Basics of the Semiconductor-Electrolyte Contact

This chapter is dedicated to the basics of the silicon-electrolyte contact, with emphasis on the semiconductor side of the junction. The phenomenology of the I-V curve is discussed, together with basic charge states of semiconductor electrode like accumulation, depletion and inversion. Electrostatic and electrodynamic properties will be described, with emphasis on the direct current (DC) properties of the semiconductor electrode, while alternating current (AC) properties are discussed in Section 10.2. Details of charge exchange and mass transport as well as details of the reactions at the microscopic level are considered in Chapter 4. 

while for an n-type semiconductor the reverse is true. An analog to the SCR in the semiconductor is an extended layer of ions in the bulk of the electrolyte, which is present especially in the case of electrolytes of low concentration (typically below 0.1 rnolh1). This diffuse double layer is described by the Gouy-Chap-man model. The Stern model, a combination of the Helmholtz and the Gouy-Chapman models, was developed in order to find a realistic description of the electrolytic interface layer. 

The current-voltage (I-V) characteristic of a semiconductor-electrolyte contact is determined by both the semiconducting nature of the electrode, as well as by the ionic and molecular species present in the electrolyte. The current density at the electrode for a certain potential is limited by the reaction kinetic at the interface, or by the charge supply from the electrode or the electrolyte. 

A Schottky diode is always operated under depletion conditions flat-band condition would involve giant currents. A Schottky diode, therefore, models the silicon electrolyte interface only accurately as long as the charge transfer is limited by the electrode. If the charge transfer becomes reaction-limited or diffusion-limited, the electrode may as well be under accumulation or inversion. The solid-state equivalent would now be a metal-insulator-semiconductor (MIS) structure. However, the I-V characteristic of a real silicon-electrolyte interface may exhibit features unlike any solid-state device, as 

In the next section the charge states of the electrode and the electrochemical reactions are discussed for acidic, especially fluoride-containing electrolytes followed by a section dealing with alkaline electrolytes. 

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