characteristic curve for three diodes

8/6/2019 Characteristic Curve for Three Diodes

1/15


2/15


3/15

.

Experiment :C-8

Drawing of the characteristic curve for three semiconducter diodes.

Submitted to Mr. Golam Dastegir Al-Quaderi and

Dr. Ratan Chandra Gosh

Submitted by Muhammed Mehedi Hassan Group A ;Batch-09 Second

Year, RollSH 236 Student of Physics Department, Uinversity of Dhaka.

Date ofexperiment May 03,2011. Date of submission July 04,2011.

1


4/15


5/15


6/15

Experiment : Drawing of the characteristic curve for three semiconducter diodes. Theory : One of the

crucial keys to solid state electronics is the nature of the P-N junction. When p-type and n-type materials

are placed in contact with each other, the junction behaves very differently than either type of material

alone. Specif- ically, current will flow readily in one direction (forward biased) but not in the other (reverse

biased), creating the basic diode. This non-reversing behavior arises from the nature of the charge

transport process in the two types of materials. In the p-type region there are holes from the acceptor

impurities and in the n-type region there are extra electrons.

Figure 8.1 Forward and reverse bias of P-N junction diodes.

When a p-n junction is formed, some of the electrons from the n-region which have reached the

conduction band are free to diffuse across the junction and combine with holes.

Filling a hole makes a negative ion and leaves behind a positive ion on the n-side. A space charge

builds up, creating a depletion region which inhibits any further electron transfer unless it is helped by

putting a forward bias on Equilibrium of junction.

With the application of sufficient reverse voltage, a p-n junction will experi- ence a rapid avalanche

breakdown and conduct current in the reverse direction. Valence electrons which break free under the

influence of the applied electric field can be accelerated enough that they can knock loose other electrons

and the subsequent collisions quickly become an avalanche. When this process is taking place, very

small changes in voltage can cause very large changes in current. The breakdown process depends

upon the applied electric field, so by changing the thickness of the layer to which the voltage is applied,

zener diodes can be formed which break down at voltages from about 4 volts to several hundred volts.

These characteristics can be shown by suitable graph.

Apparatus : A circuit board,three different diodes and some connecting wires.

2


7/15


8/15


9/15

Table -8.1:Reading for the forward connection:

Diode -1 Diode -2 Diode -3 Voltage Current Voltage Current Voltage Current V mA V mA V mA 0.00 0.00

0.00 0.00 0.00 0.00 0.10 0.00 0.10 0.01 0.10 0.00 0.15 0.00 0.12 0.02 0.15 0.00 0.20 0.00 0.15 0.05 0.20

0.00 0.21 0.00 0.16 0.06 0.25 0.00 0.27 0.00 0.18 0.08 0.30 0.00 0.30 0.00 0.19 0.11 0.35 0.00 0.35 0.00

0.21 0.12 0.40 0.00 0.40 0.00 0.22 0.14 0.45 0.00 0.42 0.01 0.23 0.15 0.50 0.00 0.46 0.01 0.24 0.17 0.600.00 0.51 0.02 0.25 0.19 0.65 0.00 0.56 0.03 0.26 0.20 0.70 0.00 0.60 0.04 0.27 0.21 0.75 0.00 0.61 0.05

0.28 0.23 0.80 0.01 0.62 0.06 0.29 0.25 0.81 0.02 0.64 0.06 0.30 0.27 0.82 0.03 0.65 0.07 0.31 0.30 0.85

0.06 0.66 0.07 0.32 0.32 0.89 0.08 0.67 0.07 0.33 0.34 0.92 0.12 0.68 0.08 0.40 0.50 0.95 0.21 0.69 0.19

0.45 0.64 0.97 0.25 0.70 0.28 0.50 0.74 0.98 0.28 0.71 0.37 0.60 1.03 1.00 0.34 0.75 0.54 0.70 1.34 1.01

0.42 0.80 0.90 0.80 1.62 1.03 0.49 0.90 3.48 0.90 1.94 1.05 0.67 1.00 8.12 1.00 2.29 1.10 0.82

