Band Diagram Calculations Research Articles

A pure 1.5 μm electroluminescence from metal-oxide-silicon tunneling diode using dislocation network

This letter has demonstrated a light emitting diode (LED) with a pure 1.5 μm emission using a metal-oxide-silicon (MOS) tunneling structure based on dislocation network in direct silicon bond wafer. It is found that under negative gate bias, the electrons in the metal gate electrode tunnel through the thin oxide to silicon and then recombine radiatively with holes at the dislocation related states to emit the D1-line with a wavelength of 1.5 μm. The calculation of energy band diagram indicates that a potential well for electrons forms at the charged bonding interface under negative bias, therefore, the electrons tunneled from the gate can rapidly be attracted by the electric field and then confined at the interface, which essentially increases the efficiency of D1 luminescence from MOS tunneling LED. These results are of interest for the development of silicon based photonics with 1.5 μm light emission.

Two-dimensional photonic crystals in antimony-based films fabricated by holography

In this work, we demonstrated the fabrication of two-dimensional (2D) photonic crystals layers (2D-PCLs) by combining holographic recording and the evaporation of antimony-based glasses. Such materials present high refractive indices that can be tuned from 1.8 to 2.4, depending on the film composition; thus, they are interesting dielectric materials for fabrication of 2D-PCLs. The good quality of the obtained samples allowed the measurement of their PC properties through the well-defined Fano resonances that appear in the transmittance spectrum measurements at different incidence angles. The experimental results are in good agreement with the calculated band diagram for the hexagonal asymmetric structure.

Static tuning band gaps of three-dimensional photonic crystals in subterahertz frequencies

Microscale three-dimensional photonic crystals with different dielectric volume fractions (β) were fabricated to tune the band gaps in the subterahertz frequency range. When changed β from 33% to 20% in the SiO2–Al2O3 ceramic-resin photonic crystals with a lattice constant of 500μm, the measured first band gaps were increased from 380–450to450–520GHz. After dewaxing and sintering, the lattice constant of SiO2–Al2O3 ceramic photonic crystals were shrunk to 380μm, and the observed band gaps correspondingly appeared from 470–540GHzto520–600GHz. These experimental results were further confirmed by calculation of band diagrams using the plan wave expansion method.

Microfabrication of Three‐Dimensional Photonic Crystals of SiO2–Al2O3 Ceramics and Their Terahertz Wave Properties

Dense three‐dimensional microphotonic crystals of SiO2–Al2O3 ceramics were fabricated using microstereolithography and successive sintering process. The forming dimensional tolerance for a 50 vol% ceramic paste is 10 μm and sintering shrinkage is around 12%. Diamond‐type photonic crystals with lattice constants of 500 and 125 μm were formed and sintered successfully. The band gaps of the samples were measured and compared with the theoretically calculated band diagram.

Omnidirectional photonic band gap in polymer photonic crystal slabs

In this letter, we report on the experimental observation of a complete in-plane photonic band gap for transverse-electric-like polarized modes in a polymer photonic crystal slab with a triangular array of holes. We performed transmission measurements on two-dimensional photonic crystal slabs in both principal directions of the triangular lattice. For a propagation distance of 40 lattice constants, the transmission was effectively suppressed regardless of propagation direction below −15dB over a bandwidth of 65nm. The experimental results are in excellent agreement with theoretical predictions obtained from band diagram calculations and finite integration time domain techniques.

Exciton dissociation and hole escape in the thermal photoluminescence quenching of(Ga,In)(N,As)quantum wells

The optical properties of $(\mathrm{Ga},\mathrm{In})(\mathrm{N},\mathrm{As})$ quantum wells emitting in the $1.5\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{m}$ range have been investigated by temperature-dependent photoluminescence measurements. The carrier localization at low temperature is attributed to the presence of nitrogen atoms since this process is independent of the indium content and the quantum well thickness. Two different mechanisms are at the origin of the photoluminescence intensity quenching when the temperature rises from $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ to $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The thermal activation energies deduced from Arrhenius plots correspond to the exciton dissociation in the low temperature range and to hole escape from the quantum well to the barrier for temperatures higher than $200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. This interpretation is supported by energy band diagram and exciton binding energy calculations.

