## Aim: To draw the I-V characteristic curve of a p-n junction in forward bias and reverse (ordinary and Zener diode)

### Apparatus required:

a) A diode
b) A DC voltage supplier
d) 1k resistor
e)  Multimeter for measuring current and voltage
f) Connecting wires

### Theory:

#### Forward bias characteristics.

When the p -section of the diode is connected to the positive terminal of a battery and n-section is connected to the negative terminal of the battery then junction is said to be forward biased. With an increase in bias voltage, the forward current increases slowly in the beginning and then rapidly. At about 0.7 V for Si diode (0.2 V for Ge), the current increases suddenly. The value of forward bias voltage, at which the forward current increases rapidly, is called cut in voltage or threshold voltage.

#### Reverse bias characteristics.

When the p -section of the diode is connected to the negative terminal of high voltage battery and n-section of the diode is connected to the positive terminal of the same battery, then junction is said to be reverse biased.

When reverse bias voltage increases, initially there is a very small reverse current flow, which remains almost constant with bias. But when reverse bias voltage increases to sufficiently high value, the reverse current suddenly increases to a large value.

This voltage at which breakdown of junction diode occurs (suddenly large current flow) is called Zener breakdown voltage or inverse voltage. The breakdown voltage may start from one volt to several hundred volts, depending upon dopant density and the depletion layer.

### Procedure:

1. First, complete a circuit as shown below with a 1k resistor and a variable
DC input voltage source.

2. We first note the point where the ammeter starts deflecting. We note this
Point and gradually increase the input voltage and take the corresponding

#### For forward-bias:

1.    Make a circuit diagram as shown in the diagram.
2.    Make all connections neat, clean and tight.
3.    Increase the forward-bias voltage
4.    Increase V in steps of 0.1 V and note the corresponding current. Current increases first slowly and then rapidly, till V becomes 0.7 V.
5.    Make V = 0.72 V. The current increases suddenly. This represents the “forward break-down” stage.

#### For reverse-bias:

1. Apply a reverse-bias voltage (VR) of 0.5 V, a feebly reverse current starts flowing.
2. Increase VR in steps of 0.2 V. Current increases first slowly and then rapidly till VR becomes     6V. Note the current... This represents the “reverse break-down” stage. Note the current and take out the key at once.

### Observations:

#### Forward bias:

Forward voltage (V) Forward current(mA)
0.1                                            0.04
0.2                                          0.065
0.3                                               0.1
0.4                                           0.145
0.5                                             0.42
0.6                                               1.5
0.7                                             15.5
0.8

#### Reverse bias:

Reverse voltage(V)          Reverse current(ÂµA)
0.2                                             20
0.4                                              40
0.6                                             60
0.8                                             80
1.0                                           100
1.2                                           115
1.4                                           133
1.6                                           158
1.8                                           180
2.0                                           198
2.2                                           212
2.4                                           238
2.6                                           255
2.8                                           278
3.0                                           295
3.2                                           315
3.4                                           332
3.6                                           348
3.6                                           370
3.8                                           390
4.0                                           410
4.2                                           430
4.4                                           450
4.6                                           468
4.8                                           485
5                                           500

#### Zerer forward bias:

Zener forward voltage(V) Zener forward current(mA)
0.1                                                        0.03
0.2                                                        0.06
0.3                                                        0.1
0.4                                                        0.14
0.5                                                        0.34
0.55                                                     0.72
0.6                                                        1.5
0.7                                                        10

#### Zener reverses bias:

Zener reverse voltage (V) Zener reverse current (mA)
1                                                         0.02
2                                                         0.043
3                                                         0.062
4                                                         0.08
5                                                         0.11
5.2                                                         2
5.5                                                         6.1
5.5                                                         7
5.5                                                         8
5.5                                                         9
5.5                                                         10

#### Precautions:

1. All connections should be neat, clean and tight.
2. Forward-bias voltage beyond breakdown should not be applied.
3. Reverse-bias voltage beyond breakdown should not be applied.