ABSTRACT
The potential barrier at the semiconductor surface in contact with a metal or an electrolyte is a determining factor in solid-state device physics and in photoelectrochemistry. Since the height of the barrier can be modified by the applied voltage, the flow of electrons is enhanced in forward mode and impeded in reverse. Therefore, this provides a useful selective contact that is a key component of many electronic and optoelectronic devices. In the first section of this chapter, we treat quantitatively the shape of the barrier at the semiconductor surface in contact with metal (or any solid contact). We stress the importance of the capacitance measurements that reveal different properties of the semiconductor and the barrier. The next section of the chapter provides a detailed view of the properties of semiconductor/electrolyte junctions that are used in photoelectrochemical cells. A general energy diagram is presented to combine the interpretation of the electrochemical measurement with the changes of the local vacuum level. Then, we analyze generic properties of various specific semiconductor junctions, as the p-n junction and the heterojunction. Finally, we discuss small-size nanostructures, such as nanoparticles and nanowires, first considering the depletion layer at the internal surface, and then the nanostructures that operate by homogeneous displacement of the Fermi level.
