photodiode (2) made of the anode layer (27) and the cathode contact layer (9); and an NPN transistor (3) formed on the n-type epitaxial layer (26). The anode can be substantially completely depleted in the case where the anode layer (27) has its dopant concentration peak in the vicinity of the interface between the silicon substrate (1) and the n-type epitaxial layer (26). Therefore, high speed and high light receiving sensitivity characteristics can be obtained, and further, any influence of auto-doping from peripheral embedding layers can be controlled, so that a depletion layer can be stably formed in the anode. Thus, a photodiode characterized in its high speed and high light receiving sensitivity for short wavelength light and a transistor characterized in its high speed can be mounted on the same semiconductor substrate.
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