The electric and electronic properties of insulators are difficult to measure by conventional methods which apply metal contacts to the insulator surfaces. A new technique has shown great potential. It enables determination of contact-free, previously unmeasurable fundamental properties of materials, especially of materials with very low charge carrier concentrations and of semiconductors. The technique consists of measuring the dielectric polarization in an electric field gradient. By deconvoluting the various components of the dielectric polarization, bulk and surface contributions can be separated. Thus, unique information is obtained about surface charges, their sign and density as well as their associated internal field. The method is also highly sensitive to changes in the bulk polarization such as may be caused by the dissociation of defects and generation of mobile charges. By applying a static electric field gradient and measuring the response as a function of time, processes with long relaxation times, of the order of seconds to hours, can be evaluated. Such processes may be due to charge carriers with very low drift mobilities which, however, may play an important part in determining the long-term stability of electronic devices or ferroelectrics. The objective of the research is to develop a Charge Distribution Probe which allows one to perform measurements with high spatial resolution and determine the electronic properties of thin insulator layers.
