| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to provide high-speed response. SOLUTION: An SiGe layer 24 is formed in a P-type silicon layer 12. The Ge density of the SiGe layer 24 is made small near to a PN junction 23. The thickness of a P-type silicon layer 21a is made as thick as a depletion layer on the side of the P-type silicon layer 21. In this case, a carrier generated outside the depletion layer (namely, in a region of P-type silicon layer 21 opposite to the PN junction 23 with respect to the SiGe layer 24 and in the SiGe layer 24) and having no effect from acceleration in an electric field of the depletion layer is enclosed in the SiGe layer 24, where a potential inclination is generated through a gradually narrowed band gap. Then, only a carrier generated in the depletion layer and receiving an effect of acceleration by the electric field of the depletion layer is effectively accelerated in the direction of the PN junction 23, so a decrease in response can be prevented.
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