alternating current: electric current that reverses direction periodically, usually many times per second.

ammeter: an instrument used for measuring the electrical current flow in a portion of a circuit.

atomic orbital: the region in space around the nucleus of an atom in which an electron with a given set of quantum numbers is most likely to be found.

band: a collection of orbitals, each delocalized throughout the solid, that are so closely spaced in energy as to be nearly continuous.

band gap: the energy separation between the top of the valence band and the bottom of the conduction band.

bias: voltage applied to the electrodes in an electrical device, considering polarity.

biasing: applying a voltage, often done to alter the electrical and optical output of a device such as a light emitting diode (LED).

charge coupled devices: a charge transfer device that stores charge in potential wells and transfers it almost completely as a packet by translating the position of the potential well.

choke coil: an inductance device used in a circuit to present a high impedance to high frequencies without appreciably limiting the flow of direct current.

cleaved-coupled-cavity (C[3]): two or more aligned semiconductor lasers which through destructive and constructive interference are able to output light of a particular wavelength.`

conduction band: the unfilled energy levels into which electrons can be excited to become conductive electrons; a band that when partially occupied by mobile electrons, permits their net movement in a particular direction, producing the flow of electricity through the solid.

conductor: a material with a high electrical conductivity such as copper or aluminum.

crystal: a solid composed of atoms, ions, or molecules arranged in an orderly pattern that is repeated in three dimensions.

delocalized (electrons): electrons that are no longer bound to a given atomic nucleus and are highly mobile.

diode: a two electrode semiconductor device that utilizes the rectifying properties of a p-n junction or a point contact.

direct current: electric current which flows in one direction only.

dopant: an impurity element that is deliberately added to a semiconductor.

drift velocity: the average velocity of a carrier that is moving under the influence of an electric field in a conductor, semiconductor, or electron tube.

electrical conductivity: the ability of a material to carry an electric current; it is the reciprocal of resistivity with units of ohm [-1] cm[-1].

electrical resistance: the measure of the difficulty of electric current to pass through a given material; its unit is the ohm ([[Omega]]).

electricity: current passing through a conductor from a region of high potential to low potential.

electric generator: a device which takes mechanical energy as an input and produces electricity (AC/DC) as an output.

electromagnetic radiation (waves): a series of energy waves that travel in a vacuum at the speed of 3 x 10[8] m/s; includes radio waves, microwaves, visible light, infrared, and ultraviolet light, x-rays, and gamma rays.

electron: a negatively charged sub-atomic particle whose mass is 9.1 x 10[-31] kg.

electron energy level: In quantum mechanics, an energy which is allowed for an electron.

electronics: a branch of applied physics and engineering concerned with controlling the movement of electrons in circuits.

extrinsic semiconductor: a semiconductor material that has been doped with an n-type or p-type element.

forward bias: bias applied to a p-n junction in the conducting direction, majority carrier electrons and holes flow toward the junction so that a large current flows.

galvanometer: an instrument for measuring a small electric current

germanium: element 22, used mostly in early semiconductor devices.

hole: a fictitious mobile particle that behaves as though it is a positively charged particle; holes are produced in the valence band when electrons from the valence band are promoted to the conduction band or an acceptor level of a p-type dopant.

incandescent light: a gas filled (argon) bulb containing a metallic filament (tungsten) that produces light when a sufficient voltage is applied; an ordinary light bulb.

insulator: a material with a low electrical conductivity; a type of material having a lower energy valence band that is nearly completely filled with electrons and a higher conduction band that is nearly completely empty of electrons as a result of a large energy gap between the two bands.

integrated circuit (IC): a single semiconductor chip or wafer which now contains thousands or millions of circuit elements per square centimeter.

intrinsic semiconductors: a semiconductor material that is essentially pure.

laser diode: a solid-state semiconductor device that is capable of emitting coherent light.

leads: wire segments used to connect devices in electric circuits.

light emitting diode (LED) : a semiconductor p-n junction device that is optimized to release light of approximately the band gap energy when electrons fall from the conduction band to the valence band.

metal: a material with a partially filled energy band; metals are generally malleable, ductile, good reflectors of electromagnetic radiation, and good conductors of heat and electricity; metals are usually identified by having electrical conductivities that decrease with increasing temperature.

monolithic IC technology: a technique of circuit fabrication where all of the devices in a circuit are placed on the same chip.

multimeter: a volt-ohm-milliammeter combined into one device

n-type semiconductor: a semiconductor that has been doped with an electron donor.

ohmmeter: an instrument for measuring electric resistance.

opto-electronic: materials that can either produce an electric current from light or produce light from a current.

photocell: a solid state photosensitive device whose current-voltage characteristic is a function of incident radiation; "electric eye" or "photoelectric cell".

photoconductivity: light shining on the surface of a material increasing the conductivity.

photon: a massless particle, the quantum of the electromagnetic field carrying energy, also known as the light quantum.

photoresistor: a device for measuring or detecting electromagnetic radiation. The conductivity of the resistor changes with exposure to light.

p-n junction: a boundary between p-type and n-type regions within a single crystal of a semiconductor material, a diode.

p-type semiconductor: a semiconductor that has been doped with an electron acceptor.

quantum mechanics: physical laws governing the behavior of matter and energy on a very small scale.

quantum numbers: a set of four numbers necessary to fully characterize the state of each electron in an atom.

rectifier: a circuit component, usually a diode, that allows current to flow in one direction unimpeded but allows no current flow in the other direction.

resistor: a device used in electric circuits to limit the current flow or to provide a voltage drop.

reverse bias: bias applied to a p-n junction in a direction for which the flow of current is inhibited; majority carrier electrons and holes flow away from the junction.

semiconductor: a material whose electrical conductivity is midway between that of an good conductor and a good insulator; a type of material having a lower energy valence band that is nearly completely filled with electrons and a higher energy conduction band that is nearly completely empty of electrons, with a modest energy gap between the two bands; pure materials usually exhibit electrical conductivity that increases with temperature because of an increase in the number of charge carriers being promoted to the conduction band.

silicon: element 14, the most commonly used semiconductor.

thermistor: a resistive circuit component having a high negative temperature coefficient of resistance so that its resistance decreases as temperature increases.

transformer: a magnetic coupling device in an AC circuit; they are capable of changing voltages as needed.

transistor: a solid state semiconductor device able to amplify a signal in forward bias.

valence band: the energy band containing the valence (outer) electrons; in a conductor the valence band is also the conduction band; the valence band in a metal is not full, so electrons can be energized to other levels and become conductive.

voltmeter: an instrument used for measuring the potential difference between two points in volts.