X-ray Rocking Curve Measurements Research Articles

Characterization of lattice mosaic ofa-plane GaN grown onr-plane sapphire by metalorganic vapor-phase epitaxy

AbstractNonpolara-plane GaN films were grown on r-plane sapphire substrates by atmospheric metalorganic vapor-phase epitaxy. The as-grown layers were studied by high-resolution x-ray diffraction. Thea-plane GaN lattice mosaic is orientation dependent as determined by x-ray rocking curve (XRC) measurements. The tilt mosaic measured with the c-axis within the scattering plane (c-mosaic) was greater than the mosaic measured with the m-axis within the scattering plane (m-mosaic). The mosaic along both azimuths decreased and thec-mosaic/m-mosaic ratio was increased with increase of growth temperature from 1050 °C to 1080 °C. The morphological transition was correlated to change in thea-plane GaN tilt mosaic measured by XRC.

Growth and laser-assisted liftoff of low dislocation density AlN thin films for deep-UV light-emitting diodes

The growth of AlN thin films on (0 0 0 1) sapphire by metal-organic chemical vapor-phase epitaxy has been investigated to serve as the template layer of deep-ultraviolet light-emitting diodes. Delayed coalescence of AlN films resulted in a low threading dislocation density of 5×10 9 cm −2 for a 2.1 μm thick film compared to partially coalesced 1.05 μm films exhibiting a threading dislocation density of 1.1×10 10 cm −2. The reduction in dislocation density results from a decrease in the number of edge character threading dislocations, while the screw character density remains virtually unchanged, as determined by X-ray rocking curve measurements of the AlN off-axis ( 2 0 2 ¯ 1 ) and on-axis (0 0 0 2) reflections, respectively. Cross-sectional transmission electron microscopy indicates the presence of a number of inversion domains in the AlN films. Electrically injected, 317 nm Al x Ga 1− x N LEDs were successfully fabricated, with a maximum output power of 17.7 μW tested on wafer at 160 mA DC. Using a 248 nm KrF excimer laser, a 2.8 μm thick AlN film was debonded from the sapphire substrate using a laser pulse power of 1 J/cm 2. However, substrate debonding of an Al x Ga 1− x N/AlN LED layer could not be achieved.

Homoepitaxial Growth of GaN Layers by Reactive Molecular-Beam Epitaxy on Bulk GaN Single Crystals Prepared by Pressure-Controlled Solution Growth

We have performed the homoepitaxial growth of GaN layers by reactive molecular-beam epitaxy (MBE) on both sides (Ga- and N-faces) of the bulk GaN single crystals prepared by the pressure-controlled solution growth (PC-SG) method. High-crystalline-quality GaN layers, which showed a narrow full-width at half maximum (FWHM) for the (002) plane in X-ray rocking curve measurements and no dark spot in the cathodoluminescence images, were obtained both on the Ga- and N-faces. It was indicated that the incorporation mechanism of residual impurities and/or defects is different between the homoepitaxial layers on the Ga- and N-faces, and that a larger amount of residual donors and nonradiative recombination centers existed in the homoepitaxial layer on the N-face. In addition, our results suggest that the poor quality of N-polarity GaN epilayers grown by conventional MBE is caused not only by the high density of nanometric inversion domains (IDs) in the N-polarity matrix, but also by polarity-related effects.

Pulsed Laser Deposition of High-Quality (K,Na)NbO3 Thin Films on SrTiO3 Substrate Using High-Density Ceramic Targets

High-quality (K,Na)NbO3 thin films were successfully deposited on a (100) SrTiO3 (STO) substrate by pulsed laser deposition. High-density KNbO3 (KN), (K0.5Na0.5)NbO3 (KNN) and NaNbO3 (NN) ceramic targets were prepared by spark plasma sintering (SPS). The crystallographic analyses of the film were performed by conventional X-ray diffraction (XRD) analysis and rocking curve measurement. The XRD reciprocal space map was also measured to determine the lattice constants of the film and analyze the crystallographic relationship between the grown film and the STO substrate. The fluctuation change in the orientation of crystals in the grown film decreased and the smoothness of the film surface improved with increasing sodium content of the film. For the NN films, the full width at half maximum (FWHM) of the rocking curve was as small as 0.12°. The XRD reciprocal space map measurements showed that the lattices of the KN and KNN films relaxed on the STO substrate but the NN film was restricted to it.

