Characterisation of trapped electric charge carriers behaviour at nanometer scale by electrostatic force microscopy

Abstract

Atomic force microscopy (AFM) and related electrical probe techniques such as electrostatic force microscopy (EFM) can be used to perform injection and detection of electric charge carriers in nanostructures or oxide layer at the nanometer scale. In this paper the control and the deposition of both positive and negative local charges are described and discussed. A basic introduction to both the theoretical and experimental techniques of EFM is also presented. In addition a review of the analytical calculation of tip–surface capacitance interaction is described and then utilised to estimate charge storage in oxide layers and nanostructures from EFM images or spectroscopy curves. The charge resolution of EFM at room temperature and a controlled atmosphere is estimated to be about 20 charge carriers. The EFM technique is also used to inject charges and to study their behaviour in confined silicon nanostructures covered by a thin layer of oxide and separated from the Si substrate by a SiO 2 layer. The total injected charge is found to depend on the thickness of the oxide layer. The electric field has emerged to be a key parameter in the injection mechanism. The dynamics and propagation of the deposited charge carriers have been studied and a homogenous distribution of the charge in the nanostructure has been observed. Thanks to these studies and observation, the localisation of the trapped charges has been determined: it occurs mainly in the silicon pattern rather than on the thin covering oxide layer. This charge localisation together with charge energy calculation leads to a better understanding of the origin of the charge dissipation.