Hall Devices

HALL DEVICES

The device which uses the hall effect for its application is known as Hall device.

There are three types of Hall devices.

They are

(a) Gauss Meter

(b) Electronic Multiplier

(c) Electronic Wattmeter

(a) Gauss Meter

The Hall voltage V_H = R_H B_Z I_x / t In this, V_H  ∝ B_Z for a given hall element; R_H and t are constant. The current I through Hall element is also kept constant.

This principle is used in Gauss meter. It is used for measuring magnetic field. (Fig. 3.19)

The variation of Hall voltage with magnetic field is shown in fig. 3.20. The voltmeter which is used to measure V can be directly calibrated in terms of Gauss. The graph can be also used to measure any unknown magnetic fields.

(b) Electronic Multipliers

From Hall effect, we have V_H = R_H B_Z I₁ / t

Since R_H and t are constant for an element

V_H ∝ B_Z I₁

But, the magnetic field B_z is proportional to current (I₂) through the coil.

i.e., B_z ∝ I₂

V_H - I₂  ∝ I₂

i.e., V_H is a measure of the product of two currents. This is the basic principle used in analog electronic multipliers. The fig. 3.21 shows the circuit diagram for electronic multiplier.

(c) Electronic Wattmeter

Hall effect is used to measure electrical power dissipated in a load. The instrument used to measure the power in a circuit using Hall effect principle is known as Hall effect - Watt meter.

S is Hall effect sample. It is placed in a magnetic field B_z produced by the load current I_L passing through the coils CC as shown in fig. 3.22.

The voltage across the load V_L drives the current

I_y = V_L / R through the sample. R is a series resistance which is

>> than the resistance of the sample and that of the load. Also I_y << I_L

If 't thickness of the sample, then the measured Hall voltage

V_H = R_H B_Z I_y / t

V_H  ∝ B_Z L_y (Since R_H and t are constant)s

Since B_Z ∝ I_L and I I_y ∝ V_L

This is the electric power dissipated by the load. The voltmeter that measures V_H can be calibrated to read power directly.

Metal Semiconductor (MS) Contact

Metal-Semiconductor (MS) contact plays a very important role in the present day electronic devices and Integrated Circuit (IC) technology.

When a metal and a semiconductor are brought into contact, there are two types of junctions formed depending on the work functions of the metal and semiconductor.

Types of Metal Semiconductor junction

(i) Schottky junction – ϕ_m > ϕ_semi

(ii) Ohmic junction ϕ_semi < ϕ_semi

ϕ_m - Work function of metal

ϕ_z - Work function of semiconductor

Work Function: Energy required to raise the electrons from the metal or the semiconductor to the vacuum level.