Showing papers on "Band gap published in 2003"
TL;DR: In this paper, a comprehensive and up-to-date compilation of band parameters for all of the nitrogen-containing III-V semiconductors that have been investigated to date is presented.
Abstract: We present a comprehensive and up-to-date compilation of band parameters for all of the nitrogen-containing III–V semiconductors that have been investigated to date. The two main classes are: (1) “conventional” nitrides (wurtzite and zinc-blende GaN, InN, and AlN, along with their alloys) and (2) “dilute” nitrides (zinc-blende ternaries and quaternaries in which a relatively small fraction of N is added to a host III–V material, e.g., GaAsN and GaInAsN). As in our more general review of III–V semiconductor band parameters [I. Vurgaftman et al., J. Appl. Phys. 89, 5815 (2001)], complete and consistent parameter sets are recommended on the basis of a thorough and critical review of the existing literature. We tabulate the direct and indirect energy gaps, spin-orbit and crystal-field splittings, alloy bowing parameters, electron and hole effective masses, deformation potentials, elastic constants, piezoelectric and spontaneous polarization coefficients, as well as heterostructure band offsets. Temperature an...
2,525 citations
TL;DR: In this article, the authors proposed a transparent ZnO-based thin-film transistors (TFTs) for select-transistors in each pixel of an active-matrix liquid-crystal display.
Abstract: Highly transparent ZnO-based thin-film transistors (TFTs) are fabricated with optical transmission (including substrate) of ∼75% in the visible portion of the electromagnetic spectrum. Current–voltage measurements indicate n-channel, enhancement-mode TFT operation with excellent drain current saturation and a drain current on-to-off ratio of ∼107. Threshold voltages and channel mobilities of devices fabricated to date range from ∼10 to 20 V and ∼0.3 to 2.5 cm2/V s, respectively. Exposure to ambient light has little to no observable effect on the drain current. In contrast, exposure to intense ultraviolet radiation results in persistent photoconductivity, associated with the creation of electron-hole pairs by ultraviolet photons with energies greater than the ZnO band gap. Light sensitivity is reduced by decreasing the ZnO channel layer thickness. One attractive application for transparent TFTs involves their use as select-transistors in each pixel of an active-matrix liquid-crystal display.
1,415 citations
TL;DR: It is demonstrated that the spatial distribution of carriers can be controlled within the type-II quantum dots, which makes their properties strongly governed by the band offset of the comprising materials.
Abstract: Type-II band engineered quantum dots (CdTe/CdSe(core/shell) and CdSe/ZnTe(core/shell) heterostructures) are described. The optical properties of these type-II quantum dots are studied in parallel with their type-I counterparts. We demonstrate that the spatial distribution of carriers can be controlled within the type-II quantum dots, which makes their properties strongly governed by the band offset of the comprising materials. This allows access to optical transition energies that are not restricted to band gap energies. The type-II quantum dots reported here can emit at lower energies than the band gaps of comprising materials. The type-II emission can be tailored by the shell thickness as well as the core size. The enhanced control over carrier distribution afforded by these type-II materials may prove useful for many applications, such as photovoltaics and photoconduction devices.
1,259 citations
TL;DR: In this paper, a review focusing on promising candidate materials (such as GaN, GaP and ZnO) is presented, where the introduction of Mn into these and other materials under the right conditions is found to produce ferromagnetism near or above room temperature.
Abstract: Recent advances in the theory and experimental realization of ferromagnetic semiconductors give hope that a new generation of microelectronic devices based on the spin degree of freedom of the electron can be developed. This review focuses primarily on promising candidate materials (such as GaN, GaP and ZnO) in which there is already a technology base and a fairly good understanding of the basic electrical and optical properties. The introduction of Mn into these and other materials under the right conditions is found to produce ferromagnetism near or above room temperature. There are a number of other potential dopant ions that could be employed (such as Fe, Ni, Co, Cr) as suggested by theory [see, for example, Sato and Katayama-Yoshida, Jpn. J. Appl. Phys., Part 2 39, L555 (2000)]. Growth of these ferromagnetic materials by thin film techniques, such as molecular beam epitaxy or pulsed laser deposition, provides excellent control of the dopant concentration and the ability to grow single-phase layers. T...