Development of 3D Ceramic Photonic Bandgap Structures

The three-dimensional (3D) photonic band gap material is a material that there exists a full photonic band gap in which waves are forbidden to propagate whatever the polarization or the direction of propagation. In order to obtain photonic bandgap in lower range, we focus on the fabrication of PBG materials of diamond structure with TiO2 powder mixed with SiO2. The inverse epoxy structure with periodic diamond lattices in millimeter order has been fabricated by stereolithographic rapid prototyping. TiO2 slurry was filled into the epoxy structure and then cold isostatic pressing was applied. After sintering at 700K for 5hrs, the epoxy was burnt out and the designed structure was maintained perfectly. The calculated band diagram shows that there exists an absolute photonic band gap for all wave vectors. The measurement of transmission from 10 to 20 GHz in <100> direction shows that a complete band gap is formed at about 14.7-18.5 GHz. The magnitude of the maximum attenuation is as large as 30 dB at 17 GHz.

Study on ceramic photonic bandgap structure with three-dimensional diamond lattice

A novel process, which was based on powder injection molding, was investigated for the fabrication of ceramic photonic bandgap structure with three-dimensional diamond lattice. The SiO 2-TiO 2 ceramic powder was mixed with a water-soluble agent to produce slurry. The slurry was then injected into an epoxy mold with inverse diamond lattice, fabricated by the stereolitographic rapid prototyping process. To increase the density of the green compact, cold isostatic pressing was applied on the unit. Using thermal de-binding, the water-soluble agent and the epoxy were extracted at 360 and 650 K, respectively. Sintering was immediately done at 950 K for 5 h and the desired three-dimensional ceramic structure was obtained. The calculated band diagram for this structure indicated the existence of an absolute photonic bandgap for all wave vectors. At 14.7–18.5 GHz, a complete band gap was located with a maximum attenuation of 30 dB at 17 GHz, when transmission was measured in the <100> direction between 10 and 20 GHz.

Nanobox array for silicon-on-insulator luminescence enhancement at room temperature

We report the light extraction enhancement obtained at room temperature from a square lattice of crystalline silicon nanoboxes etched in a silicon-on-insulator substrate. Luminescence spectra recorded under optical pumping show a 125 times emission enhancement as compared with the reference unpatterned silicon-on-insulator emission. In light of band diagram calculations, it is demonstrated that the emission enhancement partially results from the coupling between electron-hole recombination inside the silicon boxes and low group velocity optical modes of the array. Moreover, it is observed that these modes present different decoupling lengths and that a complete extraction of luminescence can be achieved over less than 15μm.

Optical study of ΓL high energy photonic pseudogaps in ZnO inverted opals

We provide experimental evidence of the opening of two new pseudogaps in the high energy region of the ΓL direction in ZnO inverted opals. The appearance of these new pseudogaps is brought about by the increase of refractive index contrast. The calculated band diagram in the ΓL direction, which corresponds to propagation along the (111) crystallographic direction, accounts for the spectral width and position dependence of the pseudogaps on the ZnO fraction present in the opal. To prove this we have performed an optical study by means of reflection and transmission spectroscopy of ZnO inverted opals with different degrees of infiltration. We also study the pseudogap appearing in the highest energy spectral position as a function of sample thickness. In addition, the band engineering developed here allows us to isolate a nondispersive band from the others.

