In the energy band
diagram of n-type Si semiconductor, the donor energy level ED is slightly
below the bottom EC of the conduction band and electrons from this level
move into the conduction band with very small supply of energy At room
temperature, most of the donor atoms get ionised but very few (~1012)
atoms of Si get ionised So the conduction band will have most electrons
coming from the donor impurities, as shown in Fig 14