968 citations
TL;DR: In this article, the conduction and valence band edges for electronic band gaps and Fermi levels are determined for Ta2O5, TaON, and Ta3N5 by ultraviolet photoelectron spectroscopy (UPS) and electrochemical analyses.
Abstract: The conduction and valence band edges for electronic band gaps and Fermi levels are determined for Ta2O5, TaON, and Ta3N5 by ultraviolet photoelectron spectroscopy (UPS) and electrochemical analyses. Reasonable agreement between the results of the two methods is obtained at the pH at which the ζ potentials of the particles are zero. The tops of the valence bands are found to be shifted to higher potential energies on the order Ta2O5 < TaON < Ta3N5, whereas the bottoms of the conduction bands are very similar in the range −0.3 to −0.5 V (vs NHE at pH = 0). From the results, it is concluded that TaON and Ta3N5 are promixing catalysts for the reduction and oxidation of water using visible light in the ranges λ < 520 nm and λ < 600 nm, respectively. It is also demonstrated that the proposed UPS technique is a reliable alternative to electrochemical analyses for determining the absolute band gap positions for materials in aqueous solutions that would otherwise be difficult to measure using electrochemical methods.
856 citations
TL;DR: In this article, X-ray diffraction and transmission electron microscopy were used to characterize the structural properties of anatase nano-drone nano-dioxide and showed a blue shift in the absorption edge of the diffuse reflectance ultraviolet spectrum.
788 citations
TL;DR: Theoretical work predicts that band gap changes can range between +/-100 meV per 1% stretch, depending on NT chirality, and the measurements here are consistent with this predicted range.
Abstract: We show that the band structure of a carbon nanotube (NT) can be dramatically altered by mechanical strain. We employ an atomic force microscope tip to simultaneously vary the NT strain and to electrostatically gate the tube. We show that strain can open a band gap in a metallic NT and modify the band gap in a semiconducting NT. Theoretical work predicts that band gap changes can range between � 100 meV per 1% stretch, depending on NT chirality, and our measurements are consistent with this predicted range.
646 citations
TL;DR: Ferromagnetism with T(C) > 350 K is observed in aggregated nanocrystals of Co(2+):ZnO that unambiguously demonstrates the existence of intrinsic high-T(C), ferromagnetsism in this class of DMSs.
Abstract: We report a method for the preparation of colloidal ZnO-diluted magnetic semiconductor quantum dots (DMS-QDs) by alkaline-activated hydrolysis and condensation of zinc acetate solutions in dimethyl sulfoxide (DMSO). Mechanistic studies reveal that Co2+ and Ni2+ dopants inhibit nucleation and growth of ZnO nanocrystals. In particular, dopants are quantitatively excluded from the critical nuclei but are incorporated nearly isotropically during subsequent growth of the nanocrystals. The smaller nanocrystal diameters that result upon doping are explained by the Gibbs−Thompson relationship between lattice strain and crystal solubility. We describe methods for cleaning the nanocrystal surfaces of exposed dopants and for redispersion of the final DMS-QDs. Homogeneous substitutional doping is verified by high-resolution low-temperature electronic absorption and magnetic circular dichroism (MCD) spectroscopies. A “giant Zeeman effect” is observed in the band gap transition of Co2+:ZnO DMS-QDs. MCD and Zeeman spect...
621 citations
TL;DR: In this paper, the optical and electronic properties of the In1−xGaxN alloys have been investigated and shown to exhibit a much higher resistance to high energy (2 MeV) proton irradiation than the standard currently used photovoltaic materials such as GaAs and GaInP, and therefore offer great potential for radiation-hard high-efficiency solar cells for space applications.
