Showing papers on "Band gap published in 1997"
TL;DR: In this paper, the authors describe a strategy for identifying oxide materials that should combine p-type conductivity with good optical transparency, and illustrate the potential of this approach by reporting the properties of thin films of CuAlO2, a transparent oxide having room-temperature p- type conductivity up to 1'S'cm−1.
Abstract: Optically transparent oxides tend to be electrical insulators, by virtue of their large electronic bandgap (⩾3.1 eV). The most notable exceptions are doped versions of the oxides In2O3, SnO2 and ZnO—all n-type (electron) conductors—which are widely used as the transparent electrodes in flat-panel displays1,2. On the other hand, no transparent oxide exhibiting high p-type (hole) conductivity is known to exist, whereas such materials could open the way to a range of novel applications. For example, a combination of the two types of transparent conductor in the form of a pn junction could lead to a ‘functional’ window that transmits visible light yet generates electricity in response to the absorption of ultraviolet photons. Here we describe a strategy for identifying oxide materials that should combine p-type conductivity with good optical transparency. We illustrate the potential of this approach by reporting the properties of thin films of CuAlO2, a transparent oxide having room-temperature p-type conductivity up to 1 S cm−1. Although the conductivity of our candidate material is significantly lower than that observed for the best n-type conducting oxides, it is sufficient for some applications, and demonstrates that the development of transparent p-type conductors is not an insurmountable goal.
1,871 citations
TL;DR: In this paper, the absorption coefficient for a 0.4-μm-thick GaN layer grown on a polished sapphire substrate was determined from transmission measurements at room temperature.
Abstract: The absorption coefficient for a 0.4-μm-thick GaN layer grown on a polished sapphire substrate was determined from transmission measurements at room temperature. A strong, well defined exciton peak for the A and B excitons was obtained. The A, B, and C excitonic features are clearly defined at 77 K. At room temperature, an energy gap Eg=3.452±0.001 eV and an exciton binding energy ExA,B=20.4±0.5 meV for the A and B excitons and ExC=23.5±0.5 meV for the C exciton were determined by analysis of the absorption coefficient. From this measured absorption coefficient, together with the detailed balance approach of van Roosbroek and Shockley, the radiative constant B=1.1×10−8 cm3/s was obtained.
665 citations
TL;DR: In this paper, the authors studied the dependence of the absorption edge and the refractive index of wurtzite AlxGa1−xN films on temperature and composition using transmission and photothermal deflection spectroscopy.
Abstract: We have studied the dependence of the absorption edge and the refractive index of wurtzite AlxGa1−xN films on temperature and composition using transmission and photothermal deflection spectroscopy. The Al molar fraction of the AlxGa1−xN films grown by plasma induced molecular beam epitaxy was varied through the entire range of composition (0⩽x⩽1). We determined the absorption edges of AlxGa1−xN films and a bowing parameter of 1.3±0.2 eV. The refractive index in the photon energy range between 1 and 5.5 eV and temperatures between 7 and 295 K was deduced from the interference fringes. The static refractive index n(0) changed from 2.29 for GaN to 1.96 for AlN at room temperature. A variation of temperature from 295 to 7 K resulted in a decrease of refractive index (at photon energies close to the band gap) by 0.05±0.01 and in an energy shift of the absorption edge of about 64±5 meV independent of the Al content of the films. Using the Kramers–Kronig dispersion relation and an approximation for the dispersion coefficient for photon energies near the band gap, the refractive index could be described as a function of photon energy, Al content, and temperature.
576 citations
TL;DR: In this article, the Coulomb interaction gives rise to several exciton bound states as well as an increase of the energy gap in carbon nanotubes (CN) and the exciton energy is shifted to higher energy side than the unperturbed band gap because the effect on the band gap is larger.
Abstract: Exciton energy levels and corresponding optical spectra are calculated in carbon nanotubes (CN) in the conventional screened Hartree-Fock approximation within a k · p scheme. The Coulomb interaction gives rise to several exciton bound states as well as the increase of the energy gap. The exciton energy is shifted to higher energy side than the unperturbed band gap because the effect on the band gap is larger. The considerable amount of the optical intensity is transferred to exciton bound states because of the one-dimensional nature of CN's.
