With recent increases in the driving frequencies of CPUs (for example, up to 10 GHz or more), optical interconnection arts, for transmitting signals within a system device or among devices by the sending and receiving of light, have come to be noted. Optical semiconductor devices, such as semiconductor photodetectors and semiconductor light emitting devices, are used in such optical interconnection arts.
Among semiconductor photodetectors, there are known back-illuminated semiconductor photodetectors, which have a semiconductor substrate and with which a plurality of compound semiconductor layers are formed on a back surface that opposes a light-incident surface of the semiconductor substrate (see, for example, Patent Documents 1 to 3). With the semiconductor photodetectors described in these Patent Documents 1 to 3, a substrate portion corresponding to a photosensitive portion is thinned partially and a thick portion is formed so as to surround this substrate portion for the following reasons. A first reason is to prevent optical signal degradation or extinction due to light absorption by the semiconductor photodetector from becoming damaged or broken when the semiconductor photodetector is mounted by wire bonding or bump bonding onto an external substrate, etc.
Patent Document 1: Japanese Patent Application Laid-Open No. H3-104287
Patent Document 2: Japanese Patent Application Laid-Open No. H6-296035
Patent Document 3: Japanese Patent, Application Laid-Open No. 2002-353564