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Introduction
 Dielectric or electrical insulating material are understood as the material in which electrostic field can persist for long times. Layers of such substance are commonly inserted into capacitors to improve their perfomance, and the term dielectric refers specifically to this application.879.
An electric field polarizes the molecules of dielectric producing concentrations of charge on its surface that create an electric field opposed (antiparallel) to that of capacitor. This reduces the electric potential. Considered in reverse, this means that, with a dielectric, a given electric potential causes the capacitor to accumulate a larger charge.
Applications Now it is important to recognize
that for the same electric field Ex, the Hall voltage
for p type carriers will have opposite sign from that for
n carriers. (That is, the Hall coefficient R has a different
sign.) Thus, the Hall field Ey will not be able
to compensate for the magnetic force on both types of carriers
and there will be a transverse motion of carriers; however,
the net transverse transfer of charge will remain zero since
there is no current through the 3, 4 contacts; this statement
is expressed as
while
where the mobility is always a positive
number; however, vx+
has the opposite sign from vx-,
but
where
thus
and thus
and for the Hall coefficient RH
.............(5)
Equation 5 correctly reduces to Eq. 1 when
only one type of carrier is present.
Since the mobilities µh
are not constants but functions of T, the Hall coefficient
given by Eq. 5 is also a function of T and it may become zero
and even change sign. In general µe >
µh so that inversion may happen only if p
> n; thus "Hall coefficient
inversion" is characteristic of only "p-type"
semiconductors
At the point of zero Hall Coefficient,
it is possible to determine the ratio of mobilities b=µe/µh
in a simple manner.
(Ref: Experiments in Modern Physics by
A.C. Melissinos)
The Set-up consists of the
following
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- Hall probe (Ge
: p type)
- Oven
- Temperature sensor
- Hall Effect Set-up, DHE-22
- Electromagnet, EMU-50V
- Constant Current Power Supply, DPS-50
- Digital Gaussmeter, DGM-102
Hall Probe (Ge : p-type)
Ge single crystal with four spring type pressure
contact is mounted on a glass-epoxy strips. Four leads are
provided for connections with the probe current and Hall voltage
measuring devices.
Oven
It is a small oven which could be easily mounted over the
crystal or removed if required.
| Technical details |
- Size : 35 x 25 x 5 mm (internal
size)
- Temperature Range : Ambient to
100° C
- Power requirement : 12 W
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Temperature
Sensor
Temperature is measured with Cromel-Alumel thermocouple
with its junction at a distance of 1 mm from the crystal
Hall Effect Set-up,
Model : DHE-22
The set-up, DHE-22 consists of two sub set-ups,
each consisting of further two units.
a) Measurement of Probe Current
& Hall Voltage
This unit consists of a digital millivoltmeter and
constant current power supply. The Hall voltage and probe
current can be read on the same digital panel meter through
a selector switch
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(a) Digital Millivoltmeter
Intersil 3½ digit single chip ICL 7107 have
been used. Since the use of internal reference causes
the degradation in performance due to internal heating
an external reference have been used. Digital voltmeter
is much more convenient to use in Hall Experiment, because
the input voltage of
either polarity can be measured.
Specifications
Range : 0-200mV (100mV minimum)
Accuracy : ±0.1% of reading ±
1 digit
Line regulation : 0.05% for 10% variation |
(b) Constant Current
Power Supply
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.
Specifications
Current : 0-20mA
Resolution : 10mA
Accuracy : ±0.2% of the reading ±1
digit
Load regulated : 0.03% for 0 to full load |
b) Measurement of Thermo
emf and Heater current
The unit consists of a digital
millivoltmeter and constant current power supply. The thermo
emf of thermocouple and heater current can be read on the
same DPM through a selector switch.
| (a) Digital Millivoltmeter
Intersil 3½ digit single chip ICL 7107 have
been used. Since the use of internal reference causes
the degradation in performance due to internal heating
an external reference have been used. Digital Voltmeter
is much more convenient to use,
because the input voltage of either polarity can be
measured.
Specification
Range : 0 - 20 mV
Resolution : 10 mV
equivalent to 0.25ºC in terms of thermo emf
Accuracy : ±0.1% of reading ±
1 digit
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(b) Constant Current
Power Supply
The supply is highly regulated and practical ripple
free source.
Specifications
Current : 0 - 1A
Accuracy : ±0.2% of the reading ±
1 digit
Line regulation : 0.1% for 10% variation
Load regulation : 0.1% for 0 to full load
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