569 citations
TL;DR: In this paper, the structural, electrical, and optical properties of aluminum doped zinc oxide (AZO) films are investigated in terms of the preparation conditions, such as the Al2O3 content in the target, rf power, substrate temperature and working pressure.
Abstract: Aluminum doped zinc oxide (AZO) films are prepared by rf magnetron sputtering on glass or Si substrates using specifically designed ZnO targets containing different amount of Al2O3 powder as the Al doping source. The structural, electrical, and optical properties of the AZO films are investigated in terms of the preparation conditions, such as the Al2O3 content in the target, rf power, substrate temperature and working pressure. The crystal structure of the AZO films is hexagonal wurtzite. The orientation, regardless of the Al content, is along the c axis perpendicular to the substrate. The doping concentration in the film is 1.9 at. % for 1 wt % Al2O3 target, 4.0 at. % for 3 wt % Al2O3 target, and 6.2 at. % for 5 wt % Al2O3 target. The resistivity of the AZO film prepared with the 3 wt % Al2O3 target is ∼4.7×10−4 Ω cm, and depends mainly on the carrier concentration. The optical transmittance of a 1500-A-thick film at 550 nm is ∼90%. The optical band gap depends on the Al doping level and on the microstr...
563 citations
TL;DR: In this article, the X-ray diffraction pattern of CZTS thin films showed that these films had a stannite structure, and the optical band gap energy was estimated as 1.45 eV.
481 citations
TL;DR: A recent review of progress in plastic photonic devices fabricated with semiconducting polymers can be found in this article, where conjugated polymers have been used to construct high-performance polymers of different colors.
Abstract: I. Semiconducting Polymers as Materials for “Plastic” Photonics Devices Solid-state photonic devices are a class of devices in which the quantum of light, the photon, plays a role. Because the interband optical transition (absorption and/or emission) is involved in photonic phenomena and because photon energies from near-infrared to near-ultraviolet are of interest, the relevant materials are semiconductors with band gaps in the range from 1 to 3 eV. Typical inorganic semiconductors used for photonic devices are Si, Ge, and Group III-V and Group II-VI alloys.1 Conjugated polymers are a novel class of semiconductors that combine the optical and electronic properties of semiconductors with the processing advantages and mechanical properties of polymers. Important examples of polymers within this class include poly(p-phenylenevinylene) (PPV), poly(p-phenylene) (PPP), and polyfluorene (PF) derivatives whose molecular structures are shown in Figure 1. The relative simplicity with which high photoluminescence (PL) efficiency polymers of different colors can be achieved is in stark contrast to inorganic semiconductors, where, for example, bright blue light emitting diodes (LEDs) were not available until recently because of the difficulties in growing InGaN films.2 Most of the photonic phenomena known in conventional inorganic semiconductors have been observed in these semiconducting polymers. The dream of using such materials in high-performance “plastic” photonic devices is rapidly becoming reality: high-performance photonic devices fabricated from conjugated polymers have been demonstrated, including diodes,3 light-emitting diodes,4 photodiodes,5 field-effect transistors,6 polymer grid triodes,7 light-emitting electrochemical cells,8 and optocouplers,9 i.e., all the categories that characterize the field of photonic devices. These polymer-based devices have reached performance levels comparable to or even better than those of their inorganic counterparts. For a recent review of progress in plastic photonic devices fabricated with semiconducting polymers, see ref 10.
458 citations
TL;DR: In this paper, the authors employed the plane-wave pseudopotential method to study point defect complexes in GaN and AlN and found that defect complexes consisting of dominant donors bound to cation vacancies are likely to be formed in both materials.
