Semiconductor Diode: Class 12 Physics Notes, Definition, Working Principle, Types & Examples

The working principle of semiconductor diode is based on p-n junction.The one side of junction is p-type and other is n-types. The p-type region contains holes (excess positive charge) while, n-types region is contains electrons (excess negative charge carriers). When an external voltage is connected to the p-n junctions, holes difuses from the p-type and electrons from n-type region. During the movement of charges a depletion region is formed at junction. This region creates an emf (internal electric field) that opposes the further flow of charges. 

The behaviour of the diode depends on the polarirty: in forwards bias, barrier is reduced and allow the flow of current in one direction. While in reverse bias, barrier is widen which prevent the flow of current. Below is the detailed explanation of Semiconductor diode working priciple in forward bias and reverse bias.

Forward Biasing

In formaward biasing, external voltage is connected to the p-n junction in such that $p$ -region is connected to the positive terminal and $n$ -region is connected to the negative terminal as shown in the figure.

Forward-Biased Characteristics:

In the circuit connection setup (as shown in the figure), p-n diode is connected through a potential-divider arrangement which enables to change the applied voltage. The voltage across the diode is measured through voltmeter (V) while, millimeter (mA) measure the current.

 

• In the forward bias current is increased from a low value.
• The corresponding current is noted.
• A graph is then plotted between voltage and current, resulting curve OAB is the forward characteristic of the diode.

Behaviour:

• Initially, the current through the diode is almost zero (0) due to potential barrier (about 0.3 V for $\mathrm{G}\mathrm{e}\mathrm{p}-\mathrm{n}$ junction and about 0.7 V for the Si junction).
• When the applied voltage is increased, current increases slowly and non-linearly until the voltage exceeds the potential barrier (curve OA).
• Current increases rapidly and alomost linearly (line AB) beyond barrier voltage, this indicates diode now behave like an ordinary conductor.
• This is represented by the straight-line part $AB$ of the characteristic. If this straight line is projected back. It intersects the voltage axis at the barrier potential voltage.

Note :

(i) The depletion layer decreases in forward bias.
(ii) The resistance offered in the forward bias is ${\mathrm{R}}_{\text{Forward}}\approx 10\mathrm{\Omega }-25\mathrm{\Omega }$
(iii) Forward bias opposes the potential barrier and for $V>V_B$  a forward current is set up across the junction.
(iv) Cut-in (Knee) voltage: The voltage at which the current starts to increase rapidily (≈ 0.3 V for Ge, ≈ 0.7 V for Si).

Reverse Biasing 

A junction diode is reverse-biased when the positive terminal of the external battery is connected to the n-region and the negative terminal to the p -region of the diode (Fig.). This confiuration of diode causes depletion region to widen the barrier and prevent the flow of current.

Below is the types of semiconductor alongwith their applications.

Types of Semiconductor Diode	Applications
Zener Diode	Stabilisation of current and voltage
Rectifier Diode	Retification of AC to DC
Photodiode	Work as photo detector
Tunnel Diode	Used in negative dynamic resistance region
Switching Diode	Fast switching of electrical signals
Variable capacitance diode	Used in reversed biased
LED	Emitting infrared light spectrum

The semiconductor is a material that allows the flow of current within it. Silicon is the most commonly used material in the semiconductor. Below are the examples of semiconductors and their uses.

Examples of Semiconductors:

• Silicon (Si): Used in solar cells, transistors and microchips.
• Gallium Arsenide (GaAs): Used in laser diode, microwave integrated circuits, and high-speed electronics.
• Gallium Nitride (GaN): Used in high-frequency devices and power electronics
• Germanium (Ge): Used in infrared detectors.
• Indium Phosphide (InP): Used in optoelectronics and high-speed electronics.
• Zinc Oxide (ZnO): Used in solar cells, sensors and various applications.