Light extraction of GaN LEDs with 2-D photonic crystal structure

Ultraviolet photo-lithography is employed to introduce two-dimensional (2D) photonic crystal (PC) structure on the top surface of GaN-based light emitting diode (LED). PC patterns are transferred to 460-nm-thick transparent indium tin oxide (ITO) electrode by inductively coupled plasma (ICP) etching. Light intensity of PC-LED can be enhanced by 38% comparing with the one without PC structure. Rigorous coupled wave analysis method is performed to calculate the light transmission spectrum of PC slab. Simulation results indicate that total internal reflect angle which modulated by PC structure has been increased by 7 degrees, which means that the light extraction efficiency is enhanced outstandingly.

Full-color emission from In2S3 and ln(2)S(3): Eu3+ nanoparticles

New observations on the luminescence Of In2S3 and europium-doped In2S3 nanoparticles show a green (5 10 nm) emission from In2S3 and In1.8Eu0.2S3 nanoparticles while a blue (425 nm) emission is observed from ln(1.6)Eu(0.4)S(3) nanoparticles. Both the blue and green emissions have large Stokes shifts of 62 and 110 nm, respectively. Excitation with longer-wavelength photons causes the blue emission to shift to a longer wavelength while the green emission wavelength remains unchanged. The lifetimes of both the green and blue emissions are similar to reported values for excitonic recombination. When doped with Eu3+, in addition to the broad blue and green emissions, a red emission near 615 nm attributed to Eu3+ is observed. Temperature dependences on nanoparticle thin films indicate that with increasing temperature, the green emission wavelength remains constant, however, the blue emission shifts toward longer wavelengths. Based on these observations, the blue emission is attributed to exciton recombination and the green emission to Indium interstitial defects. These nanoparticles show full-color emission with high efficiency, fast lifetime decays, and good stability; they are also relatively simple to prepare, thus making them a new type of phosphor with potential applications in lighting, flat-panel displays, and communications.

Investigations on V-defects in quaternary AlInGaN epilayers

The characteristics of V-defects in quaternary AlInGaN epilayers and their correlation with fluctuations of the In distribution are investigated. The geometric size of the V-defects is found to depend on the In composition of the alloy. The V-defects are nucleated within the AlInGaN layer and associated with threading dislocations. Line scan cathodoluminescence (CL) shows a redshift of the emission peak and an increase of the half width of the CL spectra as the electron beam approaches the apex of the V-defect. The total redshift decreases with decreasing In mole fraction in the alloy samples. Although the strain reduction may partially contribute to the CL redshift, indium segregation is suggested to be responsible for the V-defect formation and has a main influence on the respective optical properties. (C) 2004 American Institute Of Physics.

Effect of critical thickness on structural and optical properties of InxGa1-xN/GaN multiple quantum wells

InGaN/GaN multiquantum-well (MQW) structures grown by metalorganic chemical-vapor deposition on n-type GaN and capped by p-type GaN were investigated by cross-sectional transmission electron microscopy, double crystal x-ray diffraction, and temperature-dependent photoluminescence. For the sample with strained-layer thicknesses greater than the critical thicknesses, a high density of pure edge type threading dislocations generated from MQW layers and extended to the cap layer was observed. These dislocations result from a relaxation of the strained layers when their thicknesses are beyond the critical thicknesses. Because of indium outdiffusion from the well layers due to the anneal effect of Mg-doped cap layer growth and defects generated from strain relaxation, the PL emission peak was almost depressed by the broad yellow band with an intensity maximum at 2.28 eV. But for the sample with strained-layer thicknesses less than the critical thicknesses, it has no such phenomenon. The measured critical thicknesses are consistent with the calculated values using the model proposed by Fischer, Kuhne, and Richter. (C) 2004 American Institute of Physics.

