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Term (Index) Definition
bandgap  energy gap (Eg) in semiconductors and insulators; forbidden energy levels separating valence band and conduction band; no electrons are allowed at these levels; no bandgap in metals.
energy gap, forbidden band, bandgap, Eg  energy band separating conduction and valence bands in the solid; no electron energy levels are allowed in the forbidden band; no energy gap in metals in which case conduction and valence bands overlap; solids featuring energy gap are defined as either semiconductors or insulators based on the width of energy gap; values of Eg (at 300K) for common semiconductors: InSb - 0.17 eV, Ge - 0.67 eV, Si - 1.12 eV, GaAs - 1.43 eV GaP - 2.26 eV, 6H-SiC - 2.9 eV, GaN - 3.5 eV, and insulators Ta2O5 - 4.2 eV , TiO2 -5 eV, Si3N4 - 5.1, Al2O3 ~5 eV, SiO2 - 8.0
Term (Index) Definition
bandgap engineering  processes in which energy gap of semiconductor is altered in the desired way by changing chemical composition of semiconductor; e.g. by adding Al bandgap of GaAs can be altered; used in superlattice fabrication.
Molecular Beam Epitaxy, MBE  physical deposition process (basically evaporation) carried out in ultra-high vacuum (below 10-8 torr) and at substrate temperature typically not exceeding 800 oC; due to unobstructed (molecular) flow of species to be deposited and chemical cleanliness of the substrate surface highly controlled growth of ultra-thin epitaxial layers is possible; the highest precision deposition method used in semiconductor processing.
superlattice  semiconductor structure comprising of several ultra-thin layers (atomic layers) engineered to obtain specific electronic and photonic properties; slight modifications of chemical composition of each layer result in slight variations of energy bandgap from layer to layer: bandgap engineering; fabrication of superlattices requires high-precision heteroepitaxial deposition methods such as MBE and MOCVD; typically involves III-V semiconductors.
Term (Index) Definition
direct bandgap semiconductor  semiconductor in which the bottom of the conduction band and the top of the valence band occur at the momentum k=0;in the case of d.b.s. energy released during band-to-band electron recombination with a hole is converted primarily into radiation (radiant recombination); wavelength of emitted radiation is determined by the energy gap of semiconductor; examples of d.b.s. GaAs, InP, etc.
indirect bandgap semiconductor  semiconductor in which bottom of the conduction band does not occur at effective momentum k=0, i.e. is shifted with respect to the top of the valence band which occurs at k=0; energy released during electron recombination with a hole is converted primarily into phonon; e.g. Si, Ge, GaP.
Term (Index) Definition
energy gap, forbidden band, bandgap, Eg  energy band separating conduction and valence bands in the solid; no electron energy levels are allowed in the forbidden band; no energy gap in metals in which case conduction and valence bands overlap; solids featuring energy gap are defined as either semiconductors or insulators based on the width of energy gap; values of Eg (at 300K) for common semiconductors: InSb - 0.17 eV, Ge - 0.67 eV, Si - 1.12 eV, GaAs - 1.43 eV GaP - 2.26 eV, 6H-SiC - 2.9 eV, GaN - 3.5 eV, and insulators Ta2O5 - 4.2 eV , TiO2 -5 eV, Si3N4 - 5.1, Al2O3 ~5 eV, SiO2 - 8.0
conduction band  the upper energy band in semiconductor separated by the energy gap (bandgap)from the valance band; c.b. is not completely filled with electrons, hence, electrons can conduct in the conduction band.
valence band  energy band in semiconductor that is filled with electrons at 0 K; electrons cannot conduct in valence band.
Term (Index) Definition
indirect bandgap semiconductor  semiconductor in which bottom of the conduction band does not occur at effective momentum k=0, i.e. is shifted with respect to the top of the valence band which occurs at k=0; energy released during electron recombination with a hole is converted primarily into phonon; e.g. Si, Ge, GaP.
direct bandgap semiconductor  semiconductor in which the bottom of the conduction band and the top of the valence band occur at the momentum k=0;in the case of d.b.s. energy released during band-to-band electron recombination with a hole is converted primarily into radiation (radiant recombination); wavelength of emitted radiation is determined by the energy gap of semiconductor; examples of d.b.s. GaAs, InP, etc.
Term (Index) Definition
wide bandgap semiconductor  semiconductor featuring energy gap Eg > 2.5 eV (rather arbitrary criterion), useful in high temperature applications and emission of blue radiation (should feature direct bandgap at the same time); e.g. SiC (Eg = 2.9 eV), GaN (Eg = 3.5 eV), ZnS (Eg = 3.68 eV)
gallium nitride, GaN  wide bandgap III-V semiconductor featuring direct bandgap 3.5 eV wide; among very few semiconductors capable of generating blue radiation; number one candidate for blue LEDs and lasers; see "GaN note" on www.semiconductornotes.com for more information.

Reference: See Semiconductor Notes for more information on GaN
silicon carbide, SiC  semiconductor featuring energy gap Eg = 2.9 -3.05 eV (wide bandgap semiconductor), indirect bandgap; SiC can be obtained in several polytypes- most common hexagonal in the form of either 4H or 6H polytypes; parameters vary depending on polytype; higher than Si and GaAs electron saturation velocity; carrier mobility: electrons 100-500 cm2/Vs, holes 20 cm2/Vs; thermal conductivity 3 W/cmK (two times higher than Si); excellent semiconductor, however, difficult and expensive to fabricate in the form of single-crystal wafers; best suited for high power, high temperature devices; also limited use in photonic devices (e.g. substrate for GaN).

Reference: SemiOneSource,Notes
Zinc sulfide, ZnS  II-VI semiconductor, has a largest bandgap among semiconductors considered for practical applications (Eg = 3.68 eV) which in conjunctions with a bandgap being direct makes ZnS potentially attractive as a blue light emitter.
diamond  single-crystal carbon; material featuring outstanding semiconductor properties; wide bandgap semiconductor; in theory the best semiconductor, in practice very difficult to form in shapes and quantities compatible with manufacturing of semiconductor devices; also, restrictions on p-n junction formation due to the lack of adequate dopants.

Reference: More information on semiconductor materials
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Jerzy Ruzyllo is a Distinguished Professor Emeritus in the Department of Electrical Engineering at Penn State University.



This book gives a complete account of semiconductor engineering covering semiconductor properties, semiconductor materials, semiconductor devices and their uses, process technology, fabrication processes, and semiconductor materials and process characterization.


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Created and operated by J. Ruzyllo. Copyright © J. Ruzyllo 2001-2016. All rights reserved.

Information in this glossary is provided at the author's discretion. Any liability based on, or related to the contents of this glossary is disclaimed.