Thermoelectric Power of Germanium below Room Temperature

The thermoelectric power of germanium single crystals has been measured in the temperature range 10 to 300°K. $N$-type samples of various impurity content have been investigated. Results show that the thermoelectric power $Q$ decreases with increasing concentration of carriers. A few values of the heat conductivity are also reported.

The conventional theory predicts a relation between the thermal emf and the Hall coefficient. The temperature dependence of the thermoelectric power is in good agreement with this relation at temperatures higher than 200°K. Below this temperature $Q$ rises sharply above the value given by this expression, reaches a maximum of several millivolts per degree near 15°K and decreases again at lower temperatures.

Large deviations may be expected at low temperatures due to the disturbance of the phonon equilibrium. The phonon current has a strong influence on the interaction with electrons and may lead to a maximum in the thermoelectric power at low temperatures. The contribution due to the non-equilibrium of the lattice is proportional to the ratio of phonon and electron mean free path. The former is related to the thermal conductivity while the latter can be derived from electrical data.