Growth of terbium aluminum garnet (Tb 3Al 5O 12; TAG) single crystals by the hybrid laser floating zone machine

Incongruent melting of terbium aluminum garnet (Tb 3Al 5O 12; TAG) single crystals has the largest Verdet constant, based on the Faraday rotation, among “transparent” materials, even though no practically applicable size of TAG single crystal has yet been grown. To grow TAG single crystals, we designed a hybrid laser floating zone growth machine, in which four CO 2 gas lasers and four halogen lamps were placed around a pedestal. This is capable of both uniform laser heating and lamp pre-heating. We successfully grew TAG single-crystal rods of 3 mm in diameter, which were suitable for the use in optical devices. The crystals showed a full-width at half-maximum in as little as 27 arcsec by the X-ray rocking curve measurement. The examined growth directions were randomly dispersed under the no-seed utilized growth condition. Several optical property evaluations confirmed successful results for high transmittance qualities and a larger Verdet constant than the conventional Tb 3Ga 5O 12 crystals.

Growth of terbium aluminum garnet (Tb3Al5O12; TAG) single crystals by the hybrid laser floating zone machine

Incongruent melting of terbium aluminum garnet (Tb3Al5O12; TAG) single crystals has the largest Verdet constant, based on the Faraday rotation, among “transparent” materials, even though no practically applicable size of TAG single crystal has yet been grown. To grow TAG single crystals, we designed a hybrid laser floating zone growth machine, in which four CO2 gas lasers and four halogen lamps were placed around a pedestal. This is capable of both uniform laser heating and lamp pre-heating. We successfully grew TAG single-crystal rods of 3 mm in diameter, which were suitable for the use in optical devices. The crystals showed a full-width at half-maximum in as little as 27 arcsec by the X-ray rocking curve measurement. The examined growth directions were randomly dispersed under the no-seed utilized growth condition. Several optical property evaluations confirmed successful results for high transmittance qualities and a larger Verdet constant than the conventional Tb3Ga5O12 crystals.

Growth of high-quality AlN with low pit density on SiC substrates

We investigated the optimum growth condition and initial growth process of AlN on 6H-SiC(0 0 0 1) substrates prepared by H 2 etching in the plasma-assisted molecular beam epitaxy (MBE). In X-ray rocking curve measurements, a small full-width at half-maximum of about 50 arcsec was obtained for a 150 nm thick AlN layer. The AlN layers have contained a lot of pits over a grown surface. Pit densities were markedly decreased by reducing the amount of residual impurities (O, OH and H 2O) in an MBE chamber. A very low pit density of 10 4–10 5 cm −2 was realized.

High-Quality ZnO Layers Grown on 6H-SiC Substrates by Metalorganic Chemical Vapor Deposition

In this letter, the 6H-SiC substrate has been studied for the growth of the ZnO layer. The X-ray diffraction measurement clearly showed the c-axis oriented growth of ZnO layers on SiC(0001) substrates. The X-ray rocking curve measurement diffracted a smaller full-width at half maximum of the ZnO layers grown on SiC than that of the same layers grown on the conventional Al2O3 substrate with metalorganic chemical vapor deposition (MOCVD). A distinct free-exciton emission was dominantly observed even at room temperature (RT) while the donor-bound-exciton peaks were disappeared at around ∼120 K. In addition, no deep-level emission was observed even at RT in the ZnO/SiC samples. These optical and crystalline properties have hardly been observed in the ZnO/Al2O3 samples grown by MOCVD. Therefore, the higher quality of the ZnO layers grown on SiC might be attributed to the smaller lattice mismatch of ∼5% as well as the +c surface orientation in ZnO/SiC sample geometry.

