The concentration of electrons and holes in a semiconductor is kept at a certain constant when they are in thermal equilibrium; but this is a dynamic equilibrium, where they recombine and are produced at the same time, and they remain at a certain value at a certain temperature.

 

For example, in the case of n-type semiconductors, in the case of thermal equilibrium, if the concentration of electrons is further increased by doping with donors, the probability of electrons and holes recombination will increase accordingly, which will lead to the concentration of minority carriers—holes. Significantly lower. Therefore, the higher the doping concentration of the semiconductor, the greater the majority carrier concentration, and the smaller the minority carrier concentration. There is a certain relationship between the semiconductor thermal equilibrium carrier concentration-thermal equilibrium condition: nopo=ni2. In the case of full ionization of impurities, the majority carrier concentration no≈ND (doping concentration), then the minority carrier concentration po=ni2/no≈ni2/ND.