Effects of TMIn flow on the interface and optical properties of InGaN/GaN mutiple quantum wells

The effects of pre-TMIn flow prior to QW growth and TMIn flow rates during QW growth on the interface and optical properties of InGaN/GaN MQWs were investigated. Pre-depositing indium prior to QW growth and an appropriate TMIn flow rate can improve the interface abruptness and increase the EL intensity. InGaN/GaN MQWs with improved interface abruptness have increasing emission intensity and wavelength. We attribute the interface improvement and the increase of EL intensity to the improvement of the indium compositional profiles. (C) 2004 Elsevier B.V. All rights reserved.

Cleaved-edge overgrowth of aligned InAs islands on GaAs(110)

A novel approach for positioning InAs islands on GaAs(110) by cleaved-edge overgrowth is reported. The first growth sample contains a strained InxGa1-xAs/GaAs superlattice of varying indium fraction and thickness, which acts as a strain nanopattern for the cleaved edge overgrowth. The formation of aligned islands is observed by means of atomic force microscopy. The ordering of the aligned islands and the structure of a single InAs island are found to depend on the properties of the underlying InxGa1-xAs/GaAs superlattice and molecular beam epitaxy growth conditions.

Synthesis of GaN nanowires and nano-pyramids in a two-hot-boat chemical vapor deposition system via an in-doping technique

A two-hot-boat chemical vapor deposition system was modified from a thermal evaporation equipment. This system has the advantage of high vacuum, rapid heating rate and temperature separately controlled boats for the source and samples. These are in favor of synthesizing compound semiconducting nano-materials. By the system, we have synthesized high-quality wurtzite single crystal GaN nanowires and nanotip triangle pyramids via an in-situ doping indium surfactant technique on Si and 3C-SiC epilayer/Si substrates. The products were analyzed by x-ray diffraction, field emission scanning electron microscopy, highresolution transmission electron microscopy, energy- dispersive x-ray spectroscopy, and photoluminescence measurements. The GaN nanotip triangle pyramids, synthesized with this novel method, have potential application in electronic/ photonic devices for field-emission and laser.

A novel method for positioning of InAs islands on GaAs(110)

A novel method for positioning of InAs islands on GaAs (110) by cleaved edge overgrowth is reported. The first growth sample contains strained InxGa1-xAs/GaAs superlattice (SL) of varying indium fraction, which acts as a strain nanopattern for the cleaved-edge overgrowth. Atoms incident on the cleaved edge will preferentially migrate to InGaAs regions where favorable bonding sites are available. By this method InAs island chains with lateral periodicity defined by the thickness of InGaAs and GaAs of SL have been realized by molecular beam epitaxy (MBE). They are observed by means of atomic force microscopy (AFM). The strain nanopattern's effect is studied by the different indium fraction of SL and MBE growth conditions. (c) 2005 Elsevier B.V. All rights reserved.

Investigations on optical properties of AlGaInN epilayers grown by mocvd

Microscopic luminescence and Raman scattering study was carried on AIInGaN quaternary alloy. Based on the analyses of SEM image and cathodoluminescence spectra measured around V-defects, the correlation between V-defect formation and indium segregation was clarified. Raman scattering of thin AlInGaN epilayers was investigated by using the short wavelength excitation of 325nm laser line. The frequency shift of A(1)(LO) phonon induced by the change of Al composition in alloy was observed. The Raman scattering of LO phonons was found to be resonantly enhanced with outgoing resonance, and it is attributed to the cascade-like electron-multiphonon interaction mechanism.

Photoluminescence characteristics of InP annealed in phosphorus and iron phosphide ambiences

Photo luminescence (PL) spectroscopy has been used to study InP annealed in phosphorus and iron phosphide ambiences. Noticeable PL emissions related with thermally induced defects have been detected in undoped InP annealed in iron phosphide ambience. Origins of the PL emissions have been discussed. (c) 2004 Elsevier Ltd. All rights reserved.

Growth and characterization of InN on sapphire substrate by RF-MBE

Indium nitride (InN) films were grown on sapphire substrates by radio-frequency plasma-excited molecular beam epitaxy (RF-MBE). Atomic force microscopy (AFM), reflection high-energy electron diffraction (RHEED), double-crystal X-ray diffraction (DCXRD) and photoluminescence (PL) spectroscopy were used to characterize the InN films. The results show that the InN films have good crystallinity, with full-width at half-maximum (FWHM) of InN (0 0 0 2) DCXRD peak being 14 arcmin. At room temperature, a strong PL peak at 0.79eV was observed. At 1.9eV or so, no peak was observed. In addition, it is found that the InN films grown with low-temperature (LT) InN buffer layer are of better quality than those without LT-InN buffer layer. (c) 2004 Elsevier B.V. All rights reserved.

