Abstract: A light detector is configured such that a light receiving portion having APDs and a peripheral portion are provided on a first principal surface of a p-type semiconductor substrate, and further includes a back electrode provided on a second principal surface of the semiconductor substrate and a p-type first separation portion provided between the light receiving portion and the peripheral portion. The APD has, on a first principal surface side, an n-type region and a p-epitaxial layer contacting the n-type region in a Z-direction. The peripheral portion has an n-type MISFET provided at a p-well and an n-well provided to surround entire side and bottom portions of the p-well.

Abstract: Herein disclosed is a method for ultrasonic flaw detection of T-welded portion of steel product. The method comprises: maintaining the flange portion horizontally, making convergent ultrasonic beams incident on the flange portion vertically to the top face of the flange portion through a medium, scanning the incident beams transversely of the welded portion, detecting ultrasonic echo from a depth corresponding to the bottom face thickness of the flange portion, and comparing the level of said ultrasonic echo with a predetermined threshold value. Disclosed also is an apparatus for carry out the above method. These method and apparatus are suited particularly to the on-line flaw detection of the welded shape steel.