Semiconductor glossary of terms

Acceptor: a dopant atom with a lower valence than the host material atoms. Acceptor atoms add energy levels above the valence band.

Alloyed Semiconductor: semiconductor material where proportion of the atoms occupying the lattice sites are replaced with another element from the same group in order to obtain more desirable material properties such as lattice matching or energy gap. More than one element may be substituted, allowing control of lattice spacing and energy gap.

Active Region: layer of semiconductor material where radiative recombination takes place. Also active layer.

Bandwidth: The range of frequency of a signal or signal-carrying channel. For digital signals, the width is expressed as the data transfer rate, in bits per second. In semiconductor devices, the bandwidth is the frequency range in which the performance characteristics fall within specified limits.

Base: The region of a bipolar transistor that separates the emitter and collector regions.

Bipolar transistor: Commonly used for amplification, a bipolar transistor is made from a sandwich of N- and P-type semiconductor material, resulting in either a PNP or NPN transistor. The middle section is known as the "base" and the other two as the "collector" and "emitter." In P-type material, electric charges are carried mainly in the form of electron deficiencies called holes. In N-type material, the charge carriers are primarily electrons. Bipolar devices can switch signals at high speeds, and can be manufactured to handle large currents, making them useful for applications such as high-power amplifiers in wireless transmitters.

Carrier Density: the volume density of mobile charge carriers in a semiconductor material.

Carrier Mobility: a measure of the average speed of a carrier in a given semiconductor, given by the average drift velocity of the carrier per unit electric field.

Circuit: An assemblage of interconnected electrical or electronic components.

Clean room: A room in which the climate and particulate matter are precisely controlled. Clean rooms are "classed" according to a maximum number of particles (0.3 micron or larger) that may exist in any one cubic foot of space within the defined area. A Class 1 clean room is limited to only one particle in a cubic foot of space.

Compound Semiconductor: a semiconductor substance that is composed of two or more elements that are chemically combined such as GaAs, InP, GaN, GaNAs, GaInNAs.

Conduction Band: an energy band in a solid in which electrons are freely mobile and can produce a net electric current.

Conductor: Any material that offers little resistance to the flow of electrical current (e.g., aluminum, copper, gold).

Donor: dopant atom with a valence higher than of the host material atoms. Donor atoms add energy levels below the conduction band.

Donor Level: an intermediate energy level close to the conduction level in a semiconductor; filled at absolute zero, the electrons in this level can acquire energies corresponding to the conduction level at other temperatures.

Doping: The process of introducing small, precisely controlled quantities of specific elements into single crystal semiconductors. The fundamental purpose of doping is to engineer the electrical properties of the semiconductor (e.g. resistivity, carrier concentration), as part of the manufacture of solid state devices. The lacing of an intrinsic semiconductor material with another type of atom to change the propulation of either positive or negative charge carriers, see also N-type and P-type semiconductors.

Electron-Hole Pair: a conduction electron in the conduction band and an accompanying electron hole in the valence band, which result when an electron jumps the gap in an intrinsic semiconductor.

Electron-Hole Recombination: a process in which a hole is recombined with an electron within a doped semiconductor, accompanied by a release of energy, typically in the form of radiation.

Electronic Work Function: the energy required to remove an electron with the Fermi energy in a solid to the energy level of an electron at rest in vacuum outside the solid.

Elemental Semiconductor: a semiconductor material formed by a single type of atom. Examples include, Silicon and Germanium

Energy gap: a range of forbidden energy levels between two permitted bands.

Epitaxial layer: a layer of semiconductor material having the same crystalline orientation as that of the substrate upon which it is grown.

Epitaxy: The growth on a crystalline substrate of a crystalline layer, called an epilayer, that mimics the orientation of the substrate.

Etch: To remove, in a controlled manner, selected material from a wafer by employing chemical, electrolytic, or plasma means.

Extrinsic Semiconductor: semiconductor material intentionally doped with impurity atoms to create vacancies for electrons known as holes or add electrons to material.

Fab: Fabrication. In semiconductor manufacturing, specifically the front-end process of making devices and integrated circuits in semiconductor wafers.

Fermi Level: the Fermi level is the energy at which the probability of occupation by an electron is exactly one half.

FET: Field-effect transistor. Transistors, commonly used for weak-signal amplification, in which the output current is varied by varying the value of an electric field within a region of the device. A FET has a region of donor material with two terminals called the "source" and the "drain," with a region of acceptor material, called the "gate," lying between. The gate is so called because it can be used to control the flow of electrons along the channel.

Filled Band: an energy-level band in which there are no vacancies, and the electrons do not contribute to valence or conduction processes.

Forbidden Band: a gap between two bands of allowed energy levels in a crystalline solid. Also Energy gap.

GaAs: Gallium arsenide. A III-V compound semiconductor material used for making optoelectronic devices and high-frequency ICs. The charge carriers, mostly electrons, move at high speed among the atoms (twice the speed of those of silicon), making GaAs components useful for producing higher-speed devices. Also, GaAs devices generate less noise than most other types of semiconductor components, important for weak-signal amplification.

Gate: The control electrode in a field-effect transistor (FET). The application of a voltage to the gate varies the electrical diameter of the semiconductor path or channel, allowing the regulation of its conducting properties.

