241:. Commonly used experimental techniques to investigate band-gap can be sensitive to many things such as the size of the band-gap, electronic structure features (direct versus indirect gap) and also the number of free charge carriers (which can frequently depend on synthesis conditions). Band-gap obtained from transport property modeling is essentially independent of such factors. Theoretical techniques to calculate the electronic structure on the other hand can often underestimate band-gap.
27:
195:, this is true at very low temperatures but at higher temperatures the carrier density increases with temperature giving rise to a semimetal-semiconductor transition. A semimetal also differs from an insulator or semiconductor in that a semimetal's conductivity is always non-zero, whereas a semiconductor has zero conductivity at zero temperature and insulators have zero conductivity even at ambient temperatures (due to a wider band gap).
250:
183:(as more electrons are shifted to the conduction band), before decreasing with intermediate temperatures and then, once again, increasing with still higher temperatures. The semimetallic state is similar to the metallic state but in semimetals both holes and electrons contribute to electrical conduction. With some semimetals, like
178:
and electrons), both the carrier mobilities and carrier concentrations will contribute to the conductivity and these have different temperature dependencies. Ultimately, it is observed that the conductivity of insulators and semiconductors increase with initial increases in temperature above
308:, semimetals have charge carriers of both types (holes and electrons), so that one could also argue that they should be called 'double-metals' rather than semimetals. However, the charge carriers typically occur in much smaller numbers than in a real metal. In this respect they resemble
236:
VAl for example, was historically thought of as a semi-metal (with a negative gap ~ -0.1 eV) for over two decades before it was actually shown to be a small-gap (~ 0.03 eV) semiconductor using self-consistent analysis of the transport properties, electrical resistivity and
332:. They also have small effective masses for both holes and electrons because the overlap in energy is usually the result of the fact that both energy bands are broad. In addition they typically show high
488:
Anand, Shashwat; Gurunathan, Ramya; Soldi, Thomas; Borgsmiller, Leah; Orenstein, Rachel; Snyder, Jeff (2020). "Thermoelectric transport of semiconductor full-Heusler VFe2Al".
232:
Classification of a material either as a semiconductor or a semimetal can become tricky when it has extremely small or slightly negative band-gaps. The well-known compound Fe
146:) than that of a semiconductor (e.g., < 4 eV). Because of the slight overlap between the conduction and valence bands, semimetals have no band gap and a small
601:
Reed, Evan J.; Manaa, M. Riad; Fried, Laurence E.; Glaesemann, Kurt R.; Joannopoulos, J. D. (2007). "A transient semimetallic layer in detonating nitromethane".
523:
Wang, Yang; N. Mansour; A. Salem; K.F. Brennan & P.P. Ruden (1992). "Theoretical study of a potential low-noise semimetal-based avalanche photodetector".
400:
are typically not considered metalloids. Transient semimetal states have been reported at extreme conditions. It has been recently shown that some
154:. A metal, by contrast, has an appreciable density of states at the Fermi level because the conduction band is partially filled.
297:
The figure is schematic, showing only the lowest-energy conduction band and the highest-energy valence band in one dimension of
214:
In a semimetal, the bottom of the conduction band is typically situated in a different part of momentum space (at a different
472:
170:. With a metal, the conductivity decreases with increases in temperature (due to increasing interaction of electrons with
702:
203:
To classify semiconductors and semimetals, the energies of their filled and empty bands must be plotted against the
95:
312:
more closely. This explains why the electrical properties of semimetals are partway between those of metals and
380:
but the terms semimetal and metalloid are not synonymous. Semimetals, in contrast to metalloids, can also be
138:. In insulators and semiconductors the filled valence band is separated from an empty conduction band by a
301:(or k-space). In typical solids, k-space is three-dimensional, and there are an infinite number of bands.
253:
This diagram illustrates a direct semiconductor (A), an indirect semiconductor (B), and a semimetal (C).
413:
211:
the conduction of electrons depends on the periodicity of the crystal lattice in different directions.
81:
39:
191:, there is a temperature-independent carrier density below room temperature (as in metals) while, in
174:(lattice vibrations)). With an insulator or semiconductor (which have two types of charge carriers –
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The insulating/semiconducting states differ from the semimetallic/metallic states in the
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142:. For insulators, the magnitude of the band gap is larger (e.g., > 4
707:
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As semimetals have fewer charge carriers than metals, they typically have lower
80:; however, in semiconductors the bands are near enough to the Fermi level to be
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221:) than the top of the valence band. One could say that a semimetal is a
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is a material with a small energy overlap between the bottom of the
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for a certain energy in the material listed. The shade follows the
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Filling of the electronic states in various types of materials at
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600:
558:
Wallace, P.R. (1947). "The Band Theory of
Graphite".
