MOCVD Growth of GaN on Sapphire Using a Ga2O3 Interlayer

Metalorganic chemical vapor deposition (MOCVD) was used to grow crystalline GaN on a Ga2O3 interlayer deposited by pulsed laser deposition. The Ga2O3 interlayer situated between undoped GaN (u-GaN) and sapphire can be etched out during the chemical lift-off process. A ((2) over bar 01) oriented beta-Ga2O3 thin film was first deposited on the sapphire; this was followed by u-GaN growth via MOCVD carried out in an N-2 atmosphere to prevent the decomposition of Ga2O3. Using transmission electron microscopy (TEM), the orientation relationship was observed to be GaN[11 (2) over bar0] parallel to Ga2O3[010] where the lattice mismatch between the two materials was 8.5%. The full width at half maximums of the x-ray rocking curve at the GaN (0002) plane and of the photoluminescence spectrum measured from GaN/Ga2O3/sapphire were 1444 arcsec and 8.3 nm, respectively; these were almost identical to the measured values for GaN/sapphire fabricated in an N-2 environment. It was concluded that the growth atmosphere played a more important role in determining the crystallinity of u-GaN than the Ga2O3 thin film underneath. Finally, an InGaN light-emitting diode structure was successfully fabricated on the GaN/Ga2O3/sapphire. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.073111jes] All rights reserved

GaN Epilayer Grown on Ga2O3 Sacrificial Layer for Chemical Lift-Off Application

GaN-on-sapphire structure with a Ga2O3 sacrificial layer was employed for the chemical lift-off process application. The ((2) over bar 01) beta-oriented Ga2O3 thin film was first deposited on the c-plane sapphire substrate using pulsed laser deposition, followed by the GaN growth via metalorganic vapor phase epitaxy under N-2 and H-2 environment in sequence. From the transmission-electron-microscopy observation, the orientation relationship between GaN and beta-Ga2O3 was identified as GaN[11 (2) over bar0]parallel to Ga2O3[010]. A GaN epilayer with an electroplated copper substrate was demonstrated using a chemical lift-off process where the Ga2O3 sacrificial layer can be laterally etched out with a hydrofluoric solution. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.002111esl] All rights reserved

Transferring Thin Film GaN LED Epi-Structure to the Cu Substrate by Chemical Lift-Off Technology

In this paper, a patterned sacrificial layer structure comprised of 3 mu m-wide SiO(2) narrow strips and 3 mu m spacing between strips fabricated on sapphire substrate was proposed. The structure was used not only to improve GaN epilayer quality, but also as a sacrificial layer structure. The GaN light emitting diodes (LEDs) covered by the Cu substrate was fabricated after the GaN epitaxy layer was grown on the sapphire by lateral epitaxial overgrowth. Chemical etching using hydrofluoric acid was conducted to remove the aforementioned SiO(2) strips, and hence transform them into narrow tunnels. The GaN LEDs with the Cu substrate detached from the sapphire substrate after interface strain was increased, which demonstrates that n-side-up vertical GaN LEDs could be more easily obtained using chemical lift-off technology without laser damage compared with the laser lift-off technique. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3582352] All rights reserved

Surface texturing for wafer-bonded vertical-type GaN/mirror/Si light-emitting diodes

An n-side-up GaN/mirror(Pd/Au)/Si light-emitting diode (LED) with surface texturing has been fabricated by a combination of wafer-bonding, laser lift-off, and surface texturing techniques. Two concentrations of KOH solution were used to roughen the n-GaN surface. In order to obtain a uniformly roughened surface, the solution was heated instead of being subjected to photoirradiation. The GaN/Pd/Au/Si LEDs with surface texturing exhibited a maximum luminance intensity of 130 mcd (at 20 mA) with a forward voltage of 3.2 V. The luminance intensity is over two times larger than that of the original planar GaN/sapphire LEDs (at 20 mA). Under high current injection, the surface textured GaN/Pd/Au/Si LEDs also showed a more stable luminance intensity. This feature is attributed to the Si substrate providing a good heat sink and surface roughening enhancing the external quantum efficiency. Furthermore, the n-side-up GaN/mirror(Pd/Au)/Si LEDs with surface texturing have been demonstrated to have high reliability

Defect reduction of laterally regrown GaN on GaN/patterned sapphire substrates

Structural properties of GaN epilayers on wet-etched protruding and recess-patterned sapphire substrates (PSSs) have been investigated in detail using high-resolution double-crystal X-ray diffraction (DCXRD) and etch-pit density methods. The DCXRD results reveal various dislocation configurations on both types of PSSs. The etch pits of GaN on the recess PSS exhibit a regular distribution, i.e. less etch pits or threading dislocation density (TDD) onto the recess area than those onto the sapphire mesas. On the contrary, an irregular distribution is observed for the etch pits of GaN on the protruding PSS. A higher crystal quality of the GaN epilayer grown onto the recess PSS can be achieved as compared with that onto the protruding PSS. These data reflect that the GaN epilayer on the recess PSS could be a better template for the second epitaxial lateral overgrowth (ELOG) of GaN. As a result, the GaN epilayers after the ELOG process display the TDDs of around similar to 10(6) cm(-2). (C) 2009 Elsevier B.V. All rights reserved

