THERMOPOWER OF NEUTRON TRANSMUTATION-DOPED GE-GA IN THE HOPPING REGION

The low temperature thermopower of moderately compensated semiconducto r neutron transmutation-doped p-Ge:Ga had been under investigation in tile range 50 to 1.4K. For the valence band conduction (T greater than or equal to 10 K) it shows the important role of the phonon drag effe ct, which is suppressed for the hopping transport via Ga impurity band (T less than or equal to 10 K). It has been shown that there is an ad ditional carrier transport channel contributing to the thermopower in the transition range. At temperatures below 2 K where variable range h opping takes place the thermopower vanishes. Two alternative explanati on of this effect are discussed.