Carrier channels of multimodal-sized quantum dots: A surface-mediated adatom migration picture

This paper focuses on the study of carrier channels of multimodal-sized quantum dots formed on patterned substrate by a rate-equation-based model. Surface-mediated indium adatom migration is revealed by a direct comparison between quantum dot wetting layer, which acts as carrier channel, formed on a flat substrate and on a patterned substrate. For the assessment of suitability, the carrier channel of the dot-in-well structure has also been studied by the present model, and the transition energies of the carrier channel (e.g., InGaAs quantum well) obtained from theoretical simulation agree fairly well with those obtained from the reflectance measurements.

Calculation of energy levels in InGaAs/GaAs quantum dot array

The subbands of the ground state E-c1, the first excited state E-c2 and heavy hole state E-HH1 are calculated by solving the eigenvalues of effective-mass Hamiltonian H-0 which is derived from eight-band k . p theory and the calculations are performed at k(x) = k, = k = 0 for the three-dimensional array of InGaAs/GaAs quantum dots (QDs). With indium content in InGaAs QDs gradually increasing from 30% to 100%,the intersubband transition wavelength of E-c2 to E-c1, blue-shifts from 18.50 to 11.87 mu m,while the transition wavelength of E-c1, to E-HH1, red-shifts from 1. 04 to 1. 73 mu m. With the sizes of Ir-0.5 Ga-0.5 As and InAs QDs increasing from 1.0 to 5.0 nm, the intersubband transition from E-c1, to E-C2 transforms from bound-state-to-continuum-state to bound-state-to-bound-state, and the corresponding intersubband transition wavelengths red-shift from 8.12 pm (5.90 pm) to 53.47 mu m (31.87 pm), respectively, and the transition wavelengths of E-C1 to E-HH1 red-shift from 1. 13 mu m (1.60 mu m) to 1.27 mu m (2.01 mu m), respectively.

Thermally induced Fe atom transition from substitutional to interstitial sites in InP and its influence on material property

As-grown Fe-doped semi-insulating InP single crystal has been converted into n-type low-resistance material after high temperature annealing. Defects in the InP materials have been studied by conventional Hall effect measurement, thermally stimulated current spectroscopy, deep level transient spectroscopy and X-ray diffraction respectively. The results indicate that Fe atoms in the InP material change from the substitutional to the interstitial sites under thermal activation. Consequently, the InP material loses its deep compensation centers which results in the change in types of conduction. The mechanism and cause of the phenomena have been analyzed through comparison of the sites of Fe atom occupation and activation in doping, diffusion and ion implantation processes of InP.

The correlation between preferred orientation and performance of ITO thin films

The tin-doped indium oxide (ITO) thin films were prepared by reactive thermal evaporation on the glass substrates. The effects of substrate temperatures (T-s) on the grain preferred orientation, the electrical and optical properties of ITO films were studied. X-ray diffraction (XRD) patterns indicated that the preferred orientation of film changes from (222) to (400) as T, > 200 degrees C. It can be explained by that the low-index crystallographic planes are easier to be formed when the adatoms have high surface mobility. The Hall measurements indicated that both the concentration and mobility of carrier increase with increasing T,,,. The grain orientation of film does not influence the transmissivity and the carrier concentration, but enhances the carrier mobility. The transmissivity of ITO films is over 90% in the visible wavelength region (except that of the film deposited at 125 degrees C). A minimum resistivity of 5 X 10-4 Omega cm is achieved for the (400) preferred orientation film. Thus, the highest figure of merit of 3.5 x 10(-2) square/Omega is obtained for the film with (400) preferred orientation. The correlation between the preferred orientation and electrical and optical properties are discussed.