Fabrication of Ceramic Photonic Crystals with Diamond Structure for Microwave Applications

A process for fabricating three‐dimensional photonic crystals composed of SiO2–TiO2‐based ceramics with a diamond structure was investigated. An epoxy structure having an inverse diamond configuration was fabricated by stereolithography, a rapid prototyping method. The epoxy structure was infiltrated with a ceramic slurry and then cold isostatically pressed. After sintering at 670°C for 5 h in air, the epoxy was burned off, leaving behind the desired structure of a ceramic photonic crystal. The calculated band diagram indicated that an absolute photonic band gap for all wave vectors existed. The measurement of transmission in the 〈100〉 direction from 10 to 20 GHz showed that a complete band gap formed at about 14.7–18.5 GHz. The magnitude of the maximum attenuation was as large as 30 dB at 17 GHz, which indicated that the fabricated structure worked well as a photonic crystal.

Applications of the finite difference mode solution method to photonic crystal structures

The finite difference waveguide mode solution method, which has been popularly employed in the study of waveguide modes on various optical and dielectric waveguides, is utilized to calculate the modal characteristics of photonic crystal fibers (PCFs) and planar photonic crystal waveguides and the band diagrams of two-dimensional photonic crystals. Vector guided modes on both PCFs based on the total internal reflection guiding mechanism ('holey fibers') and those resulting from photonic band gap effect are accurately computed, with their effective indexes and field distributions compared with other methods. Calculated dispersion of a single-core holey fiber and coupled-power behavior of a two-core holey fiber are found to agree with measured results. For applications to band diagram calculation and planar photonic crystal waveguide analysis, the finite difference scheme is modified simply by imposing suitable periodic boundary condition. Numerical results for air-column crystals and dielectric-rod crystals are both found to agree well with calculations using other methods.

Rayleigh Multipole Methods for Photonic Crystal Calculations

Abstract—Multipolemethodshaveevolvedtobeanimportantclassof theoretical and computational techniques in the study of photoniccrystalsandrelatedproblems. Inthischapter,wepresentasystematicand unified development of the theory, and apply it to a range ofscatteringproblemsincludingfinitesetsofcylinders,two-dimensionalstacks of grating and the calculation of band diagrams from thescattering matrices of grating layers. We also demonstrate its utilityin studies of finite systems that involve the computation of the localdensityofstates.1 Introduction2 TheoreticalFormulation2.1 BackgroundandContext2.2 GeneralFramework2.3 InfiniteStructures—Arrays2.4 InfiniteStructures—Gratings2.5 InfiniteStructureswithComplexUnitCell2.6 InfiniteStructures—CrossedGratingsand“Woodpiles”3 FromScatteringMatricestoBandDiagrams4 DisorderedPhotonicCrystals5 Green’s Tensor and Local Density of States for 2DPhotonicCrystals5.1 Background5.2 LDOSforTMPolarisation5.3 LDOSforTEPolarisation6 DiscussionandOutlook

Measurement of Built-in Electrical Potential in Cu(In, Ga)Se2 Solar Cells

AbstractThe built-in electrical potential on cross sections of Cu(In, Ga)Se2 (CIGS) solar cells was measured quantitatively and resolved spatially using scanning Kelvin probe microscopy. In the conditions of open and short circuits, no significant potential variation on the p-n junction was probed due to the surface Fermi-level pinning. With an external reverse-bias voltage applied to the device, we were able to probe the potential on the junction; the potential profiles demonstrate that the p-n junction is a buried homojunction, located 30-80 nm from the CIGS/CdS interface in the CIGS film. The potential measurement over the CdS and ZnO layers, which is consistent with the band diagram calculations, indicates that the CdS and ZnO layers are inactive for the collection of photoexcited carriers.

High magnetic field studies of two-dimensional electron gas in a GaN/GaAlN heterostructure: Mechanisms of parallel conduction

We report on quantum Hall effect (QHE) and Shubnikov–de-Haas (SdH) measurements for a GaN/GaAlN heterostructure in high magnetic fields (up to 35 T). The observed well defined SdH oscillations, correlated with QHE plateaus, confirm the existence of a two-dimensional electron gas at the GaN/GaAlN interface. The Shubnikov–de-Haas oscillations are superimposed on a strong positive magnetoresistance. We show that this positive magnetoresistance can be linked to a parallel conduction channel. The analysis of the high magnetic field data yields information about the carrier concentration and mobility in this channel. The concentration and mobility of two-dimensional gas and the parallel conduction layer are analyzed in a wide temperature range (1.9–77 K). A physical model (based on the band diagram and mobility calculations) explaining the origin of parallel conduction is presented.