Abstract: We have employed the plane-wave pseudopotential method to study point defect complexes in GaN and AlN. The results reveal that defect complexes consisting of dominant donors bound to cation vacancies are likely to be formed in both materials. The position of the electronic levels in the band gap due to these defect complexes is shown to correlate well with the experimentally commonly observed broadband luminescence both in GaN and in AlN. The origin of the large bandwidth of the luminescence spectrum is discussed.
408 citations
TL;DR: In this article, the authors reported a study of nitrogen incorporation in GaAs using a N rf plasma source and showed that the N composition can be increased by lowering the growth temperature.
Abstract: We report a study of nitrogen incorporation in GaAs using a N rf plasma source The N composition can be increased by lowering the growth temperature X-ray diffraction shows no phase separation Optical absorption measurements indicate that GaNxAs1−x is a direct band-gap material in the N composition range studied (x⩽148%), rather than a semimetal, contrary to theoretical predictions based on Van Vechten’s model Analyzing the N composition dependence of the band-gap energy of the alloy indicates a composition-dependent bowing parameter, consistent with the first-principles supercell calculations [L Bellaiche, S H Wei, and A Zunger, Phys Rev B 54, 17 568 (1996)]
361 citations
TL;DR: In this paper, an energy distribution of electrons in the conduction band and holes in the valence band is described by a single Fermi distribution with no splitting of quasi-Fermi-energies, but with a temperature different from the lattice temperature.
339 citations
TL;DR: The properties of amorphous carbon (a-C) deposited using a filtered cathodic vacuum arc as a function of the ion energy and substrate temperature are reported in this paper.
Abstract: The properties of amorphous carbon (a-C) deposited using a filtered cathodic vacuum arc as a function of the ion energy and substrate temperature are reported. The sp3 fraction was found to strongly depend on the ion energy, giving a highly sp3 bonded a-C denoted as tetrahedral amorphous carbon (ta-C) at ion energies around 100 eV. The optical band gap was found to follow similar trends to other diamondlike carbon films, varying almost linearly with sp2 fraction. The dependence of the electronic properties are discussed in terms of models of the electronic structure of a-C. The structure of ta-C was also strongly dependent on the deposition temperature, changing sharply to sp2 above a transition temperature, T1, of ≈200 °C. Furthermore, T1 was found to decrease with increasing ion energy. Most film properties, such as compressive stress and plasmon energy, were correlated to the sp3 fraction. However, the optical and electrical properties were found to undergo a more gradual transition with the deposition temperature which we attribute to the medium range order of sp2 sites. We attribute the variation in film properties with the deposition temperature to diffusion of interstitials to the surface above T1 due to thermal activation, leading to the relaxation of density in context of a growth model.
TL;DR: In this paper, a real-space pseudopotential method was used to calculate quasiparticle gaps, self-energy corrections, exciton Coulomb energies, and optical gaps in Si quantum dots.
Abstract: Quasiparticle gaps, self-energy corrections, exciton Coulomb energies, and optical gaps in Si quantum dots are calculated from first principles using a real-space pseudopotential method. The calculations are performed on hydrogen-passivated spherical Si clusters with diameters up to 27.2 \AA{} ( $\ensuremath{\sim}800\mathrm{Si}$ and H atoms). It is shown that (i) the self-energy correction in quantum dots is enhanced substantially compared to bulk, and is not size independent as implicitly assumed in all semiempirical calculations, and (ii) quantum confinement and reduced electronic screening result in appreciable excitonic Coulomb energies. Calculated optical gaps are in very good agreement with absorption data.
TL;DR: In this article, anisotropy of electrical and optical properties in β-Ga2O3 single crystals has been investigated at room temperature, and the conductivity and mobility of the degenerate sample along the direction of b and c axes were investigated.
Abstract: Anisotropy of electrical and optical properties in β-Ga2O3 single crystals has been investigated at room temperature. The conductivity and mobility of the degenerate sample along the direction of b and c axes are 38 Ω−1 cm−1, 46 cm2 V−1 s−1, and 2.2 Ω−1 cm−1, 2.6 cm2 V−1 s−1, respectively. The absorption edges of the insulating sample for light polarized E//b and E//c were 4.79 and 4.52 eV, respectively. The rate of the band gap widening with increasing carrier concentration was much larger for E//b than E//c. The origin of these properties are discussed by considering the crystal and electronic structure of β-Ga2O3.