Growth process: The process of making device wafers by depositing, or "growing," layer by layer, on a substrate.

Hole: Vacancy created by the addition of acceptors to the host material to generate a weakly attractive trap for an electron.

Impurity: a substance that is incorporated into a semiconductor material and provides free electrons (n-type impurity) or holes (p-type impurity).

Impurity Band: an energy level, associated with the energy of a set of impurities in a solid, that is not part of the normal band scheme.

Impurity Scattering: non-radiative scattering mechanism where electrons lose energy in the form of phonon by scattering off impurity atoms in the semiconductor crystal.

Insulator: a material in which all the electrons lie in the valance band and the energy gap is too large for electrons to occupy available higher energy levels when a potential difference is applied. See also CONDUCTOR and SEMICONDUCTOR

Indirect Gap Semiconductor: a semiconductor in which the minimum in the conduction band and the maximum in the valence band occur at different locations in reciprocal space; their energy difference defines the band-gap energy.

Intrinsic Semiconductor: a semiconductor that has no impurities to change the conduction properties of the material. Also, I-type semiconductor.

InGaP: Indium gallium phosphide. Used in HBT device wafers. A III-V compound semiconductor material used for making optoelectronic devices and high-frequency ICs. This material is often employed in very high-speed, reliable HBTs, FETs, and lasers.

Integrated Circuit (IC): Sometimes called a chip or microchip, an IC is a small electronic device (consisting of thousands or millions of tiny resistors, capacitors, and transistors) made from a semiconducting material. Devices containing integrated circuits have a variety of applications including microprocessors, audio and video equipment, and automobiles.

Lattice: a regularly space array of points that represents the structure of a crystal. Crystals are composed of groups of atoms repeated at regular interval in three dimensions with the same orientation. Each such group of atoms is replaced by a representative point; the collection of points so formed is the space lattice or lattice of the crystal. Each crystal lattice is a Bravais lattice.

Lattice-matching: of alloyed semiconductors. For epitaxial growth of layers of differing semiconductor material without dislocations, it is necessary to choose an alloy composition with a similar lattice spacing to that of the substrate material.

Lattice Scattering: the electron scattering that occurs within a crystal due to vibrations in the lattice structure.

Lattice Vibration: a regular vibration of atoms in a crystal lattice about their equilibrium positions.

LASER: Light Amplification by the Stimulated Emission of Radiation

Low Noise Amplifier (LNA): Integrated circuits (ICs) used to amplify lower-power, smaller signals into larger, more easily used signals. LNAs are designed to contribute very little noise.

N-type semiconductor: A semiconductor in which current is conducted by excess free electrons.

Optoelectronic: Pertaining to any device that functions as an electrical-to-optical or optical-to-electrical

Transducer: a device that is responsive to or that emits or modifies light waves, or an instrument that uses such a device in its operation.

p-n junction: semiconductor material doped in with donors and acceptors to form a sharply defined region with over which the doping type changes from p to n. A single p-n junction acts as a diode. More complicated arrangements of p-n junctions form the basis of many semiconductor devices such as transistors, LED's and the first inefficient semiconductor lasers.

P-type semiconductor: A semiconductor in which current is conducted by electron vacancies. Semiconductor material doped with acceptors to create 'holes'.

Photodetectors: Semiconductor devices that receive light and convert it into electrical signals.

Photoluminescence: A method of measuring some critical semiconductor material characteristics by shining a laser on the material and measuring the signal that returns.

Power amplifiers: Integrated circuits (ICs) used to amplify lower-power, smaller signals into larger, more easily used signals. Power amplifiers are designed to handle high power levels.

Profilometry: A method for measuring the profile, or heights, of semiconductor layers by dragging a needle across the surface of an etched semiconductor.

Resistivity mapping: A method to map the resistance of a semiconductor across an entire wafer.

Semiconductor: A material, usually a solid chemical element or compound, that is neither a good conductor of electricity (like copper) nor a good insulator (like rubber). The conductance varies depending on the current or voltage applied to a control electrode, or on the intensity of irradiation by infrared, visible, or ultraviolet light, or X rays. Common semiconductors include silicon, germanium, gallium arsenide, indium antimonide, and the oxides of most metals. Of these, gallium arsenide (GaAs) is widely used in low-noise, high-gain, weak-signal amplifying devices.

Substrate: The underlying material on which other layers are deposited. Such material may be electrically active, such as gallium arsenide or silicon, or passive, such as alumina ceramic.

Transistor: A three-terminal device composed of semiconductor material that amplifies a signal or opens or closes a circuit. Transistors are the basic elements in integrated circuits, which consist of very large numbers of transistors interconnected with circuitry and contained within a single "chip." Note: John Bardeen, an engineering professor at the University of Illinois at Urbana-Champaign, was awarded his first Nobel Prize for developing the transistor while at Bell Labs.

Valence Band: the highest occupied energy level in a solid crystal semiconductor or insulator that is occupied by electrons at T= 0K.

Wafer: A thin semiconductor material (approximately 1/30" thick) used as the foundation for integrated circuit manufacture.

KEY

UNIT 1

SEMICONDUCTORS