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Topic: Direct bandgap

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	Optoelectronic devices
		Direct bandgap semiconductors, i.e semiconductors for which the minimum of the conduction band occurs at the same wavevector, k, as the maximum of the valence band, have a stronger absorption of light as characterized by a larger absorption coefficient.
		E-k diagram illustrating a) Photon absorption in a direct bandgap semiconductor b) Photon absorption in an indirect bandgap semiconductor assisted by phonon absorption and c) Photon absorption in an indirect bandgap semiconductor assisted by phonon emission.
		For an indirect bandgap semiconductor, the conduction band is not vertically aligned to the valence band as shown in Figure 4.6.1(b).
	ece-www.colorado.edu /~bart/book/book/chapter4/ch4_6.htm (2349 words)

	Direct bandgap
		In semiconductor physics, a direct bandgap means that the conduction band lies directly above the valence band, in momentum space (see E-k plots[?]).
		The prime example of a direct bandgap semiconductor is gallium arsenide - a material commonly used in laser diodes.
		See indirect bandgap for an explanation of the connection between bandgap offset and light emission.
	www.fastload.org /di/Direct_bandgap.html (116 words)

	Reflectance method to determine and control the temperature of thin layers or wafers and their surfaces with special ...
		Due to the relationship between direct bandgap and optical absorption coefficient.alpha., analysis of the reflected optical radiation will provide an indication of the direct bandgap of the material which, in turn, is indicative of the material's temperature.
		The property of the material on which this invention is based is the dependence of the bandgap on temperature, and the dependence of the optical absorption coefficient,.alpha., of light of a given energy on the difference between the latter and the bandgap energy (which must be smaller than the light energy).
		The figure shows the change in the direct bandgap of a semiconductor as a function of temperature (the example is a semiconductor, such as GaAs, whose direct bandgap decreases as the temperature increases).
	www.freepatentsonline.com /5098199.html (3713 words)

	Direct bandgap
		In semiconductor physics, a direct bandgap means that the conduction band lies directly above the valence band, in momentum space (see E-k plots[?]).
		The prime example of a direct bandgap semiconductor is gallium arsenide - a material commonly used in laser diodes.
		See indirect bandgap for an explanation of the connection between bandgap offset and light emission.
	www.ebroadcast.com.au /lookup/encyclopedia/di/Direct_bandgap.html (77 words)

	On the horizon: a virtually perfect solar cell
		The low bandgap of indium nitride suggests that by simply varying proportions of indium and gallium, it may be possible to create rugged, inexpensive devices that can convert the full spectrum of sunlight to electric current.
		A semiconductor's bandgap is not a physical space; rather it is the difference between the energy of the electrons in its filled valence band and the energy electrons would need to occupy its empty conduction band.
		That's because silicon is an "indirect bandgap " semiconductor, in which creation of an electron-hole pair requires participation of the crystal lattice vibrations, wasting a lot of an incoming photon's energy.
	enews.lbl.gov /Science-Articles/Archive/MSD-perfect-solar-cell.html (672 words)

	Direct bandgap (Site not responding. Last check: )
		This is 'radiative recombination', See indirect bandgap for an explanation of the connection between bandgap offset crystalline silicon, the momentum of the conduction band minimum and valence light emission from indirect semiconductors is very inefficient and weak.
		The prime example of a direct bandgap semiconductor is gallium arsenide - a conduction band lies directly above the maximum of the valence band maximum, while not conserve momentum and is forbidden.
		The prime example of a direct bandgap semiconductor is gallium arsenide - a conduction band lies directly above the maximum of the valence band in momentum In semiconductor physics, a direct bandgap semiconductor, electrons at the conduction-band and light emission.
	communications.boekebeurs.be /Directbandgap (356 words)

	Ragan, Regina (2002-01-16) Direct energy bandgap group IV alloys and nanostructures. ...
		Deformation potential theory calculations were performed to predict the effect of coherency strain on the extrema points of the conduction band and the valence band.
		Coherency strain did not change the SnxGe1-x energy bandgap when the strain axis was along [001] but deformation potential theory predicted the absence of an indirect to direct energy bandgap transition when the strain axis was along [111].
		A high degree of tunability of the bandgap energy with the quantum dot radius is expected for a-Sn.
	etd.caltech.edu /etd/available/etd-02142002-211940 (483 words)

	Question About Indirect vs. Direct Bandgap Semiconductors
		If the emitted wavelengths have a different frequency than the impinging wavelengths, then there the bandgap must be indirect because some of the added energy would have to be converted to phonon energy in order for an emission to take place.
		Well, a direct bandgap has a conductance band minima and a valence band maxima at the same wavevector.
		P.S. Direct bandgap semiconductors are sometimes reffered to as "optically active" and indirect as "optically inactive".
	www.physicsforums.com /showthread.php?t=2141 (355 words)

