= Solution
\b[n-type doping] adds donor impurities with weakly bound <electrons> near the conduction-band edge; ionization supplies conduction <electrons> and leaves positive donor ions. \b[p-type doping] introduces acceptors near the valence-band edge, producing <holes> and negatively charged ionized acceptors. Silicon and germanium commonly use group-V donors and group-III acceptors; dopant behaviour in a compound <semiconductor> depends on its lattice site.
Doping sets carrier concentration, <Fermi level> and resistivity. Spatially patterned donor and acceptor regions form <p-n junctions>, transistor source/drain regions and electrical contacts; remote doping can supply carriers to a cleaner conducting layer. Compensation and incomplete ionization mean <carrier density> need not equal the total impurity concentration.
Back to article page
