Effect of pressure on variable range hopping in amorphous semiconductors

The electric conductivity and thermo-electric power were measured under pressure up to 10 GPa and in the temperature range from 100 K to 300 K in evaporated amorphous Ge. The temperature dependence of conductivity is found to be well described by sigma = sigma(0)(T/T-0)(n) with 6 less than or equal to n less than or equal to 7 in the pressure rang to 6 GPa. The value of n varies with increasing pressure. The pressure coefficient, dln n/dP, is about 3.0 X 10(-2) GPa(-1) below; 1.6 GPa and -3.3 X 10(-2) GPa(-1) above 1.6 GPa. The thermopower at room temperature decreases with increasing pressure, Results are discussed from several hopping conduction models.