How Photodiode Works

• Photodiode: A thin n-type semiconductor sandwiched with a thicker p-type semiconductor.
• N-side is cathode, p-side is anode.
• Upon illumination, a # of photons pass from the n-side and into the p-side of
photodiode.
– Some photons making it into p-side collide with bound electrons within psemiconductor, ejecting them and creating holes.
– If these collisions are close to the pninterface, the ejected electrons cross the
junction, yielding extra electrons on the n-side and extra holes on the p-side.
– Segregation of +ve and  -ve charges leads to a potential difference across the
pn-junction.
– When a wire is connected between the cathode and anode, a conventionally
positive current flow from the anode to cathode