Effects of fluorine-implanted treatment on Ba0.7Sr0.3TiO3 films

The effects of F-ion implantation on the leakage and dielectric properties of the Ba0.7Sr0.3TiO3 (BST) films were investigated. The BST film implanted with 1 x 10(15) cm(-2) shows the optimum leakage performance. The leakage current density can be decreased by one order of magnitude as compared to that of the non-implanted sample at an applied voltage of 2 V. On increasing the implanted dose from 5 x 10(14) to 5 x 10(15) cm(-2), the dielectric constant first increases and then decreases due to the deteriorated crystallinity. It is found that the suitable F-ion dose can reduce the -OH contaminants and improve the dielectric and leakage properties. (C) 2000 Elsevier Science Ltd. All rights reserved

Cross-linked and uncross-linked biodegradable nanocomposites. I. Nonisothermal crystallization kinetics and gas permeability

Various nanocomposites of poly(butylene succinates) (PBS) with different ratios of organically modified layered silicates (OMLS) were prepared. Moreover, such PBS nanocomposites cross-linked by dicumyl peroxide (DCP) were also prepared in this work. Effects of cross-linking and OMLS on nonisothermal crystallization kinetics and the gas permeability of PBS samples were investigated further. WAXD indicates that the layers of clay were intercalated by the modifiers, and that the interlayer distance of OMLS in the nanocomposites could be expanded to about 2.96 nm. The results of DSC analysis revealed that the crystallization temperature of nanocomposites shifted to the lower temperature with the increase of OMLS content. With the addition of OMLS, crystallinity was decreased, whereas the half-life of crystallization was increased. On the other hand, even the cross-linked effects also increased the half-life of crystallization of the materials, but did not necessarily decrease crystallinity in all cases. Moreover, the PBS/OMLS nanocomposites showed a 23.87-46.64% decrease in permeability of oxygen when compared with the pristine PBS sample. Yet, the crosslinked nanocomposites exhibited decrements of 6.3839.53%. This indicates that the gas permeability of PBS was more effectively depressed by the addition of OMLS than by the cross-linking reaction. The cross-linked structure of polymer seemed not to be very effective in decreasing the gas permeability of FIBS. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 1069-1079, 200

Ion-implanted treatment of (Ba, Sr)TiO3 films for DRAM applications

The effects of ion implantation on the properties of spin-on sol-gel Ba0.7ST0.3TiO3 (BST) thin films were studied by implanted Ar+, N+, and F+ doses. The F+-implanted BST samples present leakage current density 450. The leakage current of F+-implanted BST samples was reduced about one order of magnitude as compared with that of samples with implanted Ar+, N+ or without implantation. The thickness shrinkage from 135 to 115 nm was observed in F+-implanted BST films (before annealing treatment) and a respective increase in the refractive index from 1.84 to 2.05 was measured. After annealing the implanted samples, the changes of thickness and refractive index depend on the concentration of implanted dose. Based on an infrared transmission study of the samples we suggest that the ion-implanted samples with smaller dose (5 x 10(14) cm(-2)) have fewer -OH contaminants than the non-implanted or implanted samples with the larger doses (greater than or equal to1 x 10(15) cm(-2)). Based on the results presented, we conclude that suitable ion implantation densities the spin-on sol-gel BST films and reduces the -OH contaminants in the films. (C) 2001 Elsevier Science B.V. All rights reserved

Ion-implantation treatment (Ba, Sr)TiO3 thin films

The effects of ion-implantation on the properties of spin-on sol-gel (Ba, Sr),TiO3 (BST) thin films were studied by implanting with Ar+, N+ and F+ doses. The F+ implanted BST samples present better electrical and dielectric properties than the A(+) or Nt implanted BST do. The pronounced thickness shrinkage was observed in BST films after the F+ implantation (before annealing treatment) and a respective increase in the refractive index was measured. After the implanted samples are annealed, the changes of thickness and refractive index depend on the concentration of the implanted dose. If the F+ implanted dose is low (similar to5 x 10(14) cm(-2)), the BST preserves the densification propel-ties. Its refractive index increases to 2.23 and it also presents a high dielectric constant of about 520. If the F+ implanted dose is high (greater than or equal to similar to1 x 10(15) cm(-2)), excess F+ ions form Sr or Ba bondings with F+. This will degrade the material, electric and dielectric properties. The corresponding dielectric constant is about 440. An infrared transmission study of the samples suggests that the ion-implanted sample with lower doses have fewer -OH contaminants than the non-implanted or implanted samples with high doses. Based on the results presented, it was concluded that suitable ion-implantation densifies the spin-on sol-gel BST films and reduces the -OH contaminants in the films

Characterization of NH3 plasma-treated Ba0.7Sr0.3TiO3 thin films

The effects of plasma surface treatment, using NH3 gas, of Ba0.7Sr0.3TiO3 (BST) films on the leakage and dielectric characteristics of a Pt/BST/Pt capacitor were investigated. As a result of the exposure of BST to the plasma, the leakage current density of the BST capacitor can be improved by three orders of magnitude as compared to that of the nonplasma-treated sample at an applied voltage of 1.5 V. Nevertheless, the surface morphology of BST was also changed by the NH3 plasma, as explored by atomic force microscopy. From the X-ray photoelectron spectroscopy examination, the existence of the N 1 s peak was observed in the plasma-treated sample. It induces the additional space charge and results in the reduction of the dielectric constant. (C) 2000 Elsevier Science Ltd. All rights reserved