Venugopala Rao Dept of CSE SSE, Mukka Electronic Circuits 10CS32

Optoelectronic devices 2/27/2016 Venugopala Rao A S, SSE Mukka 2 Photodiode types: There are various types of photodiodes depending on the construction. PN Photodiodes PIN Photodiodes Schottky type Photodiodes Avalanche Photodiodes. PN Photodiodes Comprises of PN junction as shown

Optoelectronic devices 2/27/2016 Venugopala Rao A S, SSE Mukka 3 When light with sufficient energy is made to fall on diode, photoinduced carriers are generated. These include electrons in the conduction band of P - type material and holes in the valence band of the N-type material. When photodiode is reverse biased, photoinduced electrons move downwards from P-type material to N-type material.

Optoelectronic devices 2/27/2016 Venugopala Rao A S, SSE Mukka 4 Similar action will take place w.r.t. holes and they move from N-side to P-side Shorter wavelength signals are absorbed at the surface itself an longer wavelength signals penetrate into the diode. Applications: Used in medical instrumentation, analytical instrumentation etc PIN diode: Here additional high resistance layer is added between P and N layers as shown

Optoelectronic devices 2/27/2016 Venugopala Rao A S, SSE Mukka 5 This coat reduces the diffusion time and hence increases the response time. Low capacitance being major feature of PIN photodiodes, it offers large bandwidth. Hence it is useful for high speed photometry and optical communication applications. Schottky diode: In these, there is a thin gold coating on the N-type material to ensure the Schottky effect. This diode has better performance under UV radiation. Avalanche Photodiode: These are high speed high sensitivity photodiodes which makes use of internal gain mechanism by applying higher reverse voltages as compared to PIN diodes.

Optoelectronic devices 2/27/2016 Venugopala Rao A S, SSE Mukka 6 APDs are constructed with uniform junction which exhibits avalanche effect at about 30V to 200V. Electron-hole pair generated due to incident light are accelerated applied electric field. This ensures that, new electrons are moved to conduction band. Thereby current increases rapidly. APD is also fast responsive similar to PIN photodiode. Offer higher SNR and hence used in sensitive applications like long distance OFC communication

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