The Hall Effects.ppt.....................

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2. SABOOR JAVED
CLASS : MSPHY-1
st
-1E
2
ROLL NO: S24BPHYS3W02014

3. The Hall Effect

4. Hall Effect
•Discovery
•The physics behind it
•Applications
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5. Discovery
•Observed in 1879
•Edwin Herbert Hall
•E.H. Hall (1855–1938), who discovered it at Johns
Hopkins University in 1879 and then became a
professor at Harvard [from 1881 to 1921].
•Discovered 18 years before the electron
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6. Principles
•Mobile charges pressed to one side from
Lorentz force, immobile charges unaltered
•Creates internal electric potential, known as
Hall voltage.
•For simple metals, is V =
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7. HALL EFFECT.
•The Hall effect isthe deflection of electrons
(holes) in an n-type (p-type) semiconductor
with current flowing perpendicular to a
magnetic field. The deflection of these
charged carriers sets up a voltage, called the
Hall voltage
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8. A Visual Representation
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11. Hall Coefficient
•Magnitude parameter:
•In metals:
•In semiconductors:
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13. Richard Beck -Physics 141A, 2013 13

14. HALL EFFECT MEASUREMENTS
•Hall-effect measurements were performed with a computer-
controlled system, which included a constant current source,
an electrometer, and a high-impedance voltage meter. A
temperature stage equipped with a Joule-Thompson high-
pressure N
2refrigerator was employed to vary the sample
temperature in the range between 80–500 K. Themagnetic
fieldwas 17.4 kG. The samples were configured in a square
Van der Pauw geometry (Van der Pauw, 1958) and typically 5 ×
5 mm
2
. Small-area metal contacts were vacuum evaporated
into the four corners of the samples to obtain ohmic contacts
onn-andp-type GaN for the voltage ranges of interest.
Contacts with good ohmic behavior are preferred for Hall-
effect measurements in order to avoid depletion-layer effects,
which would necessitate film thickness corrections.
Richard Beck -Physics 141A, 2013 14

15. •The Hall-effect measurement yields the sheet
resistance and the Hall coefficient (R
H(n, p)) of
a GaN film. Under the assumptions of both
uniformity of film thickness (d) and the
transport properties within the films, the
resistivity (ρ), the carrier concentration (n,p),
and the carrier Hall mobility (μ
n, μ
p) can be
determined from the measured quantities.
Richard Beck -Physics 141A, 2013 15

16. Applications
•Measurement can tell about charge carrier
mobility, concentration
•Conversely, knowing the above allows for
sensitive measurement of an external B-field
•Resistant to outside contaminants unlike
optical, electromechanical testing
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17. New Discoveries
•QuantumHall Effect
•Spin Hall Effect
•Anomalous Hall Effect
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18. References
•Kittel, Charles, Introduction to Solid State Physics, John Wiley & Sons, Inc.. 2005
•Kasap, Safa. Hall Effect in Semiconductors, University of Saskatchewan, 2001
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19. THANKS! FOR YOUR
ATTENTION
Richard Beck -Physics 141A, 2013 19