Applying Ohm's Law to Semiconductors
Classroom Notes
Lesson Study Topics:
- current, voltage, and resistance
- Ohm's Law
- semiconductor devices
- graphical analysis
Notes on Classroom Management:
As this is an "inquiry-based" activity, it is important that students be allowed
to explore this activity without an overabundance of initial instructions.
If there are 1 or 2 students at a terminal working on this, the teacher ought
to be able to circulate among the students, helping them when they need it
and asking leading questions to get them to explore further. The teacher may
find more than one good interpretation of the data: this is to be encouraged
and explored in class discussion. Why students have different interpretations
can lead to an exploration of the basic physics.
Notes on Questions:
- Do silicon semiconductors obey Ohm's Law in general? Do they sometimes
obey Ohm's Law? Exactly? Approximately?
Students should compare the curves they see in the graph
to the expected straight-line relationship that obtains when Ohm's Law holds.
They will also have to decide whether to include or discount the "tail" in all
the curves (exept the no radiation line) at low voltage and current.
- How does neutron radiation affect the resistance of a silicon strip?
One can approximate each curve close enough to a straight
line to take an "average" slope and get the resistance as R = dV/dI = 1/slope.
- Can you construct a graph and/or an equation to show the resistance R of
a silicon strip as a function of the number of neutrons N incident upon that
strip?
Students should make a graph then attempt to find a good
mathematical fit. This might best be done using MS Excel, another spreadsheet,
or a graphing calculator.
- Why do you think neutron radiation affects the resistance of a silicon strip? How could your hypothesis be tested?
This can be a good launch point to discuss nuclear
and particle physics, if desired.