The effect of this doping process on the relative conductivity can best be described through the use of the energy-band diagram of Fig. 1.8 . Note that a discrete energy level (called the donor level) appears in the forbidden band with an E g significantly less than that of the intrinsic material. Those free electrons due to the added impurity sit at this energy level and have less difficulty absorbing a sufficient measure of thermal energy to move into the conduction band at room temperature. The result is that at room temperature, there are a large number of carriers (electrons) in the conduction level, and the conductivity of the material increases significantly. At room temperature in an intrinsic Si material there is about one free electron for every 10 12 atoms. If the dosage level is 1 in 10 million (10 7 ), the ratio 10 12 >10 7 10 5 indicates that the carrier concentration has increased by a ratio of 100,000:1.