ABSTRACT
The devices for energy production and storage are formed with different types of materials and interfaces. We start our discussion with metals and semiconductors that are at the heart of modern electronic and photovoltaic systems. Some basic properties of the semiconductors are reviewed, and several elements of the energy diagrams are built that will be used to describe and understand the operational function of devices. Electric potential energies are determined by electrostatic conditions that depend on the distribution of electric charges. This method is sufficient to describe energetics of electrons so far as the electrons reside in a material or phase that is chemically homogeneous. But in order to make junctions in working devices we consider different phases, in contact, and the electron in transit across the interface will experience a combination of chemical and electric forces which cannot be simply separated. Therefore, electrostatics is generally limited to describe energetics of electrons, and one must treat the electron system in terms of equilibrium states of thermodynamics. In this context, a number of fundamental concepts such as the Fermi level, the surface dipole, the chemical potential, and the Volta and Galvani potentials will be carefully defined and discussed with examples. These concepts are stated in this chapter in total equilibrium conditions but they form the basis for the description of nonequilibrium phenomena such as the diffusion flux.
