Donoratoms

Donor atoms are impurities intentionally introduced into a semiconductor material to increase the number of free charge carriers, specifically electrons. This process is known as doping. In intrinsic, pure semiconductors like silicon or germanium, the number of free electrons and holes is limited by the material's band gap and temperature. By adding donor atoms, which have more valence electrons than the semiconductor atoms they replace, an excess of electrons is created. These extra electrons are loosely bound to the donor atom and can be easily excited into the conduction band, contributing to electrical conductivity.

The donor atom itself becomes a positively charged ion once it has donated an electron, but it is fixed within the crystal lattice and does not contribute to current flow. Common donor atoms for silicon and germanium are elements from Group V of the periodic table, such as phosphorus, arsenic, and antimony. These elements have five valence electrons, while silicon and germanium have four. When a Group V atom replaces a Group IV atom in the crystal lattice, four of its valence electrons form covalent bonds with neighboring semiconductor atoms. The fifth valence electron is then relatively free to move.

The presence of these excess electrons makes the semiconductor n-type, as the majority charge carriers are negative. The concentration of donor atoms directly influences the conductivity of the n-type semiconductor. Higher doping concentrations lead to a greater number of free electrons and thus higher conductivity. Donor atoms play a crucial role in the fabrication of semiconductor devices like diodes and transistors.