229:, although they are seldom described in those terms.
636:Bubnova, Olga; Zia, Ullah Khan; Wang, Hui (2014).
689:
635:
376:. The first two (As, Sb) are also considered
16:Metal with a small negative indirect band-gap
34:. Here, height is energy while width is the
273:a semiconductor with an indirect gap (like
207:of conduction electrons. According to the
157:
467:. Academic Press, Inc. pp. 339–40.
262:a semiconductor with a direct gap (e.g.
248:
25:
557:
690:
348:The classic semimetallic elements are
319:
462:
343:
525:IEEE Journal of Quantum Electronics
68:lies inside at least one band. In
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336:susceptibilities and high lattice
14:
719:
198:
490:Journal of Materials Chemistry C
257:Schematically, the figure shows
629:
594:
551:
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126:, solids can be classified as
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118:, but they do not overlap in
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76:the Fermi level is inside a
7:
407:
36:density of available states
10:
724:
414:Charge-transfer insulators
404:can behave as semimetals.
18:
310:degenerate semiconductors
703:Condensed matter physics
638:"Semi-Metallic Polymers"
90:intrinsic semiconductors
40:Fermi–Dirac distribution
19:Not to be confused with
168:electrical conductivity
88:. "intrin." indicates
50:: no state filled). In
580:10.1103/PhysRev.71.622
463:Burns, Gerald (1985).
330:thermal conductivities
264:copper indium selenide
254:
158:Temperature dependency
124:electronic band theory
100:
46:: all states filled,
290:alkaline earth metals
252:
29:
338:dielectric constants
166:dependency of their
654:2014NatMa..13..190B
615:2008NatPh...4...72R
572:1947PhRv...71..622W
537:1992IJQE...28..507W
496:(30): 10174–10184.
465:Solid State Physics
444:Solid-state physics
402:conductive polymers
320:Physical properties
239:Seebeck coefficient
114:and the top of the
82:thermally populated
502:10.1039/D0TC02659J
382:chemical compounds
344:Classic semimetals
280:a semimetal (like
255:
101:
84:with electrons or
474:978-0-12-146070-9
386:mercury telluride
304:Unlike a regular
148:density of states
134:, semimetals, or
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662:10.1038/nmat3824
642:Nature Materials
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364:(gray tin) and
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122:. According to
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603:Nature Physics
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566:(9): 622–634.
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531:(2): 507–513.
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434:Mott insulator
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299:momentum space
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199:Classification
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132:semiconductors
120:momentum space
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648:(2): 190–4.
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609:(1): 72–76.
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388:(HgTe), and
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116:valence band
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334:diamagnetic
164:temperature
152:Fermi level
60:Fermi level
32:equilibrium
692:Categories
450:References
419:Half-metal
384:, such as
378:metalloids
326:electrical
128:insulators
109:conduction
70:insulators
56:semimetals
21:Half-metal
698:Materials
678:205409397
510:225448662
370:allotrope
245:Schematic
105:semimetal
670:24317188
588:53633968
439:Nonmetal
408:See also
398:graphite
366:graphite
354:antimony
288:and the
286:graphite
284:(Sn) or
189:antimony
140:band gap
78:band gap
650:Bibcode
611:Bibcode
568:Bibcode
533:Bibcode
394:bismuth
358:bismuth
350:arsenic
275:silicon
266:(CuInSe
219:-vector
193:bismuth
185:arsenic
172:phonons
150:at the
708:Metals
676:
668:
586:
508:
471:
396:, and
374:carbon
136:metals
52:metals
674:S2CID
584:S2CID
506:S2CID
429:Metal
368:, an
306:metal
277:(Si))
176:holes
86:holes
48:white
44:black
666:PMID
469:ISBN
360:, α-
328:and
187:and
112:band
96:edit
72:and
58:the
54:and
658:doi
619:doi
576:doi
541:doi
498:doi
390:tin
372:of
362:tin
282:tin
694::
672:.
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656:.
646:13
644:.
640:.
617:.
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574:.
564:71
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270:))
144:eV
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103:A
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680:.
660::
652::
625:.
621::
613::
607:4
590:.
578::
570::
547:.
543::
535::
512:.
500::
494:8
477:.
268:2
234:2
217:k
66:F
63:E
42:(
23:.
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