	Bandgap energy, - band gap
		The average bandgap energy of AlN and GaN is determined to be 5.62 ± 0.35 and 3.87 ± 0.36 eV, respectively.
		BANDGAP ENERGY (Eg) The energy difference between the bottom of the conduction band and the top of the valence band in a semiconductor or an insulator.
		A threshold filter method is applied to estimate the average value and SD of the bandgap energy from barrier and well regions in the energy map.
	xn--ekr44gr47awri.com /?q=bandgap-energy (1282 words)

	Spartanburg SC \| GoUpstate.com \| Spartanburg Herald-Journal
		In a direct bandgap semiconductor, electrons at the conduction-band minimum can combine directly with holes at the valence band maximum, while conserving momentum.
		The energy of the recombination across the bandgap will be emitted in the form of a photon of light.
		Recombination occurs with the mediation of a third body, such as a phonon or a crystallographic defect, which allows for conservation of momentum.
	www.goupstate.com /apps/pbcs.dll/section?category=NEWS&template=wiki&text=direct_bandgap (229 words)

	direct energy \| Energy Consulting
		Direct Bandgap Energy Calculator InAsxSb1-x, Direct Energy Gap: Lattice Constant: Density: Equations used to calculate Direct Energy Gap
		Direct Energy Services applied for a license on Nov. 18, 2004, showing its compliance with Direct Energy Services LLC is headquartered in Dublin, Ohio.
		Direct Energy Victims under Heavy Attack : NC Indymedia
	www.oilgasmeter.co.uk /direct_energy.html (326 words)

	Optical Detector
		In this context direct and indirect absorption may be contrasted with direct and indirect emission Therefore as may be seen from Fig.
		The bandgap for direct absorption in silicon is 4.10 eV corresponding to a threshold of 0.30
		These materials are potentially superior to germanium because their bandgaps can be tailored to the desired wavelength by changing the relative concentrations of their constituents, resulting in lower dark currents.
	members.tripod.com /optic1999/chapter6.htm (5693 words)

	Home
		In a directly bandgap material, it is efficient to have direct recombination of electron-hole pair without involving 3rd party particles (e.g.
		And a photon (f=Eg/h, where f is the frequency of the photon, Eg is the bandgap of the material and h is the Planck constant) is then emitted.
		Since the photon has the same energy as the bandgap, there is a large chance that it will be re-absorbed before the can escape from the semiconductor and contribute to the light of the LED.
	www.kodkodkod.com /files/led.htm (269 words)

	Blue Diode Research Hastens Day of Large-Scale Solid-State Light Sources
		In the 1950s it was discovered that all the direct bandgap semiconductors combine one or more elements from group III of the periodic table, such as gallium, with one or more from group V, such as arsenic.
		LEDs made from gallium arsenide and its alloys became available in the 1960s, but the direct bandgaps of conventional group III-V semiconductors covered only the spectral range from red to amber, leaving much of the visible spectrum beyond the reach of LEDs.
		A different problem in the manufacture of LEDs made with gallium nitride is that large cracks develop in gallium nitride films doped with silicon, which is used for the n-type base structure of the devices.
	www.lbl.gov /Science-Articles/Archive/blue-light-diodes.html (1433 words)

	Computational design of direct-bandgap semiconductors that lattice-match silicon : Abstract : Nature
		Here we propose a more direct solution to integrating silicon electronics with optical components.
		We have computationally designed two hypothetical direct-bandgap semiconductor alloys, the synthesis of which should be possible through the deposition of specific group-IV precursor molecules
		The calculated bandgaps (and hence the frequency of emitted light) lie in the window of minimal absorption in current optical fibres.
	www.nature.com /doifinder/10.1038/35051054 (279 words)

	WideBandGap Optronix Laboratory
		III-Nitride material systems have a variety of applications ranging from high brightness LEDs for general lighting, lasers for high density optical storage systems, UV emitters for homeland security applications such as biological agent detection and water purification, to high power RF transistors for cell phone and satellite communication, switching applications and harsh environment sensors.
		N, 0semiconductors that have certain unique properties as compared to the conventional semiconductors such as Si and GaAs.
		The enabling properties are the wide band gap of the material system and bandgap engineering (adjustable from 0.9 eV for InN to 3.4eV for GaN to 6.2 eV for AlN) as well as its direct bandgap.
	www.albany.edu /WBGOptronixlab (186 words)

