The anodic oxidation processes is usually carried out at room temperature. Thus, impurity concentrations present in the semiconductor are not altered during this process. As a result, anodic oxidation is a useful means for the controlled removal of layers of silicon and gallium arsenide at room temperature, and is often used as a diagnostic tool. This technique can also be used to grow reasonably high quality oxides on gallium arsenide.
Anodic oxidation or anodization, is carried out by placing the semiconductor in an electrolytic cell, as shown in Fig.3.18, where it is connected to the positive terminal of a power supply so that it serves as the anode. A noble metal such as platinum is connected to the negative terminal of the supply, and serves as a cathode. A large variety of electrolytic formulations can be used. The primary oxidizing component of all of these is water, which dissociates into H + and (OH) - .