A
photodiode is a semiconductor device that converts
light into
current. The current is generated when photons are absorbed in the photodiode. A small amount of current is also produced when no light is present. Photodiodes may contain
optical filters, built-in lenses, and may have large or small surface areas. Photodiodes usually have a slower response time as their surface area increases. The common, traditional
solar cell used to generate electric
solar power is a large area photodiode.