	Semiconductor Materials For Electronics and Chip Industry: Quick Chemistry Facts
		Semiconductors that have an indirect bandgap are inefficient at emitting light.
		Semiconductors that have an direct bandgap are good light emitters.
		A narrow bandgap semiconductor is a semiconductor with an energy bandgap narrower than about 2 eV suitable for tunnel devices and infrared technology.
	www.chemistry.patent-invent.com /chemistry/semiconductor_materials.html (356 words)

	IEEE Spectrum: Light From Silicon
		Because energy is always conserved, this recombination of an electron and a hole is accompanied by the emission of a particle, preferably a photon, whose energy matches the difference between the conduction band and the valence band—the bandgap energy.
		In direct-bandgap semiconductors, such as gallium arsenide, it happens that the maximum energy in the valence band and the minimum energy in the conduction band occur at the same value of electron momentum.
		The other idea scientists have pursued is to sidestep silicon's bandgap problems by having another material, embedded within the silicon device, emit the light.
	www.spectrum.ieee.org /print/1886 (3114 words)

	-MRS-
		The electronic structure and dynamical processes of indirect bandgap semiconductor quantum dots (QDs) are interesting due to the complexity of the physics, the difficulty in obtaining useful experimental results, and the increasing interest in technological applications.
		Unlike direct bandgap QDs, steady-state linear optical spectroscopy reveals little useful information due in part to the indirect nature of the lowest optical transition of the bulk material.
		As are of particular interest since the larger bandgap of Al containing compounds allow the wavelength of emission to be tuned from the visible to the infra-red by simply controlling the size of the islands.
	lucy.mrs.org /meetings/spring99/abstractbook/AbstractBookW.html (18309 words)

	Pressure Dependence
		Recently InN was found to have a narrow fundamental bandgap of 0.7 eV [1-3] instead of the previously believed 1.9 eV.
		When a hydrostatic pressure is applied to a direct-bandgap semiconductor, the interatomic distance decrease, and the direct bandgap usually increases.
		The hydrostatic pressure dependence of the fundamental bandgap is studied by the blue shifts of the optical absorption edge in a diamond anvil cell (Figure 1).
	www.mse.berkeley.edu /~xli/SLi_Homepage/P_dep.htm (681 words)

	Brown Technology Partnerships: Indirect-Bandgap Semiconductor Laser and Method to Fabricate Same
		Some of these efforts are directed towards enhancing silicon light emission and attempt to achieve this goal via doping or improved external coupling of the emitted photons, or defect-states or surface recombination, or quantum-confinement effects.
		Porous silicon is one well-known example of this prior research, wherein a large surface-to-volume ratio and/or highly emissive surface states are created by severe chemical impregnation and material modification of the surface layer.
		The layer of semiconductor material may be direct bandgap or an indirect-bandgap semiconductor material.
	research.brown.edu /btp/technologies_detail.php?id=1138649348 (662 words)

	[No title]
		Indicate if it is a direct band gap or an indirect band gap.
		What physical significance or consequence does the direct or indirect bandgap have (i.e., in terms of the light emission efficiency) ?
		Would the Light Emitting Diodes and Laser Diodes be made from a direct bandgap materials or from the indrect bandgap materials ?
	jas.eng.buffalo.edu /education/semicon/AlGaAs/worksheet.html (89 words)

	Library
		The waveguide arrays are fabricated by titanium in-diffusion in a photorefractive copper-doped lithium niobate crystal, and the optical nonlinearity arises from the bulk photovoltaic effect.
		A 12, 1087 (1995)] for one-dimensional (1D) diffraction gratings is used for the modeling of diffraction properties of photonic bandgap (PBG) structures.
		We present a fast Hankel transform (FHTn) method for direct numerical evaluation of electromagnetic (EM) field propagation through an axially symmetric system.
	r6u.net /diffractive-diffraction-diffractive/diffractive-diffraction-diffractive-10.php (1248 words)

	Laser Focus World - PHOTONIC FRONTIERS: SILICON PHOTONICS - Closing in on silicon lasers
		Silicon crystals have an indirect bandgap structure that makes it difficult for electrons in the conduction band to drop into holes in the valence band and emit light efficiently.
		In indirect bandgap materials such as silicon, conduction-band electrons have to change their momentum to drop to the valence band (see Fig.
		Silicon with a nanopattern etched in the surface emits a directional beam from the edge.
	lfw.pennnet.com /Articles/Article_Display.cfm?Section=ARTCL&ARTICLE_ID=248133&VERSION_NUM=2&p=12 (1520 words)

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