{"id":"doping","level":"matter","name":"Donor and acceptor doping","shortName":"Doping","role":"Changes carrier populations by introducing selected impurity atoms.","description":"Doping deliberately changes a semiconductor by incorporating a small population of other elements. In silicon, a donor such as phosphorus can supply an electron; an acceptor such as boron creates a hole in the carrier description. The crystal remains a material with extended electronic states, rather than isolated dopant atoms acting as individual switches. N-type and p-type describe the dominant mobile carrier, not a permanently charged bulk object. Spatially different doping regions help establish junctions and useful terminal behavior. Modern devices may combine heavily doped source/drain regions with lightly doped channels, so a single uniform sprinkling is only a teaching view, not a production doping map.","specs":[{"label":"Donor example","value":"Phosphorus","context":"Group-V atom in a silicon host."},{"label":"Acceptor example","value":"Boron","context":"Group-III atom in a silicon host."},{"label":"Quantity to specify","value":"Concentration and profile","context":"An actual device requires process-specific characterization."}],"interfaces":[{"name":"Host crystal","direction":"in","signal":"Substitutional sites"},{"name":"Carrier distribution","direction":"out","signal":"N-type or p-type regions"}],"tradeoff":"More carriers can reduce resistance. Impurities and statistical variation can also degrade transport and uniformity.","whyAI":"Doping helps make complementary switching networks possible. Those networks become memory, arithmetic, and control circuitry.","related":["crystal-lattice","pn-junction","source-drain"],"sources":[{"title":"MIT 6.777J — Semiconductor Materials","url":"https://ocw.mit.edu/courses/6-777j-design-and-fabrication-of-microelectromechanical-devices-spring-2007/6de08ad7d4ee670c283ce5ec0e6a653b_07lecture07e.pdf"}],"scale":"Atomic substitutions within nanometer-to-micrometer device regions","kind":"dopants","mechanism":["Replace selected silicon host atoms with donor or acceptor species.","Allow these species to change the available mobile electron or hole populations.","Arrange different regions spatially to obtain useful junctions and transistor terminal behavior."],"misconception":"N-type does not mean the bulk material carries an uncompensated permanent negative charge; it identifies the majority mobile carrier.","check":{"question":"What distinguishes n-type silicon?","options":["Its majority mobile carriers are electrons","Every atom is negatively charged","It contains no holes at any temperature"],"answer":0,"explanation":"N-type refers to which mobile carriers dominate. Ionized dopants and the rest of the solid also participate in charge balance."},"branch":"Atomic foundations","subbranch":"Carrier engineering","science":[{"title":"Mass action and donor control","equation":"np = nᵢ²; n ≈ N_D; p ≈ nᵢ² / N_D","explanation":"For donor-dominated silicon, the majority electron density follows the activated donors while the minority hole density decreases. This connects atomic substitution to measurable conductivity.","assumptions":"Thermal equilibrium, full donor ionization, negligible compensation, N_D much larger than nᵢ, and nondegenerate statistics; heavily doped materials require a better model."}],"history":[],"learningObjective":"Use mass action and donor concentration as separate assumptions.","engineeringExample":"If N_D is much larger than n_i, the simple estimate gives n≈N_D and p≈n_i²/N_D; compensation and incomplete ionization can change both.","evidenceNotes":"The displayed relation is a nondegenerate, charge-neutrality approximation.","visualFamily":"device-crosssection","prerequisites":["energy-bands"],"labId":"library","scope":"Use the switching investigation to connect physical charge, circuit load and arithmetic; the numerical library has no standalone model of this lesson’s full mechanism.","investigationId":"switching","labScope":"Use the switching investigation to connect physical charge, circuit load and arithmetic; the numerical library has no standalone model of this lesson’s full mechanism."}