Transient current in nematic cells containing a silicon substrate

Transient currents induced by step voltage or polarity reversal of voltage applied to a liquid crystal cell containing a silicon substrate have been investigated. It is shown that the curves of transient current reveal a minimum for negative polarity of dc voltage relative to a silicon substrate of p-type conductivity. The time of the occurrence of the minimum corresponds to the collection of positive ions from the bulk of the liquid crystal at the silicon surface as a result of drift. This is explained by the formation of a highly resistive layer in the silicon under an electric field of positive ions collected at the silicon surface (a field effect). In polarity reversal experiments, a knowledge of the time of the occurrence of the minimum enables us to estimate the mobility of positive ions, which gives a value of 1.4 x 10-11 M2 Bc-1