2. History & Theory
Photodiode technology developments came out of the basic developments of the PN junction
diode that started in the 1940s. Applications for the use of the PN junction diode were found
outside the basic use of rectifying signals.
Photodiode technology was refined in the 1950s and in the latter part of that decade the PIN
photodiode was developed. Light absorption in the wide depletion area of the PIN structure was
first investigated in a paper published in 1959 by Gartner. Although silicon has been the favored
material for photodiodes, germanium can also be used, and its use was first demonstrated in 1962
by Riesz.
3. Photodiode
A photodiode is a kind of light detector, which involves the conversion of light into voltage
or current, based on the mode of operation of the device.
4. Operation
A photodiode is designed to operate in reverse bias.
A photodiode is a semi-conductor device, with a p-n junction and an intrinsic layer between p and n
layers. It produces photocurrent by generating electron-hole pairs, due to the absorption of light in
the intrinsic or depletion region. The photocurrent thus generated is proportional to the absorbed
light intensity.
8. Why Use Photodiodes?
Usable with almost any visible or near infrared light source such as LEDs, fluorescent,
incandescent bulbs, lasers sources ,sunlight; etc.
Fast response times.
Low noise.
Lightweight.
Low cost.
9. Applications of Photodiode
Photodiodes are used in many different types of circuits and applications. Here are a
few examples of where photodiodes have been used.
Communications
• Fiber Optic Links
• Optical Communications
• Optical Remote Control
Safety Equipment
• Smoke Detectors
• Flame Monitors
• Security Inspection Equipment - Airport X ray
• Intruder Alert - Security System
10. Applications of Photodiode
Industry
• Bar Code Scanners
• Light Pens
• Brightness Controls
• Encoders
• Position Sensors
• Surveying Instruments
• Copiers - Density of Toner