TL;DR: In this article, the effect of nitrogen addition on the structural and electronic properties of hydrogenated amorphous carbon (a-C:H) films has been characterized in terms of its composition, sp3 bonding fraction, infrared and Raman spectra, optical band gap, conductivity, and paramagnetic defect.
Abstract: The effect of nitrogen addition on the structural and electronic properties of hydrogenated amorphous carbon (a-C:H) films has been characterized in terms of its composition, sp3 bonding fraction, infrared and Raman spectra, optical band gap, conductivity, and paramagnetic defect. The variation of conductivity with nitrogen content suggests that N acts as a weak donor, with the conductivity first decreasing and then increasing as the Fermi level moves up in the band gap. Compensated behavior is found at about 7 at. % N, for the deposition conditions used here, where a number of properties show extreme behavior. The paramagnetic defect density and the Urbach tailwidth are each found to decrease with increasing N content. It is unusual to find alloy additions decreasing disorder in this manner.
TL;DR: The electrical properties and defect structure of selected compositions in the SrTi1−xFexO3−y system (x = 0-0.8) have been studied using van der Pauw 4-point conductivity measurements and electron energy loss spectroscopy (EELS) as mentioned in this paper.
TL;DR: Using scanning tunneling microscopy and reflection high-energy electron diffraction (RHEED), the surface structures of cubic and hexagonal GaN have been studied for the first time as mentioned in this paper.
Abstract: Reconstructions of the GaN(000 ) surface are studied for the first time. Using scanning tunneling microscopy and reflection high-energy electron diffraction, four primary structures are observed: 1 ×1, 3×3, 6×6, and c(6×12). On the basis of first-principles calculations, the 1 ×1 structure is shown to consist of a Ga monolayer bonded to a N-terminated GaN bilayer. From a combination of experiment and theory, it is argued that the 3×3 structure is an adatom-on-adlayer structure with one additional Ga atom per 3×3 unit cell. Gallium nitride and other III-nitrides have attracted considerable interest recently because of their application for blue light-emitting diodes and lasers.[1] These materials have several unique properties compared to the more conventional III-V semiconductors (GaAs, InP, etc.): they exist in both cubic (zincblende) and hexagonal (wurtzite) form, they are refractory, and some of the materials have large band gaps. The relatively small size of nitrogen, compared to Ga or In, in these compounds leads to a number of unique surface structures, which have begun to be explored both experimentally and theoretically for the (001) growth surface of cubic GaN.[2,3] However, for the technologically more relevant (0001) growth surface of hexagonal GaN, very little is known concerning its structure aside from several reports of 2×2 and other reconstructions based on reflection high-energy electron diffraction (RHEED).[4] It is important to understand the surface structures of these materials, since this knowledge will impact our ability to achieve high quality epitaxial growth of the materials as required for optoelectronic applications.
TL;DR: In this article, topology related changes in the local density of states near the ends of closed carbon nanotubes are investigated using spatially resolved scanning tunneling spectroscopy and tight binding calculations.
Abstract: Topology related changes in the local density of states near the ends of closed carbon nanotubes are investigated using spatially resolved scanning tunneling spectroscopy and tight binding calculations. Sharp resonant valence band states are observed in the experiment at the tube ends, dominating the valence band edge and filling the band gap. Calculations show that the strength and position of these states with respect to the Fermi level depend sensitively on the relative positions of pentagons and their degree of confinement at the tube ends.
TL;DR: In this article, the exact Al mole fraction and the biaxial strain of the alloys can be calculated by an additional determination of a, using asymmetric reflections, and the results obtained by x-ray diffraction and elastic recoil detection provide evidence for the validity of Vegard's law in the AlGaN system.