Abstract: High-efficiency multijunction or tandem solar cells based on group III–V semiconductor alloys are applied in a rapidly expanding range of space and terrestrial programs. Resistance to high-energy radiation damage is an essential feature of such cells as they power most satellites, including those used for communications, defense, and scientific research. Recently we have shown that the energy gap of In1−xGaxN alloys potentially can be continuously varied from 0.7 to 3.4 eV, providing a full-solar-spectrum material system for multijunction solar cells. We find that the optical and electronic properties of these alloys exhibit a much higher resistance to high-energy (2 MeV) proton irradiation than the standard currently used photovoltaic materials such as GaAs and GaInP, and therefore offer great potential for radiation-hard high-efficiency solar cells for space applications. The observed insensitivity of the semiconductor characteristics to the radiation damage is explained by the location of the band edge...
598 citations
TL;DR: In this article, the authors show how topology optimization can be used to design and optimize periodic materials and structures exhibiting phononic band gaps, which can prevent elastic waves in certain frequency ranges from propagating.
Abstract: Phononic band-gap materials prevent elastic waves in certain frequency ranges from propagating, and they may therefore be used to generate frequency filters, as beam splitters, as sound or vibration protection devices, or as waveguides. In this work we show how topology optimization can be used to design and optimize periodic materials and structures exhibiting phononic band gaps. Firstly, we optimize infinitely periodic band-gap materials by maximizing the relative size of the band gaps. Then, finite structures subjected to periodic loading are optimized in order to either minimize the structural response along boundaries (wave damping) or maximize the response at certain boundary locations (waveguiding).
586 citations
TL;DR: In this article, high-spatial-frequency periodic structures on the surfaces of InP, GaP, and GaAs have been observed after multiple-pulse femtosecond laser irradiation at wavelengths in the transparency regions of the respective solids.
Abstract: High-spatial-frequency periodic structures on the surfaces of InP, GaP, and GaAs have been observed after multiple-pulse femtosecond laser irradiation at wavelengths in the transparency regions of the respective solids. The periods of the structures are substantially shorter than the wavelengths of the incident laser fields in the bulk materials. In contrast, high-frequency structures were not observed for laser photon energies above the band gaps of the target materials.
TL;DR: Layered heterostructures combining ordinary and negative refractive index materials are shown to display a new type of photonic band gap corresponding to zero (volume) averaged refractiveIndex, distinct from band gaps induced by Bragg scattering.
Abstract: Layered heterostructures combining ordinary and negative refractive index materials are shown to display a new type of photonic band gap corresponding to zero (volume) averaged refractive index. Distinct from band gaps induced by Bragg scattering, the zero-$\overline{n}$ gap is invariant upon a change of scale length and is insensitive to disorder that is symmetric in the random variable. A metallic structure that exhibits such a band gap is explicitly designed, and its properties are calculated with accurate finite difference time domain simulations.
TL;DR: In this article, the effects of stacking behavior of hexagonal basal layers to the structural stability and electronic properties of h-BN were investigated thoroughly using first-principles calculations based on the density-functional theory local density approximation.
Abstract: Effects of stacking behavior of hexagonal basal layers to the structural stability and electronic properties of h-BN were investigated thoroughly using first-principles calculations based on the density-functional theory local-density approximation. Three of five possible h-BN structures with ``good'' stacking were found to be stable or substable. Considering that intrinsic stacking fault exist in real h-BN crystals which results in mixed stacking behavior, the experimentally observed large interlayer spacing of structures with stacking disorder such as PBN and t-BN can be understood. A substable structure with a direct band gap of about 3.395 eV was predicted. The existence of this substable structure and related intrinsic stacking fault in real h-BN explains the discrepancy in the nature of the band gap and the large variation in the observed band-gap values of h-BN.
TL;DR: The optical absorption coefficient of the sputtered Cu 2 ZnSnS 4 thin films was less than that of CuInS 2 thin film, however, the band gap energy was more appropriate for photovoltaic materials.
TL;DR: In this article, the authors derived new expressions for specific on-resistance in power semiconductor devices, such as heterojunction MOSFETs, using GaN and compared these new expressions to the previous literature.