Observation of spontaneous ordering in the optoelectronic material GaInNP

We report a detailed structural and optical characterization of high-quality GaInNP films. These films were grown by gas-source molecular-beam epitaxy on GaAs (100) substrates. These epitaxial layers were then characterized by a high-resolution x-ray rocking curve (HRXRC) and photoluminescence (PL) measurements. With nitrogen incorporation, the PL peak redshifts, indicating bandgap reduction and the line-width broadening increases due to alloy scattering. The anisotropic properties of the polarized HRXRC and polarized piezoreflectance spectra are used to prove the spontaneous ordering in GaInP incorporating nitrogen. Furthermore, ordering-induced superlattice-like microstructure shown in high-resolution transmission electron microscope images is used to confirm the spontaneous ordering in Ga0.44In0.56NxP1−x epitaxial layers.

High‐quality AlN epitaxial films on (0001)‐faced sapphire and 6H‐SiC substrate

This paper presents crystal qualities of high-quality AlN epitaxial films on (0001)-faced sapphire and6H-SiC substrates. The AlN epitaxial films are grown using a low-pressure metal organic vapor phase epitaxy (LP-MOVPE) method. 0.5–1 μm-thick AlN films without any cracks are realized on both substrates. Both of AlN films are found to have similar crystal qualities in spite of large difference in in-plane lattice mismatch between AlN and each substrate. The AlN films have an atomically flat surface with clear atomic steps. Results of X-ray rocking curve (XRC) measurement indicate that both of the AlN films have small tilted mosaicity, however relatively large twisted mosaicity. Dislocation density of the AlN films in its surface region is approximately as low as 1 × 1010 cm−2 and most of dislocations consist of edge-type dislocations. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

TEM characterization of InN films grown by RF‐MBE

Structural properties of InN films grown on (0001) sapphire by radio frequency molecular beam epitaxy were characterized using transmission electron microscopy. A high density of threading dislocations was observed in the InN films. The density of the dislocation was more than 2 × 1010 cm−2. Most threading dislocations were edge-type dislocations. A columnar structure of crystallites with a small angular distribution in the c-plane (twist) was clearly observed. X-ray rocking curve measurements showed that InN film had relatively large distribution of twist in contrast to that of tilt. Convergent beam electron diffraction method was used to determine the polarity of the InN film. It is found that the InN film grown on the sapphire (0001) substrate showed N-polarity. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Postgrowth annealing of defects in ZnO studied by positron annihilation, x-ray diffraction, Rutherford backscattering, cathodoluminescence, and Hall measurements

Defects in hydrothermal grown ZnO single crystals are studied as a function of annealing temperature using positron annihilation, x-ray diffraction, Rutherford backscattering, Hall, and cathodoluminescence measurements. Positron lifetime measurements reveal the existence of Zn vacancy related defects in the as-grown state. The positron lifetime decreases upon annealing above 600 °C, which implies the disappearance of Zn vacancy related defects, and then remains constant up to 900 °C. The Rutherford backscattering and x-ray rocking curve measurements show the improvement of crystal quality due to annealing above 600 °C. Although the crystal quality monitored by x-ray diffraction measurements is further improved after annealing at above 1000 °C, the positron lifetime starts to increase. This is due to either the formation of Zn vacancy related defects, or the change of the Zn vacancy charge state occupancy as a result of the Fermi level movement. The electron concentration increases continuously with increasing annealing temperature up to 1200 °C, indicating the formation of excess donors, such as oxygen vacancies or zinc interstitials. The cathodoluminescence measurements reveal that the ultraviolet emission is greatly enhanced in the same temperature range. The experimental results show that the ZnO crystal quality, electrical and optical characteristics are improved by postgrowth annealing from 600 to 1200 °C. The disappearance of Zn vacancy related defects contributes to the initial stage of improved crystal quality.

Aluminum nitride substrate growth by halide vapor transport epitaxy

High-quality AlN layers with thickness up to 50 μm have been grown by HVTE at growth rates up to 60 μm/h at deposition temperatures of 1000–1100°C in the pressure range of 50–760 Torr. The HVT process uses an aluminum chloride amine adduct as the aluminum source and ammonia for the nitrogen. This new technique eliminates the main difficulties of the conventional HVPE growth, where aluminum oxidation and the strong reactivity of aluminum chloride with quartz create the potential for oxygen contamination. The crystalline layer quality as determined by X-ray rocking curve measurement shows FWHM of 300–900 and 500–1300 arcsec for (0 0 2) and (1 0 2) planes, respectively.

