Carrier Actions

Several factors affect the mobility of a carrier. The most significant is scattering, the motion-impending collisions within the crystal. These collisions can be an electron bumping into another electron, or a hole or ionized impurities. Scattering may increase/decrease due to temperature and/or the addition of acceptors or donors. The higher the temperature the more excited the carriers are, so the more scattering there will be.

The same occurs with dopants, because not only will there be more carriers to bump into and scatter, dopants will generate ionized impurities which also carry a charge. When the doping concentration is low, the mobilities are pretty much independent of the doping concentration. The mobility of the carriers begins to monotonically decrease as the concentration of the dopants increases.