Semiconductor 9-12

anisotype junction

A heterojunction in which the type of dopant changes at the metallurgical junction.

electron affinity rule

The rule stating that, in an ideal heterojunction, the discontinuity at the conduction band is the difference between the electron affinities in the two semiconductors.

heterojunction

The junction formed by the contact between two different semiconductor materials.

image force–induced lowering

The lowering of the peak potential barrier at the metal–semiconductor junction due to an electric field.

isotype junction

A heterojunction in which the type of dopant is the same on both sides of the junction.

ohmic contact

A low-resistance metal–semiconductor contact providing conduction in both directions between the metal and semiconductor.

Richardson constant

The parameter A* in the current–voltage relation of a Schottky diode.

Schottky barrier height

The potential barrier Bn from the metal to semiconductor in a metal–semiconductor junction.

Schottky effect

Another term for image force–induced lowering.

specific contact resistance

The inverse of the slope of the J versus V curve of a metal–semiconductor contact evaluated at V=0.

thermionic emission

The process by which charge flows over a potential barrier as a result of carriers with sufficient thermal energy.

tunneling barrier

A thin potential barrier in which the current is dominated by the tunneling of carriers through the barrier.

two-dimensional electron gas (2-DEG)

The accumulation layer of electrons contained in a potential well at a heterojunction interface. The electrons are free to move in the “other” two spatial directions.

accumulation layer charge

The induced charge directly under an oxide that is in excess of the thermal-equilibrium majority carrier concentration.

channel conductance

The ratio of drain current to drain-to-source voltage in the limit as VDS → 0.

channel conductance modulation

The process whereby the channel conductance varies with gate-to-source voltage.

CMOS

the technology that uses both p- and n-channel devices in an electronic circuit fabricated in a single semiconductor chip.

conduction parameter

The multiplying coefficient of the voltage terms to obtain the MOSFET drain current.

cutoff frequency

The signal frequency at which the input ac gate current is equal to the output ac drain current.

depletion mode MOSFET

The type of MOSFET in which a gate voltage must be applied to turn the device off.

enhancement mode MOSFET

The type of MOSFET in which a gate voltage must be applied to turn the device on.

equivalent fixed oxide charge

The effective fixed charge in the oxide, Qss, directly adjacent to the oxide–semiconductor interface.

field-effect

The phenomenon by which an electric field perpendicular to the surface of a semiconductor can modulate the conductance.

flat-band voltage

The gate voltage that must be applied to create the flat-band condition in which there is no space charge region in the semiconductor under the oxide.

interface states

The allowed electronic energy states within the bandgap energy at the oxide–semiconductor interface.

inversion layer charge

The induced charge directly under the oxide, which is the opposite type compared with the semiconductor doping.

inversion layer mobility

The mobility of carriers in the inversion layer.

metal–semiconductor work function difference

The parameter ms, a function of the difference between the metal work function and semiconductor electron affinity.

oxide capacitance

The ratio of oxide permittivity to oxide thickness, which is the capacitance per unit area, Cox.

process conduction parameter

The product of carrier mobility and oxide capacitance.

saturation

The condition in which the inversion charge density is zero at the drain and the drain current is no longer a function of the drain-to-source voltage.

strong inversion

The condition in which the inversion charge density is larger than the magnitude of the semiconductor doping concentration.

threshold inversion point

The condition in which the inversion charge density is equal in magnitude to the semiconductor doping concentration.

threshold voltage

The gate voltage that must be applied to achieve the threshold inversion point.

transconductance

The ratio of an incremental change in drain current to the corresponding incremental change in gate voltage.

weak inversion

The condition in which the inversion charge density is less than the magnitude of the semiconductor doping concentration.

channel length modulation

The change in effective channel length with drain-to-source voltage when the MOSFET is biased in saturation.

drain-induced barrier lowering

The near punch-through condition in which the potential barrier between the source and channel region in an off transistor is lowered due to a large applied drain voltage.

hot electrons

Electrons with energies far greater than the thermal-equilibrium value caused by acceleration in high electric fields.

lightly doped drain (LDD)

A MOSFET with a lightly doped drain region adjacent to the channel to reduce voltage breakdown effects.

narrow-channel effects The shift in threshold voltage as the channel width narrows.

near punch-through

The reduction in the potential barrier between source and substrate by the drain-to-substrate voltage, resulting in a rapid increase in drain current.

short-channel effects

The shift in threshold voltage as the channel length becomes smaller.

snapback

The negative resistance effect during breakdown in a MOSFET caused by the variable current gain in a parasitic bipolar transistor.

subthreshold conduction

The process of current conduction in a MOSFET when the transistor is biased below the threshold inversion point.

surface scattering

The process of electric field attraction and coulomb repulsion of carriers at the oxide–semiconductor interface as the carriers drift between source and drain.

threshold adjustment

The process of altering the threshold voltage by changing the semiconductor doping concentration through ion implantation.

alpha cutoff frequency

The frequency at which the magnitude of the common-base current is 12 of its low-frequency value; also equal to the cutoff frequency.

bandgap narrowing

The reduction in the forbidden energy bandgap with high emitter doping concentration.

base transit time

The time that it takes a minority carrier to cross the neutral base region.

base transport factor

The factor in the common-base current gain that accounts for recombination in the neutral base width.

base width modulation

The change in the neutral base width with C–E or C–B voltage.

beta cutoff frequency

The frequency at which the magnitude of the common-emitter current gain is 12 of its low-frequency value.

collector capacitance charging time

The time constant that describes the time required for the B–C and collector–substrate space charge widths to change with a change in emitter current.

collector depletion region transit time

The time that it takes a carrier to be swept across the B–C space charge region.

common-base current gain

The ratio of collector current to emitter current.

common-emitter current gain

The ratio of collector current to base current.

current crowding

The nonuniform current density across the emitter junction area created by a lateral voltage drop in the base region due to a finite base current and base resistance.

cutoff

The bias condition in which zero- or reverse-biased voltages are applied to both transistor junctions, resulting in zero transistor currents.

cutoff frequency

The frequency at which the magnitude of the common-emitter current gain is unity.

early effect

Another term for base width modulation.

early voltage

The value of voltage (magnitude) at the intercept on the voltage axis obtained by extrapolating the IC versus VCE curves to zero current.

emitter–base junction capacitance charging time

The time constant describing the time for the B–E space charge width to change with a change in emitter current.

emitter injection efficiency factor

The factor in the common-base current gain that takes into account the injection of carriers from the base into the emitter.

forward active

The bias condition in which the B–E junction is forward biased and the B–C junction is reverse biased.

inverse active

The bias condition in which the B–E junction is reverse biased and the B–C junction is forward biased.

output conductance

The ratio of a differential change in collector current to the corresponding differential change in C–E voltage.