Semiconductor device provided with photodiode, manufacturing method thereof, and optical disc device

A semiconductor device comprising:

• a heavily doped P-type diffusion layer extending from a surface of a semiconductor substrate to a lightly doped P-type diffusion layer, an impurity concentration of a P-type in the heavily doped P-type diffusion layer being higher than an impurity concentration of the P-type in the lightly doped P-type diffusion layer;
• an N-type semiconductor layer extending from said surface of the semiconductor substrate to a lightly doped P-type semiconductor layer, said impurity concentration of the P-type in the heavily doped P-type diffusion layer being higher than an impurity concentration of the P-type in the lightly doped P-type semiconductor layer;
• a collector diffusion layer region extending from said surface of the semiconductor substrate to said lightly doped P-type diffusion layer, an N-type impurity being within said collector diffusion layer region,
• wherein a portion of the lightly doped P-type diffusion layer is between said heavily doped P-type diffusion layer and said collector diffusion layer region, said portion of the lightly doped P-type diffusion layer touching said surface of the semiconductor substrate,
• wherein said lightly doped P-type semiconductor layer touches said heavily doped P-type diffusion layer and said lightly doped P-type diffusion layer, a portion of the lightly doped P-type semiconductor layer physically separating said N-type semiconductor layer from said heavily doped P-type diffusion layer.