Quantitative Analysis of Kelvin Probe Force Microscopy on Semiconductors

Abstract

As is well known, Kelvin Probe Force Microscopy (KPFM) is a powerful and versatile tool to measure the contact potential difference (CPD) in metals. Here, we discuss the application of KPFM for the investigation of semiconducting materials, where the interpretation of KPFM is complicated by band bending and surface charge. Nevertheless, it is demonstrated that the signal measured with KPFM in semiconductors should be interpreted as the contact potential difference (CPD). This interpretation enables the extraction of information related to semiconductor properties such as the dopant density, surface charge, density of surface states, and band bending. The CPD description and its validation are discussed in detail. Also, model calculations of the expected KPFM signal are presented for a wide range of doping concentrations and for various types of surface charge models, including surface states with a Fermi level dependent charge and surface states with fixed charge. It is demonstrated that the model calculations within the CPD model are consistent with experiments from the literature. As an example of how KPFM data on semiconductors can be analyzed, it is shown how information on surface charge is obtained from measurements on Si pn-junction dopant profiles. Combining KPFM with illumination provides many interesting possibilities for the study of semiconductors, which are briefly discussed at the end of this chapter.