Abstract: An advantage for some wide bandgap materials, that is often overlooked, is that the thermal coefficient of expansion (CTE) is better matched to the ceramics in use for packaging technology. It is shown that the optimal choice for uni-polar devices is clearly GaN. It is further shown that the future optimal choice for bipolar devices is C (diamond) owing to the large bandgap, high thermal conductivity, and large electron and hole mobilities. A new expression relating the critical electric field for breakdown in abrupt junctions to the material bandgap energy is derived and is further used to derive new expressions for specific on-resistance in power semiconductor devices. These new expressions are compared to the previous literature and the efficacy of specific power devices, such as heterojunction MOSFETs, using GaN are discussed.
TL;DR: This review highlights the recent developments in the area of donor-acceptor type low band gap polymers with special emphasis on polysquaraines, due to their unique optical properties.
Abstract: In recent years, considerable effort has been directed towards the synthesis of conjugated polymers with low optical band gaps (Eg), since they show intrinsic electrical conductivity. One of the approaches towards the designing of such polymers is the use of strong donor and acceptor monomers at regular arrangements in the repeating units, which has limited success in many cases. An alternate strategy is the use of organic dyes, having inherently low HUMO–LUMO separation, as building blocks. Extension of conjugation in organic dyes is therefore expected to result in oligomers and polymers with near infrared absorption, which is a signature of low band gaps. Squaraine dyes are ideal candidates for this purpose due to their unique optical properties. This review highlights the recent developments in the area of donor–acceptor type low band gap polymers with special emphasis on polysquaraines.
TL;DR: The steady-state photoluminescence (PL) properties of cadmium selenide quantum dots (QDs) with a zinc sulfide overlayer [(CdSe)ZnS] can be strongly dependent on temperature in the range from 100 to 315 K as discussed by the authors.
Abstract: The steady-state photoluminescence (PL) properties of cadmium selenide quantum dots (QDs) with a zinc sulfide overlayer [(CdSe)ZnS] can be strongly dependent on temperature in the range from 100 to 315 K. The PL intensity from 50 to 55 A (CdSe)ZnS QDs in poly(lauryl methacrylate) matrices increases by a factor of ∼5 when the temperature is decreased from 315 to 100 K, and the peak of the emission band is blueshifted by 20 nm over the same range. The change in PL intensity is appreciable, linear, and reversible (−1.3% per °C) for temperatures close to ambient conditions. These properties of (CdSe)ZnS dots are retained in a variety of matrices including polymer and sol–gel films, and they are independent of excitation wavelength above the band gap. The significant temperature dependence of the luminescence combined with its insensitivity to oxygen quenching establishes (CdSe)ZnS dots as optical temperature indicators for temperature-sensitive coatings.
TL;DR: In this article, a tensile strain induced band gap shrinkage is shown for Ge-on-Si pin diodes, which is attributed to the difference of thermal expansion between Ge and Si.
Abstract: Band gap shrinkage induced by tensile strain is shown for Ge directly grown on Si substrate. In Ge-on-Si pin diodes, photons having energy lower than the direct band gap of bulk Ge were efficiently detected. According to photoreflectance measurement, this property is due to band gap shrinkage. The origin of the shrinkage is not the Franz–Keldysh effect but rather tensile strain. It is discussed that the generation of such a tensile strain can be ascribed to the difference of thermal expansion between Ge and Si. Advantages of this tensile Ge for application to photodiode are also discussed.
TL;DR: In this article, a three-dimensional tungsten photonic crystal is realized with a complete photonic band gap at wavelengths λ⩾3 μm, and an optical-to-electric conversion efficiency of ∼34% and electrical power of ∼14 W/cm2 is theoretically possible.
Abstract: A three-dimensional tungsten photonic crystal is experimentally realized with a complete photonic band gap at wavelengths λ⩾3 μm. At an effective temperature of 〈T〉∼1535 K, the photonic crystal exhibits a sharp emission at λ∼1.5 μm and is promising for thermal photovoltaic (TPV) power generation. Based on the spectral radiance, a proper length scaling and a planar TPV model calculation, an optical-to-electric conversion efficiency of ∼34% and electrical power of ∼14 W/cm2 is theoretically possible.
