Explain why carrier mobility in group 2 and 4 is lower than the group 3 and 5
Carrier mobility is a measure of how easily charge carriers (such as electrons or holes) can move through a material under the influence of an electric field. Generally, materials with higher carrier mobility exhibit better conductivity.
In group 2 and 4 elements, such as beryllium (Be), magnesium (Mg), carbon (C), and silicon (Si), the carrier mobility is lower compared to group 3 and 5 elements, such as boron (B), aluminum (Al), phosphorus (P), and arsenic (As). There are a few reasons for this difference in carrier mobility.
1. Crystal Structure: Group 2 and 4 elements tend to have a more closely packed crystal structure compared to group 3 and 5 elements. This results in a higher degree of bonding and stronger forces between atoms in the lattice. These strong forces impede the movement of charge carriers, making it more difficult for them to move through the material.
2. Electron Configuration: Group 2 and 4 elements have a filled valence shell, which means they have a lower number of free electrons available for conduction. In contrast, group 3 and 5 elements have either one or three extra electrons in their valence shell, respectively, which makes it easier for these electrons to move and contribute to conductivity.
3. Band Structure: The electronic band structure of materials also affects carrier mobility. In group 2 and 4 elements, the energy bands for electrons and holes are usually narrower, resulting in a lower mobility. In group 3 and 5 elements, the wider energy bands allow for greater electronic movement, resulting in a higher carrier mobility.
In summary, the lower carrier mobility in group 2 and 4 elements can be attributed to their crystal structure, electron configuration, and band structure, which hinder the movement of charge carriers. Group 3 and 5 elements, on the other hand, have a more favorable configuration for electron movement, resulting in higher carrier mobility.