| 摘要 |
A P-type epitaxial silicon layer is formed between an N-type epitaxial layer and a P+-type semiconductor substrate. An impurity concentration profile is formed in at least one region of the P-type epitaxial silicon layer to decrease with an increase in distance from the substrate and toward the N-type epitaxial layer. A depletion layer is formed as a function region (P-N junction) between the P-type epitaxial silicon layer and the N-type epitaxial layer. Carriers are generated when light is incident on the depletion layer. Carriers are also generated in a region of the P-type layer deeper than the depletion layer. A self-electric field is formed in the P-type epitaxial silicon layer by the impurity concentration profile, which is lowest at the junction. The carriers generated in this manner are accelerated by the self-electric field and flow rapidly into the function region. As a result, an optical semiconductor device according to the present invention has good response characteristics.
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