Kalwan Education Societys Arts Commerce and Science College

Kalwan Education Society’s Arts, Commerce and Science College, Kalwan (Manur) Topic: Photodiode Presented by, Miss. A. R. Kothawade

Content: 1. Introduction: 2. Construction and working: 3. I-V characteristics: 4. Advantages and Disadvantages: 5. Application: 6. Comparison of LED and Photodiode

Introduction A Photodiode is p-n junction semiconductor diode which is always operated in the reverse biased condition. Symbol of Photodiode: anode cathode

Construction and working: 1. The light is always focused through a glass lens on the junction of the photodiode. 2. As the photodiode is reverse biased, the depletion region is quit wide, penetrated on both side of the junction. 3. The photons incident on the depletion region will impart their energy to ions present there and generate electron hole pairs.

4. Numbers of electron hole pairs will be dependent on the intensity of light(number of photons). These electrons and holes will be attracted towards the positive and negative terminals respectively of the external source, to constitute the photo current. 5. With increase in the light intensity, more number of electron hole pairs are generated and the photocurrent increases. Thus the photocurrent is proportional to the light intensity.

Advantages 1. It has better frequency response. 2. It has lower noise. 3. High sensitivity. 4. High speed of operation as compared to the LDR.

Disadvantages 1. Dark current increases with temp. 2. Poor temperature stability. 3. It needs offset voltages. 4. It has the small active area. 5. External bias voltage is essential for operation. 6. Amplitification is required as the output current of small magnitude.

Comparison of LED and Photodiode LED 1. It is a Light Emitting Diode. Photodiode 1. It is a Light Detecting Diode. 2. Electrical energy is converted 2. Electric current proportional into light intensity is produced. 3. LED is always forward biased. 3. It is always reverse biased. 4. Ga. As or Ga. As. P are the material used. 4. Silicon is used. 5. Due to recombination of electrons and holes, light is emitted. 5. Due to generation of electron hole pairs, the photocurrent will flow. 6. Radiated power changes 6. Photocurrent and dark due to changes in temperature. current is vary due to changes in temperature. 7. Applications: In 7 segment display as an indicator. 7. In fiber optics , in optocouplers and many other applications.

Application: 1. The most popular application is in event counting. 2. In optical fiber communication system. 3. In photodetector circuit. 4. In solar panel. 5. In optocoupler. 6. In cameras for sensing the light intensity. 7. In light intensity meters.

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