# JEE Main & Advanced Physics Semiconducting Devices Special Purpose Diodes

Special Purpose Diodes

Category : JEE Main & Advanced

(1) Zener diode : It is a highly doped p-n junction which is not damaged by high reverse current. It can operate continuously, without being damaged in the region of reverse background voltage. In the forward bias, the zener diode acts as ordinary diode. It can be used as voltage regulator

(2) Light emitting diode (LED) : Specially designed diodes, which give out light radiations when forward biases. LED'S are made of GaAsp, Gap etc. These are forward biased P-N-junctions which emits spontaneous radiation.

(3) Photo diode: Photodiode is a special type of photo-detector. Suppose an optical photons of frequency n is incident on a semiconductor, such that its energy is greater than the band gap of the semiconductor (i.e.$hv>{{E}_{g}}$) This photon will excite an electron from the valence band to the conduction band leaving a vacancy or hole in the valence band.

Which obviously increase the conductivity of the semiconductor. Therefore, by measuring the change in the conductance (or resistance) of the semiconductor, one can measure the intensity of the optical signal.

(4) Solar cells : It is based on the photovoltic effect. One of the semiconductor region is made so thin that the light incident on it reaches the P-N-junction and gets absorbed. It converts solar energy into electrical energy.

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