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EXPERIMENT NO:8 DATE:

AIM OF THE EXPERIMENT:

To study how to observe Hall Effect in semiconductor.

APPARATUS REQUIRED:

1.  Electromagnets 

2.  Power supply (for electromagnets) 

3.  Gauss meter (for measuring magnetic flux) 

4.  Germanium crystal maounted 

5.  Constant current supply (for crystal) 

THEORY:

Hall Effect is a magneto-electric effect.If a current µx¶ passes in X-direction of the crystal and a

magnetic field Bz is applied in Z-direction,then a potential difference,called the Hall potential

difference ,is produced in Y-direction.The sign of Hall potential depends on the nature of charge

carriers,Thus by noting the directions of hall potential and the magnetic field,the nature of charge

carriers may be determined by the use of Fleming Left Hand rule.

Hall Coefficient(R):

R=

 

Carrier density (n):

R=

=> n=

 

Carrier Mobility:

For degenerate semiconductor i.e. when one carrier dominates,

 R 

BRIEF DESCRIPTION OF THE APPARATUS

Electromagnets:

It is a double coiled Electromagnet,the field of which is variable by moving mild steel rods.the

gap of magnetic poles can be adjusted by rotating knobs given at the end of the electromagnets.

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Electromagnet is mounted on the wooden board with a rod fitted crystal and hail probe so that it

can easy to operate.Two terminals are provided for connecting supply to the electromagnets.

Power supply for electromagnets:

The power supply consist 1. Current meter 

2.A.C/ON switch to on the power 

3.Level knob to control current in electromagnets

The magnetic strength can be variable by this knob,output terminals are to take output from

 power supply to connect it to electromagnets.

Power supply for crystal:

It is an constant current power supply 0-20 milliamp.Variation in the current are achieved by a potentiometer.The supply is a highly regulated and practically ripple free d.c. source.The current

is measured by the digital Panel meter.

Ge. Crystal:

Ge. Single crystal with four spring type pressure contacts is mounted on a sunmica decorated

Bakelite strip.Four leads provided for connections with measuring devices.

The exact value of thickness and resistivity is provided on the crystal strip.

CONNECTION PROCEDURE:

1.  Connect Electromagnets with terminals of the Power Supply as shown in the given figure

and connect Ge. Crystal probe with constant current power supply.

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2.  Small plugs are for Hall Voltage ,other is for current.

3.  Plug power supplies in AC mains 220v 50Hz.

4.  Magnetic field generated is sensed by the help of Hall Probe connected with Gause

meter.It is directly calibrated in terms of Gauses.

SPECIFICATION OF CRYSTAL:

WIDTH :

BREDTH:

THICKNESS:

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PROCEDURE:

1.  Connect the Hall crystal to constant current power supply in their respective sockets.

2.  Switch ON the Power Supply and adjust the current Ix(mA).

3.  There may be some voltage in the mV meter even outside the magnetic field.This is due

to imperfect alignment of four contacts of Ge.crystal and is generally known as µZero

Field Potential¶. In case its value is comparable to Hall voltage it should be adjusted to a

minimum possible. In all cases,this error should be subtracted from the Hall voltage

reading.

4.   Now place the probe in the magnetic field as shown in figure and switch on the

electromagnet power supply and adjust the current to any desired value.Rotate the Ge.

Crystal probe till it become perpendicular to magnetic field.Hall voltage VH will be

maximum in this adjustment.

5.  Measure Hall voltage for both the directions of current and magnetic field (i.e. four 

observations for a particular value of current and magnetic field).

6.  Change the value of Ix in steps and note corresponding values of Ix and VH.Take many

readings.Then plot a graph in VH and Ix values.It will be straight line whose slop will be

given by VH/Ix.

7.  Measure the magnetic field,B with a gauss meter.

PECAUTION:

1.  Handle the Ge. Crystal with care ,it can break.

2.  Handle the Hall probe of Gauss meter with care, it may be damage in mishandling.

3.  Do use Electromagnets continus at full current.It may start heat.

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OBSERVATION TABLE:

Magnetic field:

Sl.  No. Hall Current(Ix) Hall Voltage (VH)

1

2

3

4

5

6

CALCULATION:

1.  From the graph Hall voltage Vs. magnetic field calculate Hall coefficient.

2.  Determine the type of majority charge carriers,i.e. whether the crystal is n-type or p-type.

3.  Calculate charge carriers density from the relation

R=

=> n=

 

4. Calculate carrier mobility using the formula  R  

CONCLUSION:

Name:

Regd No.

MTECH,AE&I,

1ST

SEM