Semiconductor Chapter 5-8

conductivity

A material parameter related to carrier drift; quantitatively, the ratio of drift current density to electric field.

diffusion

The process whereby particles flow from a region of high concentration to a region of low concentration.

diffusion coefficient

The parameter relating particle flux to the particle density gradient.

diffusion current

The current that results from the diffusion of charged particles.

drift

The process whereby charged particles move while under the influence of an electric field.

drift current

The current that results from the drift of charged particles.

drift velocity

The average velocity of charged particles in the presence of an electric field.

Einstein relation

The relation between the mobility and the diffusion coefficient.

Hall voltage

The voltage induced across a semiconductor in a Hall effect measurement.

ionized impurity scattering

The interaction between a charged carrier and an ionized impurity center.

lattice scattering

The interaction between a charged carrier and a thermally vibrating lattice atom.

mobility

The parameter relating carrier drift velocity and electric field.

resistivity

The reciprocal of conductivity; a material parameter that is a measure of the resistance to current.

velocity saturation

The saturation of carrier drift velocity with increasing electric field.

ambipolar diffusion coefficient

The effective diffusion coefficient of excess carriers.

ambipolar mobility

The effective mobility of excess carriers.

ambipolar transport

The process whereby excess electrons and holes diffuse, drift, and recombine with the same effective diffusion coeffi cient, mobility, and lifetime.

ambipolar transport equation

The equation describing the behavior of excess carriers as a function of time and space coordinates.

carrier generation

The process of elevating electrons from the valence band into the conduction band, creating an electron-hole pair.

carrier recombination

The process whereby an electron "falls" into an empty state in the valence band (a hole) so that an electron-hole pair is annihilated.

excess carriers

The term describing both excess electrons and excess holes.

excess electrons

The concentration of electrons in the conduction band over and above the thermal-equilibrium concentration.

excess holes

The concentration of holes in the valence band over and above the thermal-equilibrium concentration.

excess minority carrier lifetime

The average time that an excess minority carrier exists before it recombines.

generation rate

The rate (#/cm3-s) at which electron-hole pairs are created.

low-level injection

The condition in which the excess carrier concentration is much smaller than the thermal-equilibrium majority carrier concentration.

minority carrier diffusion length

The average distance a minority carrier diffuses before recombining: a parameter equal to sqrt(D*tau) where D and tau are the minority carrier diffusion coefficient and lifetime, respectively.

quasi-Fermi level

The quasi-Fermi level for electrons and the quasi-Fermi level for holes relate the nonequilibrium electron and hole concentrations, respectively, to the intrinsic carrier concentration and the intrinsic Fermi level.

recombination rate

The rate (#/cm3-s) at which electron-hole pairs recombine.

surface recombination velocity

A parameter that relates the gradient of the excess carrier concentration at a surface to the surface concentration of excess carriers.

surface states

The electronic energy states that exist within the bandgap at a semiconductor surface.

abrupt junction approximation

The assumption that there is an abrupt discontinuity in space charge density between the space charge region and the neutral semiconductor region.

avalanche breakdown

The process whereby a large reverse-biased pn junction current is created due to the generation of electron-hole pairs by the collision of electrons and/or holes with atomic electrons within the space charge region.

built-in potential barrier

The electrostatic potential difference between the p and n regions of a pn junction in thermal equilibrium.

critical electric field

The peak electric fi eld in the space charge region at breakdown.

depletion layer capacitance

Another term for junction capacitance.

depletion region

Another term for space charge region.

hyperabrupt junction

A pn junction in which the doping concentration on one side decreases away from the metallurgical junction to achieve a specific capacitance- voltage characteristic.

junction capacitance

The capacitance of the pn junction under reverse bias.

linearly graded junction

A pn junction in which the doping concentrations on either side of the metallurgical junction are approximated by a linear distribution.

metallurgical junction

The interface between the p- and n-doped regions of a pn junction.

one-sided junction

A pn junction in which one side of the junction is much more heavily doped than the adjacent side.

reverse bias

The condition in which a positive voltage is applied to the n region with respect to the p region of a pn junction so that the potential barrier between the two regions increases above the thermal-equilibrium built-in potential barrier.

space charge region

The region on either side of the metallurgical junction in which there is a net charge density due to ionized donors in the n region and ionized acceptors in the p region.

space charge width

The width of the space charge region, a function of doping concentrations and applied voltage.

varactor diode

A diode whose reactance can be varied in a controlled manner with bias voltage.

carrier injection

The flow of carriers across the space charge region of a pn junction when a voltage is applied.

diffusion capacitance

The capacitance of a forward-biased pn junction due to minority carrier storage effects.

diffusion conductance

The ratio of a low-frequency, small-signal sinusoidal current to voltage in a forward-biased pn junction.

diffusion resistance

The inverse of diffusion conductance.

forward bias

The condition in which a positive voltage is applied to the p region with respect to the n region of a pn junction so that the potential barrier between the two regions is lowered below the thermal-equilibrium value.

generation current

The reverse-biased pn junction current produced by the thermal generation of electron-hole pairs within the space charge region.

high-level injection

The condition in which the excess carrier concentration becomes comparable to or greater than the majority carrier concentration.

"long" diode

A pn junction diode in which both the neutral p and n regions are long compared with the respective minority carrier diffusion lengths.

recombination current

The forward-bias pn junction current produced as a result of the flow of electrons and holes that recombine within the space charge region.

reverse saturation current

The ideal reverse-biased current in a pn junction.

"short" diode

A pn junction diode in which at least one of the neutral p or n regions is short compared to the respective minority carrier diffusion length.

storage time

The time required for the excess minority carrier concentrations at the space charge edge to go from their steady-state values to zero when the diode is switched from forward to reverse bias.