Energy spectrum of a GaAs (δ-Sn) structure on a vicinal face

The potential profile, electron energy levels, and corresponding wave functions are calculated for a gallium-arsenide structure with a δ-doped tin vicinal face GaAs(0.3°, δ-Sn). Calculated values of the electron densities in the subbands agree well with the quantities obtained from an analysis of the Shubnikov-de Haas oscillations and photoluminescence spectra of the structure. On the basis of the calculated band diagram the lines observed in the photoluminescence spectrum of the GaAs(0.3°, δ-Sn) structure are identified here for the first time as associated with electron transitions on the size-quantization levels in the tin δ-layer.

Formation of a Schottky barrier between eutectic Ga,In and thiophene oligomers

The formation of a Schottky barrier between an eutectic (Ga,In) alloy and a highly doped thiophene oligomer is followed as a function of time using current density–voltage and capacitance–voltage measurements. Within 1 h, the diode characteristics change from almost nonrectifying, leaky behavior into a rectification ratio of 104 with a considerably reduced leakage current. Measurements and energy band diagram calculations show that the depletion width increases with time due to a decrease in the ionizable acceptor density of the semiconductor at the Schottky interface. This is probably caused by a chemical reaction between the in-diffusing metals and the doped oligomer.

Possibility of InP-Based 2-Dimensional Photonic Crystal: An Approach by the Anodization Method

We have investigated the possibility of InP-based 2-dimensional (2D) photonic crystal experimentally and theoretically. To fabricate such crystal, we aimed at utilizing triangular rods and holes automatically formed at the surface of (111)A InP substrate by an anodization method. Favorable characteristics are that the rods and holes orient perpendicular to the surface and have submicron width and high aspect ratio. In addition, observed photoluminescence spectra indicated negligibly slow surface recombination at the anodized surface. From the calculation of band diagram, the photonic gap was found for uniform triangular rods. Thus low-damage 2D photonic crystal which controls light emission and propagation in the 2D plane can be realized by controlling the size uniformity and position of rods using the patterned oxide mask.

GaSb/GaInSb quantum wells grown by metalorganic vapor phase epitaxy

Single and multiple quantum wells of GaSb/GaInSb were grown by metalorganic vapor phase epitaxy. X-ray diffraction on an 80 Å single well confirmed the Ga1−xInxSb composition to be x=0.15, for which the lattice mismatch is ≊1.0%. Photoluminescence and photoconductivity from this sample both showed a signal due to carriers in the well, the position of which was in good agreement with the calculated band diagram. Shubnikov–de Haas oscillations in the transverse magnetoresistance (ρxx) of a four-period multiquantum well, and the associated quantum Hall effect, indicated that a two-dimensional hole gas was present in one of the wells. Unusually, the strongest oscillations were seen for occupancy of an odd number of (spin split) Landau levels (ν=1,3,5,...,etc.) This sample also showed luminescence peaks at 738 and 755 meV which were attributed to recombination in the wells.

Characterization of anisotype and isotype Hg0.8Cd0.2Te/CdTe heterojunctions

The metallurgical heterojunction located between liquid phase epitaxial Hg0.8Cd0.2Te films and CdTe substrates is characterized electrically and electro-optically for the first time. This compositionally graded heterojunction is found to have zero bias resistance-area R0A products ranging from 102 to 105 Ω cm2 at 300 K, and from 106 to 109 Ω cm2 at 100 K. Between these two temperatures thermal activation energies of approximately 0.4 eV and 0.1 eV are measured. Measurements of capacitance, photoresponse position, and spectral sensitivity lead to the conclusion that a charge-separating depletion region and valence band barrier are located within the transition region, and are associated with the high R0A products. These conclusions are supported by numerically calculated band diagrams.