Abstract: AlxGa1−xN alloys were grown on c-plane sapphire by plasma-induced molecular beam epitaxy. The Al content x was varied over the whole composition range (0⩽x⩽1). The molar Al fraction was deduced from x-ray diffraction and for comparison by elastic recoil detection analysis. The composition of the alloys calculated from the lattice parameter c underestimates x. This is due to a deformation of the unit cell. The exact Al mole fraction and the biaxial strain of the alloys can be calculated by an additional determination of a, using asymmetric reflections. The results obtained by x-ray diffraction and elastic recoil detection provide evidence for the validity of Vegard’s law in the AlGaN system. In addition, the deviation of the band gap from a linear dependence on x was investigated. We found a downward bowing with a bowing parameter b=1.3 eV.
TL;DR: In this article, it is suggested that, at low copper ion concentrations, copper ions bound onto the surface of CdS nanoparticles exist as isolated Cu+ ions, which leads to formation of a new, red-shifted, luminescence band.
Abstract: Nonstoichiometric cadmium sulfide nanoparticles ([Cd2+]/[S2-] = 3) in 2-propanol were surface-modified with Cu2+ ions. Addition of copper(II) perchlorate to CdS nanoparticles leads to binding of copper ions onto the surface of the semiconductor, accompanied by rapid reduction of Cu2+ to Cu+, as confirmed by EPR and absorption spectra. Copper(II) perchlorate also quenches the recombination luminescence of CdS nanoparticles effectively. The quenching data obey a static interaction model, which confirms the binding of copper ions onto CdS. The latter was confirmed also by ultrafiltration and ICP spectroscopy. Copper ions bound onto the surface of CdS lead to formation of a new, red-shifted, luminescence band. The maximum of the new band is at 14 700 cm-1 compared to that of the original band at 17 900 cm-1. It is suggested that, at low copper ion concentrations, copper ions bound onto the surface of CdS nanoparticles exist as isolated Cu+ ions. They create a new energy level in the bandgap at about 1.2 eV be...
TL;DR: In this article, it was shown that the Pb s band below the top of the valence band exhibits a series of electronic-structure anomalies relative to the II-VI system, including the occurrence of direct gaps at the L point, anomalous order of band gaps and valence-band maximum energies versus anions, negative optical bowing, and negative band-gap pressure coefficients.
Abstract: The rocksalt-structure PbS, PbSe, and PbTe semiconductors and their alloys exhibit a series of electronic-structure anomalies relative to the II-VI system, including the occurrence of direct gaps at the L point, anomalous order of band gaps and valence-band maximum energies versus anions, negative optical bowing, and negative band-gap pressure coefficients. We show that these anomalies result from the occurrence of the Pb s band below the top of the valence band, setting up coupling and level repulsion at the L point. Furthermore, we find that the topology of the frustrated octahedral structure leads to the occurrence in the random alloy of two distinct bonds for each anion-cation pair and to the predicted stabilization of {ital bulk} ordered Pb{sub 2}STe CuPt-like phase. {copyright} {ital 1997} {ital The American Physical Society}
TL;DR: In this article, the authors present a theoretical model for calculating the band structures of strained quantum-well wurtzite semiconductors, including the strain effects on the shifts of the band edges.
Abstract: We present a theoretical model for calculating the band structures of strained quantum-well wurtzite semiconductors. The theory is based on the Hamiltonian for wurtzite semiconductors and includes the strain effects on the shifts of the band edges. We show new results that include the matrix elements of the Hamiltonian using the finite-difference method for the calculations of the valence electronic band structures of quantum-well wurtzite semiconductors based on the effective-mass theory.
TL;DR: In this article, the dependence of optical characteristics on the structure of atomic layer-deposited titania (TiO 2 ) thin films has been studied and the formation of preferentially oriented crystal (anatase) structure contributes to this increase of refractive index most significantly.
TL;DR: In this paper, the thermoelectric properties of La-filled skutterudites are discussed from the point of view of their electronic structures, and the electronic structure is in turn used to determine transport related quantities.
