Impedance spectroscopy of Si whiskers in the range of metal-insulator transition
Introduction. The paper deals with investigation of impedance spectroscopy of Si whiskers with doping concentration in the vicinity to metal-insulator transition in the region of low (4,2 - 70 K) temperature and frequency range 0,01 - 250x103 Hz. Experimental results. The silicon whiskers were grown by chemical vapour deposition method in closed bromine system. The whiskers of 40x10-6 m in diameter have boron concentration from 2×1018 to 2×1019 сm-3. The impedance spectroscopy of Si whiskers was investigated with use of Lock-in amplifier in the region of low (4,2 - 70 K) temperature and frequency range 0,01 - 250 x 103 Hz. The investigations showed that in the range of zone conductance (T= 30 - 70 K) the whisker impedance has inductive character, while at the range of impurity conductance (T = 4,2 - 20 K) impedance changes to capacity character. The reduction of impurity concentration at dielectric side of metal-insulator transition leads to decrease of the whisker capacity in the range of low temperatures. Discussion. An inductive character of whisker impedance is explained skin-effect of conductance in thin whisker, while capacity character of the whisker impedance is connected with hopping conductance on impurity band. Conclusions. Character of changes of Si whisker impedance conductance is discussed in the frame of hopping conductance on impurity band, which takes place at low temperatures.