Question

From the following semi-conductor devices, operates in forward bias only. (A) Varactar diode (B) Zenger diode (C) Light emitting diode (D) photo-diode

Short answer

The Light Emitting Diode (LED) is the only device among the given options that operates in forward bias only. Therefore, the correct answer is (C) Light Emitting Diode.

Step-by-step solution

Understanding Semiconductor Devices

A semiconductor device's operation, including diodes, is defined by its P-N junction properties. The properties change depending on whether the device is in forward bias or reverse bias. Forward bias occurs when the P-type semiconductor (anode) is connected to the positive terminal and the N-type semiconductor (cathode) is connected to the negative terminal of the power supply.

Analysing the Varactor Diode

A Varactor diode is a type of diode where the PN junction capacitance can be varied by applying a voltage. Varactor diodes are used as voltage-controlled capacitors in frequency tuning circuits. They work in reverse bias, and the capacitance is inversely proportional to the depletion layer width.

Analysing the Zener Diode

Zener diodes are specifically designed to operate in reverse bias. When a Zener diode is adequately reverse-biased, it causes a controlled breakdown that allows current to keep flowing. This property is used for functions like voltage regulation in electronic circuits.

Analysing the Light Emitting Diode (LED)

Light Emitting Diodes (LEDs) operate only in forward bias. When forward biased, an LED emits light corresponding to the energy bandgap of the semiconductor material used in P-N junction formation. So, LEDs function in forward bias mode only.

Analysing the Photo Diode

A photodiode primarily functions in reverse bias mode. It absorbs light and generates a photocurrent due to the photovoltaic effect. The photocurrent's magnitude depends on the light intensity incident on the diode.

Summarizing the Findings

Based on our analysis, the Varactor diode, Zener diode, and Photodiode operate in reverse bias. Only the Light Emitting Diode (LED) consistently operates in forward bias. Thus, the correct answer is (C) Light Emitting Diode.