Page 269 - Semiconductor For Micro- and Nanotechnology An Introduction For Engineers

Interacting Subsystems
a junction, where it is usual to define the relative thermoelectric power of
the junction by
(
Π = Π – Π = T ε – ε ) (7.76)
AB B A B A
This effect can be used to pump heat from one region to another, for
example, to cool electronic circuits or even to refrigerate a space.

Bridgeman Heat is absorbed or liberated in a homogeneous conductor when a current
Effect passes across an interface where crystal orientation changes, or when a
current distribution is strongly nonuniform. This effect is sometimes also
called the internal Peltier effect.

Thomson Heat is absorbed or liberated in a homogeneous conductor, subject to a
Effect temperature gradient, that has a current flowing through it. The effect is
primarily caused by the temperature-dependence of the Seebeck coeffi-
cient. In this case, the temperature gradient of the Peltier coefficient
(
⁄
⁄
∂εT) ∂T = ε + T∂ε ∂T leads to an additional term that we denote
the Thomson coefficient after its discoverer
∂ε
τ = T ------- (7.77)
T
∂T
The direction of heat flow is defined by the direction of the current flow
i ; its value is determined by

T 1
j = ∫ τ i T (7.78)
d
T
q
T 0
Other Similar When a thermoelectrically active substance is subject to a penetrating
Effects magnetic induction, a whole range of further “classical” effects are
observed:
• Nernst effect. When heat flows across lines of magnetic force, we
observe a voltage perpendicular to both the heat current and the mag-
netic field.

266 Semiconductors for Micro and Nanosystem Technology