THE HALL EFFECT As Presented by Kishore Padmaraju In Experimental Conjunction with Greg Smith Alex...
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Transcript of THE HALL EFFECT As Presented by Kishore Padmaraju In Experimental Conjunction with Greg Smith Alex...
![Page 1: THE HALL EFFECT As Presented by Kishore Padmaraju In Experimental Conjunction with Greg Smith Alex Pawlicki.](https://reader035.fdocuments.in/reader035/viewer/2022062500/56649d955503460f94a7d50f/html5/thumbnails/1.jpg)
THE HALL EFFECTAs Presented by Kishore Padmaraju
In Experimental Conjunction with Greg Smith
Alex Pawlicki
![Page 2: THE HALL EFFECT As Presented by Kishore Padmaraju In Experimental Conjunction with Greg Smith Alex Pawlicki.](https://reader035.fdocuments.in/reader035/viewer/2022062500/56649d955503460f94a7d50f/html5/thumbnails/2.jpg)
OUTLINE
What Is The Hall Effect?• How does it affect you? • Scientific Principles• Applications
Previous Setup• Shortcomings
New Setup• How it works• Possible Improvements
ResultsConclusion
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HALL EFFECT: THE DISCOVERY
Discovered by Edwin Hall in 1879.
Quantum Hall Effect discovered in 1975
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THE HALL EFFECT
Lorentz Force:F = q[E + (v x B)]
• Hall voltage is produced by charge accumulation on sidewalls• Charge accumulation balances Lorentz Force• Charge accumulation increases resistance
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THE HALL EFFECT: SEMICONDUCTORS
Why Semiconductors?• Ideal number of charge carriers• Charge carriers increase with temperature
What we can learn• Sign of charge carrier• Charge carrier density• Charge carrier mobility• Energy gap
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HALL VOLTAGE
€
VH =−IB
ned= RH
IB
d
For simple conductors
Where n = carrier density, d = conductor length• RH is known as the Hall coefficient
• VH α B Useful for measuring B-Fields
Gaussmeter Probe uses a hall sensor
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HALL COEFFICIENTSemiconductors have two charge carriers
However, for large magnetic fields
Enables us to determine the carrier density
€
RH=−nμ e
2 + pμh2
e(nμ e2 + pμh
2)2
€
RH =1
(p − n)e
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EXPERIMENTAL SETUPLiquid N2 & Heaters are used for temperature control
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NEW EXPERIMENTAL SETUPMotivationOld automated system inadequate
• Previous groups frustrated with results
GoalCreate new DAQ+LabVIEW system
• More reliable measurements• Easy user interface• Easy data collection
Measure • Hall Voltage• Current through Semiconductor• Temperature• Magnetic Field
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MEASUREMENT OF HALL VOLTAGE
Our hall generator is a fully integrated device
• Easy measurement of Hall Voltage• Indirect but easy measurement of current
Semiconductor
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TEMPERATURE MEASUREMENT
Constantan-Copper Thermocouple• Seebeck effect converts temperature gradient to voltage• Non-Linear• Original thermocouple didn’t work!
Where is it?It is this junction between metals!
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MAGNETIC FIELD MEASUREMENT
R
Magnet
Disaster!
4R
V
Vmeasure
BurnedResistor
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DAQ, LABVIEW INTERFACINGDAQ
LabVIEW backend
LabVIEW frontend
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NEW EXPERIMENTAL SETUP
Success• Integrated DAQ w/ Labview• Automated measurements of temperature, hall voltage,
semiconductor current
Setup Shortcomings• Not able to measure magnetic field• Accuracy of hall voltage and temperature measurements• Heaters are too small• Unshielded magnetic field
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RESULTS
n = 1.38E12 cm-3
nSi = 1.5E10 cm-3
€
VH =−IB
ned= RH
IB
d
€
RH =1
(p − n)e≈1
−ne
(-) slope (-) charge carriers
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RESULTS
Increase Temperature Increased ResistanceVH α T-3/2
These results are displeasing
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RESULTSPrior results when experiment was conducted manually
Note: sign was flipped on purpose
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CONCLUSIONS
What we learned about• The Hall Effect• Labview/DAQ integration• Common problems in experimental setup• Safety (Liquid N2)• Maintaining team motivation
Who we learned from• Steve Bloch• Professor Howell