Page 98 - Physics - XII

Semiconductor Electronics:
Semiconductor Electronics:
5 Materials, Devices and
Materials, Devices and
Simple Circuits
Simple Circuits

EXPERIMENT - 9

Aim
To draw the I-V characteristic curve for a p-n junction diode in forward and reverse bias.

Apparatus and Materials Required

A p-n junction diode (or semiconductor diode), a resistor of value 3 Ω, a variable voltage power supply
(0–12 V), a voltmeter (0–12 V), a milliammeter (0–200 mA), a microammeter (0–200 µA), a one-way
key, connecting wires, and a piece of sand paper

Principle/Theory
A p-n junction diode consists of wafers of p-type and n-type semiconductors fused together or grown
on each other.

p n
Fig. 9.1: Symbol of p-n junction diode

Forward and Reverse Biasing of Diode
When an external voltage is applied to a p-n junction, then two types of biasing may take place.
(i) A diode is said to be forward biased, if its p-side is connected to the positive terminal of the battery
and n-side to the negative terminal of the battery.
(ii) A diode is said to be reverse biased, if its p-side is connected to the negative terminal of the battery
and n-side to the positive terminal of the battery.
V
Circuit Diagram to Draw Forward Bias Characteristic
The circuit diagram for a p-n junction diode in forward bias + –
mode is given in Fig. 9.2. With increase in bias voltage, the R
negligible forward current fl ows till the applied voltage crosses p n +
a certain value. After this voltage (about 0.7 V for Si and 0.3 V mA
for Ge), the diode current increases exponentially even for small –
increase in bias voltage. + –

The value of bias voltage at which the forward current increases K E
rapidly is called threshold voltage or cut-in voltage (V ). Fig. 9.2: Forward biasing of p-n
th junction diode

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