Abstract: The thermoelectric properties of La-filled skutterudites are discussed from the point of view of their electronic structures. These are calculated from first principles within the local-density approximation. The electronic structure is in turn used to determine transport related quantities. Virtual-crystal calculations for La(Fe,Co)${}_{4}{\mathrm{Sb}}_{12}$ show that the system obeys near rigid band behavior with varying Co concentration, and has a substantial band gap at a position corresponding to the composition LaFe${}_{3}{\mathrm{CoSb}}_{12}.$ The valence-band maximum occurs at the $\ensuremath{\Gamma}$ point and is due to a singly degenerate dispersive band, which by itself would not be favorable for high thermopower. However, very flat transition-metal-derived bands occur in close proximity and become active as the doping level is increased, giving a nontrivial dependence of the properties on carrier concentration and explaining the favorable thermoelectric properties.
TL;DR: In this paper, the authors introduce a new way of band-gap engineering in which they expose a semiconductor quantum well of a direct gap material to a moving potential superlattice modulated in the plane of the well.
Abstract: The dynamics of photogenerated carriers in semiconductor structures with reduced dimensionality has been the subject of intensive investigations in recent years [1,2]. State-of-the-art band-gap engineering technologies enable us to tailor low-dimensional semiconductor systems with desirable optoelectronic properties and study the fundamental aspects of carrier dynamics. This has increased tremendously our fundamental understanding of the dynamic properties of artificial semiconductor structures and has also resulted in a wide range of novel devices such as quantum well lasers, modulators, and detectors, as well as all-optical switches. Nevertheless, the bulk band structure of semiconductors seems to dominate optoelectronic properties since the strength of interband transitions is largely governed by the atomiclike Bloch parts of the wave function [3]. Thus it appears at first glance unavoidable that strong interband optical transitions are linked to direct band-gap semiconductors with short radiative lifetimes such as GaAs, whereas long radiative lifetimes of photogenerated carriers imply utilization of semiconductors with indirect band gaps such as Si and correspondingly reduced interband absorption. Initial attempts to employ band-gap engineering in order to combine strong interband absorption with long radiative lifetimes have focused on so-called doping superlattices [4]. There, alternate n and p doping along the growth direction is utilized to combine a direct gap in momentum space with an indirect gap in real space which causes a spatial separation of photogenerated electron-hole se-hd pairs and hence considerably prolonged lifetimes. Here, we introduce a new way of band-gap engineering in which we expose a semiconductor quantum well of a direct gap material to a moving potential superlattice modulated in the plane of the well. We show that the confinement of photogenerated e-h pairs to two dimensions, together with the moving lateral superlattice, allows reversible charge separation [5]. We demonstrate that the combination of both the advantages of strong interband absorption and extremely long lifetimes of the optical excitations is achieved without affecting the superior optical quality of the quantum well material. The spatial separation of the electron-hole pairs is achieved via the piezoelectric potential of acoustic waves propagating along the surface of a semiconductor quantum well system. On a piezoelectric substrate, the elliptically polarized surface acoustic waves (SAWs) are accompanied by both lateral and vertical piezoelectric fields which propagate at the speed of sound. Those fields can be strong enough to field ionize optically generated excitons and to confine the resulting electrons and holes in the moving lateral potential wells separated by one-half wavelength of the SAW. The spatial separation dramatically reduces the recombination probability and increases the radiative lifetime by several orders of magnitude as compared to the unperturbed case. We further demonstrate that the dynamically trapped electron-hole pairs can be transported over macroscopic distances at the speed of sound and that deliberate screening of the lateral piezoelectric fields of the SAW leads to an induced radiative recombination after long storage times at a location remote from the one of e-h generation. This conversion of photons into a long lived e-h polarization which is efficiently reconverted into photons can serve as an optical delay line operating at sound velocities. The undoped quantum well samples used in our experiments are grown by molecular beam epitaxy on a (100)GaAs substrate. The quantum well consists of 10 nm pseudomorphic In0.15Ga0.85As grown on a 1 mm thick GaAs buffer and is covered by a 20 nm thick GaAs cap layer. The active area of the sample is etched into a 2.5 mm long and 0.3 mm wide mesa (see inset of Fig. 1) with two interdigital transducers (IDTs) at its ends. The IDTs are designed to operate at a center frequency fSAW › 840 MHz. They are partially impedance matched to the 50 V radio frequency (rf) circuitry using an on-chip matching network, thus reducing the insertion
TL;DR: Bond rotation defects close the gap in large-gap nanotubes, open the gap of small-gap Nanotubes and increase the density of states in metallic nanite as discussed by the authors.