Either step-flow or layer-by-layer growth for AlN on SiC (0001) substrates

ABSTRACTAlN was grown on 4H- or 6H-SiC (0001) on-axis substrates by plasma-assisted molecular beam epitaxy. By utilizing optimized SiC surface pretreatment, RHEED oscillations just after the growth of AlN were obtained with high reproducibility. This study focused on the growth kinetics of AlN and the correlation between kinetics and the crystalline quality of the grown layers. It was found that the growth mode changed from layer-by-layer to step-flow for high growth temperatures, while for lower temperatures the layer-by-layer growth mode persisted. The mechanism responsible for the change in growth mode is discussed. Symmetrical (0002) and asymmetrical (01–14) x-ray rocking curve measurements were carried out to evaluate the crystalline quality. For the (0002) peak, both high-temperature and low-temperature grown layers showed almost the same FWHM values. On the other hand, for the (01–14) peak, the FWHM of low-temperature grown AlN was much smaller (180 arcsec) than that of the high-temperature grown AlN (450 arcsec).

Correlation between the type of threading dislocations and photoluminescence characteristics at different doping concentrations of Si in GaN films

At various doping concentrations of Si in GaN films, the correlation between the type of dislocations and photoluminescence (PL) characteristics was investigated. A different broadening behavior of symmetric and asymmetric Bragg peaks as a function of carrier concentration provided qualitative evidence that the type of threading dislocations generated in GaN layers was strongly dependent on the doping levels of Si. PL spectra in conjunction with x-ray rocking curve measurements suggested that the yellow luminescence associated with deep levels was more strongly related with edge dislocations than screw or mixed ones.

Structural and optical characterization for vapor-phase proton exchanged lithium niobate waveguides

We have studied the crystalline phase transition for vapor-phase proton exchanged (VPE) lithium niobate waveguide by using pure benzoic acid. The VPE layers in the z-cut lithium niobate crystal have been characterized by X-ray rocking curves, OH− bond infrared absorption, and prism coupling measurements. The crystalline quality assessment by the X-ray rocking curve measurement shows desirable κ2 phase formation for nonlinear optical waveguide applications. It has been observed that the crystalline phase makes a transition from the κ2 to the β phase with the increase in the vapor-phase exchange time. The prism coupling measurement also showed a step-like index profile for our VPE samples. From the step index profile, we deduced an effective diffusion coefficient of 0.14μm2h−1, which is twice than that of the previously reported value. Shift in the OH− bond absorption wavelength with crystalline phase change and the increase in absorption with the exchange time were also observed from our spectrophotometer measurement.

Single crystals of triple-layered cuprates Bi 2Sr 2Ca 2Cu 3O 10+ δ: growth, annealing and characterization

The growth of Pb-free Bi 2Sr 2Ca 2Cu 3O 10+ δ (Bi-2223) single crystals has been investigated using the travelling solvent floating zone technique under mixed gas flow of argon and oxygen. Slow growth rates of 0.20, 0.10, 0.06 and 0.04 mm/h were applied to four growth runs. Nearly single-phase Bi-2223 crystals sized up to 10×6×0.5 mm 3 were obtained using a slow growth rate of 0.04 mm/h and subsequent annealing. The crystals were characterized by energy dispersive X-ray, X-ray diffraction (XRD), transmission electron microscopy, magnetic susceptibility and resistivity measurements. It is found that the growth rate affects the phase formation of Bi-2223 crystals. Both XRD and magnetic susceptibility measurements show that the as-grown crystals obtained at a slow growth rate of 0.04 mm/h consist of >90% Bi-2223 phase, whereas as-grown crystals obtained at rates of 0.10 and 0.20 mm/h contain predominantly Bi-2212, Ca 2CuO 3 and a small quantity of Bi-2223 phase. Post-annealing experiments were carried out at 500–850 °C for 120–500 h in an effort to improve the crystal quality with respect to phase purity and oxygen homogeneity. A phase-transformation process from Bi-2212 to Bi-2223 was observed. The results of XRD and susceptibility measurements show that the relative fraction of the Bi-2223 phase increases upon increased annealing temperature and/or prolonged annealing time while the Bi-2212 phase diminishes gradually, resulting in crystals that were of 98–99% Bi-2223 phase. Such a phase transformation from Bi-2212 into Bi-2223 might be explained via a layer-intercalation mechanism. The refinement results of XRD data show that pure-phase Bi-2223 crystals have orthorhombic symmetry with lattice parameters of a=5.408(2) Å, b=5.413(7) Å, and c=36.868(1) Å. Narrow full width at half maximum of 0.16–0.20° determined from X-ray rocking curve measurements demonstrates the high crystallinity of Bi-2223 crystals. The superconducting transition temperature T c increases from 102 K for as-grown crystals to 110 K for crystals annealed at 850 °C for 500 h in O 2 flow. The in-plane and out-of-plane resistances as a function of temperature measured on annealed crystals show that the general features of the resistivity of Bi-2223 crystals are similar to those of Bi-2212 crystals.

