Determination of charge density and location of the charge centroid in electrets with semiconducting substrates

A novel method for determining the amount and the mean spatial depth of charges in electret-semiconductor systems is presented. It consists of two nondestructive measurements, from which the internal and external electric fields can be calculated independently. First, the surface potential at the electret-air interface is measured by an electrostatic voltmeter. Secondly, using a contacting front electrode, a metal insulator semiconductor structure is formed, on which capacitance or conductance voltage measurements are carried out. With these, one obtains the surface potential at the electret-semiconductor interface. The charge centroid and the charge density can now be calculated. Application of the method to 1-μm SiO₂ electrets on silicon substrates showed that the charge centroid and the charge density could be varied with an annealing procedure before charging