Contact free potential mapping by vibrating capacitor
The contact free vibrating capacitor method is a valuable tool for investigating the surface potentials of solid surfaces. The purpose of the present article is to summarize the theory and capabilities of the vibrating capacitor method, especially scanning vibrating capacitor pictures in the electronics. After a brief review some results will be discussed, such as a contact potential map taken from a printed circuit board, a surface potential map from a biased ceramic thick film circuit and some results from silicon solid state devices and solar cells. Potential maps contain a lot of information concerning the surface conditions, included the inhomogeneities of the technology, bias and other additional excitation. These potential maps may help in the development, quality control and defect analysis
Surface photovoltage phenomena: theory, experiment, and applications
The theoretical concepts, experimental tools, and applications of surface photovoltage (SPV) techniques are reviewed in detail. The theoretical discussion is divided into two sections. The first reviews the electrical properties of semiconductor surfaces and the second discusses SPV phenomena. Next, the most common tools for SPV measurements and their relative advantages and disadvantages are reviewed. These include the Kelvin probe and the use of MIS structures, as well as other less used techniques. Recent novel high-spatial-resolution SPV measurement techniques are also presented. Applications include surface photovoltage spectroscopy (SPS) which is a very effective tool for gap state spectroscopy. An in-depth review of quantitative analyses, which permit the extraction of various important surface and bulk parameters, follows. These analyses include: carrier diffusion length; surface band bending, charge, and dipole; surface and bulk recombination rates; surface state distribution and properties; distinction between surface and bulk states; spectroscopy of thin films, heterostructures and quantum structures; and construction of band diagrams. Finally, concluding remarks are given.
The influence of interfaces and interlayers on the gas sensitivity in work function type sensors
Abstract It is known that barium carbonate can act as CO2 sensitive material in work function type gas sensors in ambient condition. The reaction is due to the formation of bicarbonate species at the surface. The cross-sensitivity to other acidic gases as NO2 was up to now regarded and described in terms of similar reactions on the carbonate surface. In this work it was found that the NO2 sensitivity is due to reactions on the back metalisation of the carbonate film. Using different layer systems different sensitivities can therefore be switched on and off according to the needs in special applications. The design of specialised sensor systems is possible on the base of the results found in this work.