P n junction diode

Working of a p-n junction diode.

1. DIODE

2. p- n JUNCTION It is a single crystal of Ge or Si doped in such a manner that one half portion of its acts as p type semiconductor and the other half as n type semiconductor. The term junction implies the boundary or region of transition between n type and p type semiconductor material. Fig: Diode representations: PN-junction model, schematic symbol, physical part.

3. fig:-Diode under forward bias Few characteristics of forward bias:- > Barrier potential decreases. > Movement of majority charge carriers i.e.. holes from p-side to n-side towards the junction. >Effective resistance across the p-n junction decreases. Working of a p- n Junction 1. Forward biasing If the positive terminal of the battery is connected to the p-side and the negative terminal to the n-side , then the p-n junction is said to be forward biased.

4. fig:-Diode under reverse bias Few characteristics of reverse bias:- > Barrier potential across the junction increases. >Movement of majority charge carriers i.e.. electrons away from the junction. >Effective resistance across the p-n junction increases. 2. Reverse biasing If the positive terminal of a battery is connected to the n-side and the negative terminal to the p-side , then the p-n junction is said to be reversed biased.

5. V-I characteristics of a p- n junction diode:- 1.Forwad bias characteristics:- The p-n junction diode is connected to a potentiometer (or rheostat) so that voltage applied can be changed. For different values of voltages, the value of current is noted. A graph is plotted between V and I. This voltage-current graph is called Forward characteristics.

6. Features of Graph: 1.The V-I graph is not straight line i.e.. A junction diode doesn’t follow Ohm’s law. 2 .Initially current increases very slowly almost negligibly , till the voltage across the diode crosses a certain value , called threshold-voltage or cut-in voltage . The value of cut –in voltage is about 0.2 for a Ge diode and 0.7 for a Si diode. 3.After the cut-in voltage, the diode current increases rapidly(exponentially), even for a very small increase in the bias voltage.

7. 2.Reverse bias characteristics:- The p-n junction diode is connected to a potentiometer(or rheostat) so that the voltage the diode can be changed. For different values of voltage, the value of current is noted . A graph is plotted between V and I. This voltage-current graph is called Reverse characteristics.

8. Features of Graph:- 1. When the diode is reverse biased , the reverse bias voltage, the reverse bias voltage produce very less current, about a few microamperes which almost remain constant with bias .This small current is called R everse saturation current . 2.When the reverse voltage across p-n junction reaches a sufficiently high value, the reverse current increases to a large value. This voltage at which breakdown of junction takes place is called Zener breakdown voltage or peak-inverse voltage of the diode.

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