Deliberately controlled impurities
Device fabrication removes unwanted contamination while deliberately adding selected impurities. Doping changes carrier populations and creates regions with different concentrations and depths. An impurity is therefore not automatically a manufacturing defect: its electrical role depends on controlled identity, quantity and position within the material.
Donors and n-type material
In silicon, suitable substitutional impurities act as donors, supplying electrons that can enter conducting states relatively easily. Electrons become the majority carriers in n-type material. The label does not mean that the bulk must carry a net negative charge: mobile and lattice charges must both be counted.
References: [1]
Acceptors and p-type material
Acceptor impurities can take electrons from the valence band, leaving mobile holes. Holes dominate conduction in p-type material but are not free positrons. Both carrier types can be present in either material; the names identify which population is the majority under the conditions being considered.
References: [1]
From dopant profiles to devices
Diffusion methods improved control of dopant amount and penetration depth. Combining differently doped regions creates p–n junctions for diodes, transistors and solar cells. Device behaviour also depends on geometry, contacts and processing, so the presence of a dopant alone does not determine a component’s function.