Definitions Glossary — Semiconductors & Electronic Devices — Notes

Term	Definition
Valence band	The highest occupied energy band in a solid at 0 K, formed by valence electrons of the constituent atoms
Conduction band	The lowest unoccupied energy band; electrons in this band are free to conduct electricity
Energy gap / Band gap (E_g)	The forbidden energy range between the top of the valence band and the bottom of the conduction band; no allowed electron states exist here
Intrinsic semiconductor	A pure semiconductor (Si or Ge) with no intentional impurities; n_e = n_h = n_i at thermal equilibrium
Extrinsic semiconductor	A semiconductor deliberately doped with impurity atoms to increase conductivity; either n-type or p-type
Doping	Process of adding controlled amounts of impurity atoms to a pure semiconductor to increase its conductivity
n-type semiconductor	Semiconductor doped with pentavalent (group 15) atoms; majority carriers are electrons; material is electrically neutral
p-type semiconductor	Semiconductor doped with trivalent (group 13) atoms; majority carriers are holes; material is electrically neutral
Hole	A vacancy in the valence band left by an electron; behaves as a positive charge carrier with charge +e
Intrinsic carrier concentration (n_i)	The number of thermally generated electron-hole pairs per unit volume in a pure semiconductor at a given temperature
Mass action law	n_e × n_h = n_ $i^{2}$ — product of electron and hole concentrations equals the square of the intrinsic carrier concentration; valid for all semiconductor types
p-n junction	Interface formed by joining p-type and n-type semiconductor materials; forms the basis of diodes and transistors
Depletion region	The region near the p-n junction depleted of free charge carriers, containing only immobile ionized donor and acceptor atoms
Barrier potential (built-in potential)	The potential difference across the depletion region that prevents further diffusion of majority carriers; ~0.7 V for Si, ~0.3 V for Ge
Forward bias	External voltage applied with positive terminal to p-side and negative to n-side; reduces barrier potential, narrows depletion region, allows current
Reverse bias	External voltage applied with positive terminal to n-side and negative to p-side; increases barrier potential, widens depletion region, blocks current
Knee voltage	The forward bias voltage at which the diode current begins to rise sharply; approximately equals the barrier potential (~0.7 V Si, ~0.3 V Ge)
Zener diode	A heavily doped p-n junction diode designed to operate in reverse breakdown at a stable voltage V_Z; used as a voltage regulator
Photodiode	A p-n junction diode operated in reverse bias; incident photons generate electron-hole pairs, producing a photocurrent proportional to light intensity
LED (Light Emitting Diode)	A forward-biased p-n junction diode in which recombination of electrons and holes releases energy as photons; wavelength determined by E_g
Solar cell	A large-area p-n junction that converts light energy directly to electrical energy via the photovoltaic effect; requires no external bias
Rectifier	A circuit using diodes to convert alternating current (AC) to direct current (DC); half-wave uses 1 diode, full-wave uses 2 or 4
Universal gate	A logic gate (NAND or NOR) from which any other Boolean logic gate or function can be constructed
De Morgan's theorem	A pair of Boolean algebra identities: $\overline{A+B} = \overline{A}\cdot\overline{B}$ and $\overline{A\cdot B} = \overline{A}+\overline{B}$
Truth table	A table listing all possible input combinations for a logic gate and their corresponding output values