The basics of Solids and Solutions

In order to understand the electrochemistry of semiconductors some
basics notions about solids and solutions are nevessary.

2.1 The basics of Solids and Solutions

Electrochemistry of semiconductors in general and of III-V compounds in particular has a long tradition. One of the most well known electrochemical processes in respect to III-V compounds is the so called Photo-Electrochemical Etching (PEC) [12]. PEC etching is a particular case of Electro-Chemical Etching (ECE), encompassing light-induced electrochemical reactions at semiconductor/electrolyte interfaces.

If the energy of the light used to illuminate the semiconductor/electrolyte interface is higher than the electronic band gap of the semiconductor, then the incident photons will generate electron-hole pairs. The generated holes and electrons stimulate the local, i.e. selective, material etching, or deposition reactions respectively. Selectivity is the major advantage of PEC etching. Therefore, electrochemical etching of semiconductors is mainly used to fabricate anisotropic structures in micro- and optoelectronics. This technique is especially effective with III-Vs compounds, due to their high anisotropy and higher solubility of the reaction products in nearly all kinds of electrolytes.

In a nut shell, electrochemical etching is nothing else but the dissolution of a solid material as a result of charge transfer between a solid and a liquid solution . However, the charge transfer processes are complex and strongly dependent on the distribution of the charge carriers within the solid and solution. Below we will discuss the models used to describe the charge carriers in these two environments.

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