THERMO-EMF IN Si-Ge SOLID SOLUTION WHISKERS

An influence of strain on the character of temperature dependences for thermo-e.m.f. in p-type Si1-xGex (x = 0.01 / 0.05) solid solution whiskers with boron-impurity concentration closed to metal-insulator transition (MIT) in the temperature range of 4.2/200 K has been investigated. The behaviour of Seebeck coefficient at low temperature range is shown to change substantially under strain. In unstrained samples at temperature decrease Seebeck coefficient is down, while under strain it rises reaching maximum at certain temperatures and then it drops again. The magnitude and temperature position of Seebeck coefficient maximum depend on strain and doping levels. At the approach to MIT from dielectric side and at strain increasing the value of piezo-Seebeck coefficient rises (up to 20 mV/K), while the position of maximum shifts to a low temperature range (from 30 to 4.2 K). Besides, the influence of high magnetic fields (up to 14 T) on the behaviour of piezo-thermo-e.m.f. at 4.2 K has been studied. A quadratic dependence of piezo-Seebeck coefficient on the magnetic field was observed.