Resistivity Decrease Due to Donor Spin Resonance in n-Type Germanium

A decrease in the resistivity associated with donor spin resonance has been observed in the liquid helium temperature range in arsenic- and phosphorus-doped germanium, whose donor concentrations belong to the intermediate concentration region of impurity conduction phenomenon. The relative changes of the resistivity due to the donor spin resonance have been measured as a function of static electric field applied to samples, temperature, microwave power, and donor concentration. The experimental results are explained on the basis of the spin energy transfer model in which the existence of the two different electronic systems, that is, the donor spin system being responsible for the donor spin resonance and the mobile electron system contributing to the charge transport of the intermediate concentration region at low temperatures is assumed, and the microwave energy absorbed by the donor spin system is transferred to the mobile electron system through their mutual exchange interaction and it turns out to increase in the kinetic energy of the mobile electrons and, accordingly, to an increase in their mobilities.