What Is a PIN Photodiode?
A PIN photodiode is a type of photodiode that converts irradiated light into an electrical signal.
There are three main types of photodiodes: PN-type, PIN-type, and APD (Avalanche photodiode).
Compared to PN photodiodes, which consist of PN coupling between P-type and N-type semiconductors, PIN photodiodes have a faster response time from light irradiation to conversion into an electrical signal.
Uses of PIN Photodiodes
PIN photodiodes are the most widely used of all photodiodes due to their high sensitivity and fast response time.
Specifically, PIN photodiodes are used in a wide range of applications, including light-receiving elements in CCD and CMOS sensors in digital cameras, optical pickups for CDs and DVDs, remote control receivers, receivers for optical communication systems, light detectors such as photometers and exposure meters, barcode readers, character readers, automotive sunlight sensors and tunnel sensors, and X-ray detectors and radiation detectors.
Principle of PIN Photodiodes
PIN photodiodes have a structure of a P-type semiconductor and an N-type semiconductor with an insulator I-type semiconductor sandwiched between them.
The P-type semiconductor area is the photosensitive area, the N-type semiconductor side is the substrate side, and the I-type semiconductor area replaces the depletion layer and becomes the light-absorbing area.
When a negative bias is applied to the P layer and a positive bias to the N layer, the holes in the P layer move to the negative side, and the electrons in the N layer move to the positive side, resulting in a depletion layer with almost no carriers in the intermediate layer.
In this state, when light with energy higher than the band gap is irradiated from the P layer side, electrons are photoexcited to become free electrons, and holes are formed in their wake. The holes move to the P layer, resulting in a photocurrent in the PIN photodiodes.
In PIN photodiodes, a reverse bias is applied to the wide depletion layer formed by the I layer, resulting in a faster carrier transfer rate than in PN photodiodes, and thus a faster response time as a photosensor. In addition, the sensitivity is high because the depletion layer, which is the light absorption region, is wide.