TL;DR: In this paper, a detailed study of RF-MBE growth conditions for obtaining high-quality InN films is presented, showing that the fundamental band gap of InN is about 0.8 eV.
Abstract: The fundamental band gap of InN has been thought to be about 1.9 eV for a long time. Recent developments of metalorganic vapor phase epitaxy (MOVPE) and RF-molecular beam epitaxy (RF-MBE) growth technologies have made it possible to obtain high-quality InN films. A lot of experimental results have been presented very recently, suggesting that the true band-gap energy of InN should be less than 1.0 eV. In this paper, we review the results of the detailed study of RF-MBE growth conditions for obtaining high-quality InN films. The full widths at half maximum (FWHMs) of ω-mode X-ray diffraction (XRD), ω–2θ mode XRD and E2 (high-frequency)-phonon-mode peaks in the Raman scattering spectrum of the grown layer were 236.7 arcsec, 28.9 arcsec and 3.7 cm-1, respectively. The carrier concentration and room temperature electron mobility were 4.9×1018 cm-3 and 1130 cm2/Vs, respectively. Photoluminescence and optical absorption measurements of these high-quality InN films have clearly demonstrated that the fundamental band gap of InN is about 0.8 eV. Studies on the growth and characterization of InGaN alloys over the entire alloy composition further supported that the fundamental band gap of InN is about 0.8 eV.
TL;DR: In this article, the band gap of GaAsBi epitaxial layers as a function of bismuth concentration up to 3.6% was determined using modulated electroreflectance.
Abstract: The band gap of GaAsBi epitaxial layers as a function of bismuth concentration up to 3.6% is determined. The optical transitions were measured by modulated electroreflectance. The energy of the band gap decreases at a linearized rate of 88 meV/% Bi, or 83 meV/% Bi for the heavy hole to conduction band transition for GaAsBi strained to GaAs. The valence-band splitting increases faster than that of GaAs under similar compressive strain whereas the temperature dependence of the observed GaAsBi transitions is similar to that of GaAs.
TL;DR: In this paper, the fundamental band gap of InN films grown by molecular beam epitaxy have been measured by transmission and photoluminescence spectroscopy as a function of temperature.
Abstract: The fundamental band gap of InN films grown by molecular beam epitaxy have been measured by transmission and photoluminescence spectroscopy as a function of temperature The band edge absorption energy and its temperature dependence depend on the doping level The band gap variation and Varshni parameters of InN are compared with other group III nitrides The energy of the photoluminescence peak is affected by the emission from localized states and cannot be used to determine the band gap energy Based on the results obtained on two samples with distinctly different electron concentrations, the effect of degenerate doping on the optical properties of InN is discussed
TL;DR: The recent progress at Sony in the design of practical olivine-type cathodes is reviewed briefly in this article, where the lattice frustration induced by the strong electron (Mn 3+ : 3d 4 −e g σ ∗ )-lattice interaction (Jahn-Teller effect) in the charged state of Li(Mn y Fe 1− y )PO 4 (0≤ y ≤ 1).
TL;DR: Growth of indium phosphide (InP) quantum wires having diameters in the strong-confinement regime are reported and a comparison of their bandgaps with those previously reported for InP quantum dots are compared.
Abstract: The size dependence of the bandgap is the most identifiable aspect of quantum confinement in semiconductors; the bandgap increases as the nanostructure size decreases. The bandgaps in one-dimensional (1D)-confined wells, 2D-confined wires, and 3D-confined dots should evolve differently with size as a result of the differing dimensionality of confinement. However, no systematic experimental comparisons of analogous 1D, 2D or 3D confinement systems have been made. Here we report growth of indium phosphide (InP) quantum wires having diameters in the strong-confinement regime, and a comparison of their bandgaps with those previously reported for InP quantum dots. We provide theoretical evidence to establish that the quantum confinement observed in the InP wires is weakened to the expected extent, relative to that in InP dots, by the loss of one confinement dimension. Quantum wires sometimes behave as strings of quantum dots, and we propose an analysis to generally distinguish quantum-wire from quantum-dot behaviour.
