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JamesJames
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Two students performing a Hall voltage measurement using germanium as a semiconductor reversed the magnetic field while holding the bias
current constant but did not get opposite signs for the Hall voltage. The magnitude of Hall voltage detected using a voltmeter was the same as it must be. Based on the sign observed, they could determine the doping of the semiconductor from the a) Lorentz force law and b) direction of the current which they controlled through the bias current. Appropriate procedures were followed and several attempts were made after reconstructing the circuit to rectify the signs. The experiment was attempting to illustrate the basic properties of semiconductivity. This part of the experiment attempted to calculate the Hall coefficient, type of doping (n or p) and the carrier mobility.
Part of experimental science is dealing with equipment breakdown and other
non-idealities. When this happens they had to think carefully about the extent to which their results are affected, and what they could conclude about the physics they were investigating.
Their numerical values for the Hall coefficient and carrier mobility were very close to the literature ones.
What are they able to conclude about the bandgap theory of conductors from their experiment? More specifically, were they able to say whether the samples tested are n-type or p-type semiconductors, or if they're semiconductors at all? Are their Hall voltage measurements discredited (and
why)?
Here' s what I think: The Hall voltage calculations should be valid. The agreement with literature values shows this BUT they cannot say anything about the bandgap theory..i.e. they are unable to determine whether the two samples of germanium are of different doping. They are unable, as a result, to determine whether the samples are infact semi conductors. The sign part could be due to equipmental problems but they reconstructed the circuit so I would say that this is not the problem.
Am I correct? Where and how am I messing up the interpretation of this experimental problem? With the exception of instrumental problems, what could be responsible for this sign changing flaw?
James
current constant but did not get opposite signs for the Hall voltage. The magnitude of Hall voltage detected using a voltmeter was the same as it must be. Based on the sign observed, they could determine the doping of the semiconductor from the a) Lorentz force law and b) direction of the current which they controlled through the bias current. Appropriate procedures were followed and several attempts were made after reconstructing the circuit to rectify the signs. The experiment was attempting to illustrate the basic properties of semiconductivity. This part of the experiment attempted to calculate the Hall coefficient, type of doping (n or p) and the carrier mobility.
Part of experimental science is dealing with equipment breakdown and other
non-idealities. When this happens they had to think carefully about the extent to which their results are affected, and what they could conclude about the physics they were investigating.
Their numerical values for the Hall coefficient and carrier mobility were very close to the literature ones.
What are they able to conclude about the bandgap theory of conductors from their experiment? More specifically, were they able to say whether the samples tested are n-type or p-type semiconductors, or if they're semiconductors at all? Are their Hall voltage measurements discredited (and
why)?
Here' s what I think: The Hall voltage calculations should be valid. The agreement with literature values shows this BUT they cannot say anything about the bandgap theory..i.e. they are unable to determine whether the two samples of germanium are of different doping. They are unable, as a result, to determine whether the samples are infact semi conductors. The sign part could be due to equipmental problems but they reconstructed the circuit so I would say that this is not the problem.
Am I correct? Where and how am I messing up the interpretation of this experimental problem? With the exception of instrumental problems, what could be responsible for this sign changing flaw?
James