The resistivity measurements of semiconductors
can not reveal whether one or two types of carriers are present;
nor distinguish between them. However, this information can
be obtained from Hall Coefficient measurements, which are
also basic tools for the determination of carrier density
and mobilities in conjuction with resistivity measurement.
As you are undoubtedly aware, a static magnetic field has
no effect on charges unless they are in motion. When the charges
flow, a magnetic field directed perpendicular to the direction
of flow produces a mutually perpendicular force on the charges.
When this happens, electrons and holes will be separated by
opposite forces. They will in turn produce an electric field
which depends on the cross product of the magnetic intensity,
, and the
current density, J.
= R x
Where R is called the Hall coefficient.
Now, let us consider a bar of semiconductor,
having dimension, x, y and z. Let
is directed along X and
along Z then h
will be along Y, as in Fig. 2.
Then we could write
Where Vh is the Hall voltage appearing between
the two surfaces perpendicular to y and I = yz
Hall Effect experiment consists
of the following:
1. (a) Hall
Probe (Ge Crystal); (b) Hall
2. Hall Effect Set-up
3. Electromagnet, EMU-75
4. Constant Current
Power Supply, DPS-175 or DPS-50
5. Digital Gaussmeter,
Hall Probe (Ge Crystal)
single crystal with four spring-type pressure contacts
is mounted on a sunmica-decorated bakelite strip. Four
leads are provided for connections with measuring devices.
Ge single crystal n or p-type as desire
Spring type (solid silver)
potential: <1mV (adjustable)
is designed to give a clear idea to the students about
Hall Probe and is recommended for class room experiment.
A minor drawback of this probe is that it may require
Arsenide crystal with 4 soldered contacts is mounted
on a PCB strip and covered with a protective layer.
The Hall Element is mounted in a pen-type case and a
4-core cable is provided for connections with the measuring
device and current source.
Control Current: 4mA
Field Potential: <4mV
(0-20KG): ±0.5% or better
crystal alongwith its four contacts is visible through
the protective layer. This is mainly used as a transducer
for the measurement of magnetic field.
Hall Effect Setup
DHE-21 is a high performance instrument
of outstanding flexibility. The set-up consists of a digital
millivoltmeter and a constant current power supply. The Hall
voltage and probe current can be read on the same digital
panel meter through a selector switch.
Current Power Supply
Intersil 3½ digit single chip A/D Converter ICL 7107
have been used. It has high accuracy like, auto zero
to less than 10µV, zero drift of less than 1µV/°C, input
bias current of 10pA max. and roll over error of less
than one count. Since the use of internal reference
causes the degradation in performance due to internal
heating, an external reference has been used. Digital
voltmeter is much more convenient to use in Hall experiment,
because the input voltage of either polarity can be
Range: 0-200mV (100mV minimum)
Accuracy: ±0.1% of reading ±1 digit
This power supply, specially designed for Hall Probe,
provides 100% protection against crystal burn-out due
to excessive current. The supply is a highly regulated
and practically ripple free dc source.
Accuracy: ±0.2% of the reading ±1 digit
Load regulation: 0.03% for 0 to full load
Line regulation: 0.05% for 10% variation