TL;DR: This work reports on a general method for the growth of soluble nanorods applied to semiconductors with the zinc-blende cubic lattice structure, and provides an unexpected link between two successful strategies for growing high-quality nanomaterials, the vapour–liquid–solid approach for growing nanowires and the colloidal approach for synthesizing soluble nanocrystals.
Abstract: Dimensionality and size are two factors that govern the properties of semiconductor nanostructures1,2. In nanocrystals, dimensionality is manifested by the control of shape, which presents a key challenge for synthesis3,4,5. So far, the growth of rod-shaped nanocrystals using a surfactant-controlled growth mode, has been limited to semiconductors with wurtzite crystal structures, such as CdSe (ref. 3). Here, we report on a general method for the growth of soluble nanorods applied to semiconductors with the zinc-blende cubic lattice structure. InAs quantum rods with controlled lengths and diameters were synthesized using the solution–liquid–solid mechanism6 with gold nanocrystals as catalysts7. This provides an unexpected link between two successful strategies for growing high-quality nanomaterials, the vapour–liquid–solid approach for growing nanowires8,9,10,11,12, and the colloidal approach for synthesizing soluble nanocrystals13,14,15. The rods exhibit both length- and shape-dependent optical properties, manifested in a red-shift of the bandgap with increased length, and in the observation of polarized emission covering the near-infrared spectral range relevant for telecommunications devices16,17.
TL;DR: Theoretical investigations of doping of several wide-gap materials suggest a number of rather general, practical "doping principles" that may help guide experimental strategies for overcoming doping bottlenecks as discussed by the authors.
Abstract: Theoretical investigations of doping of several wide-gap materials suggest a number of rather general, practical “doping principles” that may help guide experimental strategies for overcoming doping bottlenecks.
TL;DR: In this paper, the electronic energy band structure, density of states (DOS) and charge density contour of KNbO3 in the paraelectric cubic phase have been studied using the full-potential linearized augmented plane wave method within the generalized gradient approximation for exchange and correlation.
Abstract: The electronic energy band structure, density of states (DOS) and charge density contour of KNbO3 in the paraelectric cubic phase have been studied using the full-potential linearized augmented plane wave method within the generalized gradient approximation for exchange and correlation. The band structure shows an indirect (R–Γ) band gap. From the DOS analysis as well as charge density studies, we find that the bonding between K and NbO3 is mainly ionic while that between Nb and O is covalent. We have also reported results on the pressure variation of the energy gap of this compound and found that the band gap increases with increasing pressure. In order to understand the optical properties of the perovskite, the real and imaginary parts of the dielectric function, reflectivity, absorption coefficient, optical conductivity, electron energy-loss function, refractive index and extinction coefficient were calculated. The general profiles of the optical spectra were analysed and origins of the structures discussed.
TL;DR: In this paper, the vibrational response of finite periodic lattice structures subjected to periodic loading is investigated, and the effects of boundaries, viscous damping, and imperfections are studied by analyzing two examples; a 1-D filter and a 2-D wave guide.
TL;DR: In this paper, the relationship between composition, crystal structure and the electronic structure of oxides containing octahedrally coordinated d0 transition metal ions was quantitatively investigated using linear muffin tin orbital methods and UV-visible diffuse reflectance spectroscopy, respectively.
TL;DR: It is shown that the opening of the band gap in semiconducting carbon nanotubes determines the nonlinear response dynamics over the whole visible and near-infrared spectrum.
Abstract: Time-resolved carrier dynamics in single-wall carbon nanotubes is investigated by means of two-color pump-probe experiments. The recombination dynamics is monitored by probing the transient photobleaching observed on the interband transitions of the semiconducting tubes. This dynamics takes place on a 1 ps time scale which is 1 order of magnitude slower than in graphite. Transient photoinduced absorption is observed for nonresonant probing and is interpreted as a global redshift of the pi-plasmon resonance. We show that the opening of the band gap in semiconducting carbon nanotubes determines the nonlinear response dynamics over the whole visible and near-infrared spectrum.