Ndopning

N-dopning, or n-type doping, is a process in semiconductor fabrication where donor impurities are introduced into an intrinsic semiconductor to increase the concentration of free electrons. The resulting material has electrons as the majority charge carriers and is used to tailor electrical properties for devices such as diodes and transistors.

The mechanism relies on donor atoms, typically from group V elements in silicon (such as phosphorus, arsenic, or antimony). These dopants have extra valence electrons that can be donated to the conduction band. At room temperature, donors are readily ionized, adding free electrons and shifting the Fermi level toward the conduction band. The electron concentration is set by the dopant density and by compensation from any acceptor impurities.

Dopants can be introduced by diffusion or ion implantation, followed by annealing to repair lattice damage and electrically activate the dopants. The choice of dopant, implantation energy, and annealing conditions determines the dopant profile, which in turn influences device behavior such as junction depths and carrier mobility.

N-doped silicon is used to form pn junctions with p-type regions, enabling diodes and transistors. In metal-oxide-semiconductor devices, n-type regions form n-channel devices (nMOS). Doping profiles affect threshold voltage, resistivity, and breakdown characteristics. High dopant levels can lead to degenerate semiconductors, where conduction is dominated by free electrons. Considerations during processing include dopant diffusion, activation efficiency, and compensation by unintended impurities. Typical dopant densities range from about 10^14 to 10^20 atoms per cubic centimeter, depending on the application.