3


10/15


11/15


12/15

Table -8.2:Reading for the reverse connection:

Diode -1 Diode -2 Diode -3 Voltage Current Voltage Current Voltage Current V A V A V A 0.00 0.00

0.00 0.00 0.00 0.00 0.05 0.00 0.03 1.50 0.30 0.00 0.10 0.00 0.05 2.30 0.50 0.00 0.15 0.00 0.07 2.60 1.50

0.00 0.20 0.00 0.09 2.90 2.00 0.00 0.25 0.00 0.10 3.00 2.50 0.00 0.30 0.00 0.15 3.50 3.00 0.00 0.35 0.00

0.18 3.70 3.21 0.00 0.40 0.00 0.20 3.85 3.30 0.00 0.45 0.00 0.25 4.00 3.50 0.10 0.50 0.00 0.30 4.10 4.000.10 0.55 0.00 0.35 4.20 4.07 0.20 0.60 0.00 0.40 4.40 4.13 0.30 1.00 0.00 0.45 4.60 4.20 0.40 1.50 0.00

0.50 4.80 4.25 0.45 2.00 0.00 0.55 5.00 4.30 0.51 3.00 0.00 0.60 5.10 4.40 0.60 4.00 0.00 0.65 5.30 4.50

0.70 5.00 0.00 0.70 5.40 4.60 1.00 6.00 0.00 0.75 5.50 4.70 1.30 7.00 0.00 0.80 5.60 4.80 1.60 8.00 0.00

0.85 5.70 4.90 2.00 9.00 0.00 0.90 5.80 5.00 2.50 10.00 0.00 0.95 6.10 5.30 3.80 - - 1.00 6.50 5.50 6.00 -

- 1.20 6.90 6.00 16.00

Calculation : Diode equation

I = I

o

(eqv/nkT 1) lnI = lnI

o

+ ln(eqv/nkT 1) Therefore lnI = lnI

o

+ qv/nkT.........(i) Assume that: eqv/nkT >> 1 qv/nkT >> 0 here n

Si

= 2 and n

Ge

= 1 Therefore ln(I/I

o

) = qv/nkT Theoritically, q/k= 1.381023JK1

1.61019C

= 11594.2CJ1K

4


13/15


14/15


15/15

We know the equation for straight line in x-y plane is:

y=mx+c..........(ii)

Comparing equation (i) and (ii) we get ,

slope =q/nkT..........(iii)

So q/k can be determined for the diodes

For diode-1 slope is 11.81 so,

q/k=11.81 2 306CKJ1 = 7227.72CKJ1

For diode-2 slope is 5.04 so,

q/k=5.04 1 306CKJ1 = 1512CKJ1

Percentage of error for diode-1(Silicon)=|115947227

11594

| 100% = 37.6%

Percentage of error for diode-2(Germenium)=|115941512

11594

| 100%=86.9% Discussion :

We have used three different diode and from the graph the material of the diode can be figure out.

Here the break down voltage for first diode is nearly 0.7V , by theoritical knowledge this is the break down

voltage for Silicon. For the second diode it is nearly 0.3V, which refers to a Germenium diode. And the

third is a Zener diode, whose charcteristic knee voltage is -4.0V.

For these intrinsic semiconductor(silicon and germanium),this charcteristics can be explained by the

band thoery.According that the Fermi level is essentially halfway between the valence and conduction

bands. Although no conduction occurs at 0 K, at higher temperatures a finite number of electrons can

reach the conduction band and provide some current. In doped semiconductors, extra energy levels areadded.The application of band theory to n-type and p-type semiconductors shows that extra levels have

been added by the impurities. In n-type material there are electron energy levels near the top of the band

gap so that they can be easily excited into the conduction band. In p-type material, extra holes in the

band gap allow excitation of valence band electrons, leaving mobile holes in the valence band.

The nature of the p-n junction is that it will conduct current in the forward direction but not in the

reverse direction. It is therefore a basic tool for rectification in the building of DC power supplies.

5

characteristic curve for three diodes

Documents