AIM: To draw the I-V characteristic curve of a p-n junction in forward bias and reverse bias
• Apparatus: (1) pn-junction diode (2) two batteries of emf 2 volt and 12 volt (3) one rheostat (4) two
voltmeter of ranges 0-2 volt and 0-10 volt (5) one milliammeter of range 0-100 mA (6) one
microammeter of range 0-1A (7) one way key (8) connecting wires.
• Theory:
A p-n-junction is forward biased when the p-end of the junction is connected to the
positive terminal and the n-end is connected to the negative terminal of the battery.
When the forward bias voltage is increased, the forward current increases
At first very slowly. When the voltage crosses the value around 0.7 volt for Si
crystal and 0.3 volt for Ge crystal, the current begins to increases very rapidly.
If the current (I) is plotted against the forward voltage (V) we get the
Characteristic curve in forward bias as show in Fig:1
Fig: 1
If the p-end of the junction is connected to the negative terminal of the battery and n-end to the positive
terminal, the p-n junction is to be reverse-biased.
When the reverse bias is increased slowly, a small current flow in
The opposite direction. The current does not change when the reverse
bias is increased. When the reverse voltage is increased to a very high
Value, the reverse current increases suddenly to a
Very large value
Fig:2
The reverse current against reverse voltage characteristic curve for a reverse-biased p-n junction is show in
Fig: 2
• Procedure
1.
2.
3.
4.
5.
6.
7.
(a) For forward bias:
The connections are made as shown in Fig. (a). The p-side of the diode is to be connected to the
positive terminal of the battery.
Name of diode, maximum forward current and maximum reverse voltage are noted from manual.
Least count and zero error of the voltmeter and milliammeter are to be noted.
The knob of the rheostat is to be rotated anticlockwise at the extreme end. The reading of the
milliammeter and voltmeter would be zero. The readings are to be noted.
Now The knob is to be rotated clockwise so that the reading in the voltmeter be 0.1V. The current
should be zero then readings are to be noted.
The step 5 is to repeated and the voltage will be increased by 0.1 V. The voltage and current are noted
at each step. When the voltage will be 0.7 V for Si-diode (0.3 V for Ge-diode, the current will be
increased suddenly. The voltage may be increased to the maximum forward voltage after increasing
the voltage by 0.2 V.
I-V graph will be plotted.
(b)
For reverse bias
1.The connections are made as shown in Fig.b. The p-side of the diode is to be connected to the
negative terminal of the battery.
2. Step-2 and 3 for forward bias is to be followed.
3. The knob of the rheostat is to be moved anticlockwise to the extreme end. The reading of the
milliammeter and voltmeter would be zero. The readings are to be noted
4. The knob of the jokey is to be moved clockwise to apply a small reverse voltage and the reverse
voltage is to be increased in small steps. In each step the reading of voltmeter and microammeter is to
noted.
• EXPERIMENTAL RESULTS
(a)For forward bias
Range of voltmeter= 0 to 2 volt
Least count= 0.04 volt
Range of ammeter= 0 to 100 mA
Least count= 2 mA
No. of observations
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
(b) For reverse bias
Range of voltmeter= 0 to 10 volt
Least count= 0.2 volt
Range of ammeter= 0 to 1mA
Least count= 0.02 mA
Forward voltage (in volt)
Forward current (in mA)
0
0.08
0.16
0.24
0.32
0.40
0.48
0.56
0.64
0.72
0.80
0.88
1.08
1.16
1.24
1.32
1.36
0
0
0
0
0
0
0
4
10
18
26
40
52
64
78
90
100
No. of observations
Reverse voltage (in volt)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
0
0.4
0.8
1.2
1.6
2.0
2.4
2.8
3.2
3.6
4.0
4.4
4.8
5.2
5.6
6.0
6.4
6.8
7.2
7.6
8.0
8.4
8.8
9.2
9.6
Reverse current (in mA)
0
0
0
0
0.02
0.04
0.08
0.10
0.14
0.18
0.22
0.24
0.28
0.32
0.36
0.40
0.44
0.48
0.52
0.56
0.62
0.66
0.70
0.74
0.78