Semiconductors Properties and Characterization Term

Electrical conductivity of a myriad of elements and compounds gracing the earth’s surface can be classified depending on the electron energies in both the valence and the conduction bands¹. Ideally, the lower energy bands which are normally filled up are always irrelevant when it comes to electric conductivity. With this in mind, these materials can be classified as insulators, conductors and semiconductors. In a synopsis, insulators are poor conductors which have no mobile electrons under normal conditions. Moreover, they lack electrons in their conduction band despite having a filled up valence band. Importantly, the gap separating the conduction and the valence bands is very wide. As such, electrons face an uphill task to cross over to the conduction band. For conductors; however, there exist numerous mobile electrons in the conduction band which are made available owing to the fact that both the valence and the conduction bands overlap. For these materials, no gap exists between the two bands. When we focus on the semiconductors, as the name suggests, these materials have conductive abilities that lie amid insulators and conductors. Examples of these materials include silicon and germanium; all group four elements. For these types of materials, the gap separating both the conduction and the valence bands is very thin. This gap can be overcome by an energy equivalent to 1ev. Importantly, the conduction band is near-empty while the valence band is near-full at 0⁰ K. When the temperature increases, electrons shift from the valence band to the conduction band to enhance conductivity. It is worth noting that as the electrons shift they create positive holes in the previous band while at the same time add extra electrons in the conduction band. As such, current in semi conductors is the total sum of both the electrons and the positive holes which move in the opposite directions. Figure 1 below shows the aforementioned types of materials.