Abstract: Bond rotation defects close the gap in large-gap nanotubes, open the gap in small-gap nanotubes, and increase the density of states in metallic nanotubes. Not only are these defects likely to be present in as-grown nanotubes, but they could be introduced locally into intact nanotubes, thereby opening a new road towards device applications. {copyright} {ital 1997} {ital The American Physical Society}
TL;DR: In this paper, the dispersion of the nonlinear refractive index coefficient, n/sub 2/, is measured for both TE- and TM-polarized light and the implications for all-optical switching and spatial soliton propagation are discussed.
Abstract: We report experimental values for the nonlinear optical coefficients of AlGaAs, in the half-band-gap spectral region. The dispersion of the nonlinear refractive-index coefficient, n/sub 2/, is measured for both TE- and TM-polarized light. We observe n/sub 2/(TE)>n/sub 2/(TM) and a ratio of cross-phase modulation to self-phase modulation (TE) of /spl sim/0.95, as predicted from band structure calculations. The spectral dependence of the two- and three-photon absorption coefficients are also measured. Finally, the implications for all-optical switching and spatial soliton propagation are discussed.
TL;DR: In this paper, a transparent conducting thin film of antimony-doped tin oxide has been deposited by the sol-gel dip-coating (SGDC) method, and its optical and electrical properties are analyzed.
TL;DR: In this article, the photonic band gap phenomenon in the visible range in a three-dimensional dielectric lattice formed by close-packed spherical silica clusters was investigated.
Abstract: We report on the photonic band gap phenomenon in the visible range in a three-dimensional dielectric lattice formed by close-packed spherical silica clusters. The spectral position and the spectral width of the optical stop band depend on the direction of light propagation with respect to the crystal axes of opal, and on the relative cluster-to-cavity refraction index n. Manifestations of the photonic pseudogap have been established for both transmission and emission spectra. The stop band peak wavelength shows a linear dependence on n. Transmission characteristics of the lattice have been successfully simulated by numerical calculations within the framework of a quasicrystalline approximation. @S1063-651X~97!13805-3#
TL;DR: In this paper, the authors systematically studied the strain dependence of the free-exciton resonance energies in wurtzite GaN by photoreflectance measurements using well-characterized samples.
Abstract: We have systematically studied the strain dependence of the free-exciton resonance energies in wurtzite GaN by photoreflectance measurements using well-characterized samples. The experimental data have been analyzed using the appropriate Hamiltonian for the valence bands in wurtzite GaN and determined the values of the crystal field splitting, the spin–orbit splitting, the shear deformation potential constants, and the energy gap in the unstrained crystal. Discussions are given on the strain dependence of the energy gaps, of the effective masses, and of the binding energies for the free-exciton ground states as well as on the valence-band parameters.
TL;DR: In this paper, a two-dimensional triangular lattice in GaAs was constructed with a simple holographic recording of a very small number of optical plane waves, and appeared in this regard as the simplest holograms.
Abstract: Photonic band gap materials are holograms with extremely high refractive index contrasts. The refractive index function can be approximated by a small number of plane waves, as a consequence of the photonic crystal periodicity. Photonic crystals can hence be constructed with a simple holographic recording of a very small number of optical plane waves, and appear in this regard as the simplest holograms. Various photonic band gap structures are theoretically analysed and those concepts are illustrated experimentally with the fabrication of a two-dimensional triangular lattice in GaAs. The extension of the method to the three-dimensional diamond structure is discussed.