dependent, currents can flow in the rod in both directions. In the case of θ ¼ 50 K, it
can be seen that the critical voltages for positive or negative V are different.
Therefore, there exists a range of the voltage in which currents can flow in one
direction but not the other. Therefore the local temperature change has the effect of a
switch which is off for low voltages and on for high voltages. This provides a basic
means for thermally manipulating currents in a piezoelectric semiconductor rod.
When θ ¼ 35 K, for specific values of the voltage that are low, critical, or high,
(b) shows the corresponding distributions of the electric potential along the rod.
When V ¼ 0.3 volts, the potential well still exists, blocking possible currents. When
V ¼ 1.5 volts, it has overcome the potential well, and the potential distribution
becomes monotonic. Hence currents can flow freely.
Fig. 7.5 Fields produced
by a local temperature
change predicted by the
linear theory. (a) Potential
barrier and well. (b) Electric
polarization
7.2 Effects of a Local Temperature Change
187