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Research Facility
Hall measurement system 
Function:
The Hall measurement system is capable of measuring resistivity, carrier
concentration and mobility of semiconductors over a wide range of
temperatures and magnetic field strengths. Studies of Hall coefficient
versus temperature and magnetic field yield a wealth of information
about the semiconductor sample:
- Carrier freeze out
- Two-dimensional electron gas (very useful for the characterization of
various interfaces)
- Crossovers in conductivity
Accurate values of carrier concentration and mobility of each
Molecular Beam Epitaxy
grown layer is measured using this system and hence provides the
vital feedback loop to standardize the growth conditions of MBE
layers for various different applications such as:
- Medium wavelength infrared (MWIR)
- Long wavelength infrared (LWIR)
- Multi-color detector arrays
Fundamental information, such as the activation energy of dopants,
is also obtained using these measurements.
Specifications:
The Hall measurement system is capable of measuring over a wide range
of conditions:
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Temperature:
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300 K to 4 K
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Magnetic field strength:
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0 to 1.5 Tesla
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Three samples can be measured simultaneously in Van der Pauw geometry
and the measurement is completely automated. The low temperature is
achieved by a closed-cycle helium system (CF200, from Oxford
Instruments). The voltages are accurately measured using
Keithley
products: a Model 220 programmable current source and a Model 195
voltmeter. A Model 706 scanner from Keithley, along with two Model
7056 general purpose scanner cards per sample, are used to eliminate
any unwanted voltages arising due to misalignment of contacts and
sample inhomogeneity.
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