I have developed some creative dramas about this for high school level
students. Some snippets from my workshop are pasted in below.
One of the reasons for this is to dispel a common misconception concerning
insulators, semiconductors, and conductors. It is commonly believed that
electrons move easily in a conductor, move more slowly in a semiconductor,
and move even slower in an insulator. This is not true. In fact, in some
semiconductors, such as GaAs, electrons move more easily (have higher
mobility) than in a metal such as copper. Students should learn that it is
the density of free (mobile) electrons n that differentiate these classes of
materials. In a conductor, n ~ 10^22 cm-3, whereas in a semiconductor,
typical values for n are 10^15 - 10^19 cm-3, and in an insulator, n < 10^10
cm-3.
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Tell the students that they will now perform a more sophisticated creative
drama simulation of a semiconductor and show first how electron flow can
contribute to the electrical conductivity of semiconductors. Next a
simulation of hole conductivity will be performed, where holes, the absence
of electrons, are responsible for the electrical conductivity.
To illustrate electron flow.
· Initially, of the students in row 1, only the student in the middle column
has a ball that can move. (This ball should be different than the balls that
don’t move.)
· This student in row 1 then passes the ball to a student without a ball in
row 2.
· This student in row 2 then passes the ball to a student without a ball in
row 3.
· This student in row 3 then passes the ball to a student without a ball in
row 4.
· This student in row 4 then passes the ball to a student without a ball in
row 5.
As shown in the figure, the position of the free electron (ball) drifts
down the lattice of atoms (students) until it reaches the battery terminal
In a semiconductor that is an electron conductor, there are many bound
electrons, few mobile (free) electrons and many open spaces (available
energy states) to which electrons can move.
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To illustrate hole flow.
· Initially, only one student in row 5 does not have a ball. One student in
row 4 then passes their ball to the student in row 5.
· Now that student in row 4 does not have a ball. A student in row 3 then
passes their ball to that student in row 4.
· Now that student in row 3 does not have a ball. A student in row 2 then
passes their ball to that student in row 3.
· Now that student in row 2 does not have a ball. A student in row 1 then
passes their ball to that student in row 2.
Note that the position of the hole, represented by the student without the
ball, moves in the opposite direction to the ball motion: the electron
(ball) moves in one direction, the hole (student without a ball) moves in
the opposite direction.
In a semiconductor that is a hole conductor, there are only a few spaces
(vacancies) available for electrons to move to. As shown above, the net
effect of the movement of an electron is a net flow of a hole in the
opposite direction.
Dr. Lawrence D. Woolf; General Atomics; 3550 General Atomics Court, San
Diego, CA 92121; Phone:858-455-4475; FAX:858-455-4268; http://www.sci-ed-ga.org