Ferromagnetic resonance and microstructural studies of Ag/Fe–GaAs waveguide structures

We report the growth and characterization of ferromagnetic iron/silver (Ag/Fe) multilayer structures on gallium arsenide (GaAs) (100) substrates by molecular beam epitaxy. The samples have been characterized by x-ray diffraction and ferromagnetic resonance (FMR) techniques. X-ray read-camera studies have demonstrated the epitaxial nature of crystalline Fe film grown on GaAs substrate, while x-ray rocking curve measurements reveal a narrow linewidth of only 0.3°. On the FMR technique, we focused specifically on the information contained in FMR linewidth ΔH(f ). Experimental results on ultrathin Fe/Ag films have been obtained with sufficient resolution to measure the linewidth broadening due to intrinsic damping. FMR linewidth is resolved to vary between 0.5 and 1.1 GHz in a frequency range of 20 GHz. Frequency-dependent FMR linewidth ΔHpp(ω) shows a typical linear dependence with a zero frequency offset ΔH(0) of almost zero value, indicating a near-perfect crystalline quality of the deposited magnetic film. The Gilbert damping parameter G is extracted to be 1.45×108 s−1 from the slope of the curve.

Aluminum Nitride Crystal Growth by Halide Vapor Transport Epitaxy

AbstractHalide vapor transport epitaxy (HVTE) is demonstrated for growth of AlN layers with thickness up to 50 μm at deposition rates up to 60 μm/h. The HVTE process uses an aluminum chloride amine adduct as the aluminum source of both aluminum and nitrogen. This new technique eliminates the main difficulties of the conventional hydride VPE growth, where aluminum oxidation and the strong reactivity of aluminum chloride with fused silica create the potential for oxygen contamination. This study shows the effect of temperature, gas flow velocities, and reactor pressure on the growth rate and layer quality. It is found that the growth rate and the layer quality strongly depend on the gas ratio. The species of carrier gas, the flow rates and partial pressures can be used as tools to optimize growth rate and to avoid any etching effects resulting from reverse chemical reactions. The crystalline layer quality as determined by x-ray rocking curve measurement shows FWHM of 300–900 and 500–1300 arc-sec for (002) and (102) planes, respectively.PACS: 81.05.Ea; 81.15.Kk; 68.55.Jk.

MoO 3–Li 2O flux LPE growth of YIG films and its characterization

Pure-Yttrium iron garnet (Y 3Fe 5O 12; YIG) films were grown from a MoO 3–Li 2O flux onto (1 1 1) GGG substrate using liquid phase epitaxy. By investigating the [Fe 2O 3]/[Y 2O 3] molar ratio of the flux, we were able to successfully grow stoichiometric and high-purity YIG films. Evaluations and calculations of lattice mismatch along the 〈1 1 1〉, 〈0 0 1〉, and 〈1 1 0〉 directions using X-ray rocking-curve measurements revealed that these values differed significantly from one another. This clearly indicated that structural deformation had occurred in the YIG films. The deformation was larger in the films grown from the MoO 3–Li 2O flux than in those grown from a PbO–B 2O 3 flux. However, the impurity concentration in the former was one hundred times less than that in the latter. Thus, because of this purity, the YIG films grown from the MoO 3–Li 2O fluxes are preferable for use in optical and microwave devices.