Types of semiconductors.

1) n-type semiconductors

semiconductors are formed elements from Vth group ¢ As and Sb. Addition of a percent of such elements may increase the conductivity by several powers of ten. Ag the impurity increases the ionization  energy decreases.

(2) p-type semiconductor p-type

semiconductors are formed by doping with element from the third group, ie. B, Al, Ba, In. At absolute  zero, the holes remains bound to the impurities, but as the temperature is increased, valence electrons may  be excited into the bound holes with the result that holes are created in the valence band.  At low temperature conductivity results  predominantly from holes produced by excitation  of valence  electrons into acceptor levels.