To study the characteristics of PN Junction diode under forward and reverse bias conditions.

Aim

To study the characteristics of PN Junction diode under forward and reverse bias conditions.

Apparatus Required:

Components Required:

Theory:

A PN junction diode is a two terminal semiconducting device. It conducts only in one direction (only on forward biasing). Forward Bias On forward biasing, initially no current flows due to barrier potential. As the applied potential exceeds the barrier potential the charge carriers gain sufficient energy to cross the potential barrier and hence enter the other region. The holes, which are majority carriers in the P-region, become minority carriers on entering the N-regions, and electrons which are the majority carriers in the N-region, become minority carriers on entering the P-region. This injection of minority carriers results in the current flow, opposite to the direction of electron movement.

Reverse Bias

On reverse biasing, the majority charge carriers are attracted towards the terminals due to the applied potential resulting in the widening of the depletion region. Since the charge carriers are pushed towards the terminals no current flows in the device due to majority charge carriers. There will be some current in the device due to the thermally generated minority carriers. The generation of such carriers is independent of the applied potential and hence the current is constant for all increasing reverse potential. This current is referred to as Reverse Saturation Current (IO) and it increases with temperature. When the applied reverse voltage is increased beyond the certain limit, it results in breakdown. During breakdown, the diode current increases tremendously.

Procedure Forward Bias

1. Connect the circuit as per the diagram.
2. Vary the applied voltage V in steps of 0.1V.
3. Note down the corresponding Ammeter readings I.
4. Plot a graph between V & I

Observations

1. Find the d.c (static) resistance = V/I.
2. Find the a.c (dynamic) resistance r = δV / δI (r = ΔV/ΔI)= V₂-V₁I₂-I₁
3. Find the forward voltage drop [Hint: it is equal to 0.7 for Si and 0.3 for Ge]

Reverse Bias

1. Connect the circuit as per the diagram
2. Vary the applied voltage V in steps of 1.0V.
3. Note down the corresponding Ammeter readings I.

4. Plot a graph between V & I
5. Find the a.c (dynamic) resistance r= δV/δI

Formula for Reverse Saturation Current (I _O):

I= I₀(e ^V/ηVT-1)

where I is forward (or reverse) diode current, I ₀is reverse saturation current, V is external voltage (+ve for forward bias & -ve for reverser bias),η is constant number (1 for Silicon and 2 for Germanium), V _T is the volt-equivalent of temperature ( T/11600 ) and T is temperature in Kelvin.

Circuit Diagram

Forward Bias

Specification for 1N4001: Silicon Diode

Peak Inverse Voltage: 50 V

I _dc=1A.

Maximum forward voltage drop at 1 Amp is 1.1 volts

Maximum reverse current at 50 volts is 5μA

Tabular Column

Forward Bias

Reverse Bias

Model Graph

Result