bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dry etching of N‐face GaN using two high‐density plasma etch techniques
Authors: Rizzi F. , Bejtka K. , Semond F. , Gu E. , Dawson M. D. , Watson I. M. , Martin R. W. 
Published: January 2007

AbstractThis paper describes processing of GaN on the on the (000$ \bar 1 $) N‐face surface, using two different high‐density plasma etch techniques, inductively coupled plasma (ICP) etch, and electron cyclotron resonance (ECR) etching. ICP experiments used several different conditions employing Cl2–Ar–BCl3 or Cl2–Ar plasmas. The resulting maximum etch rates of 370–390 nm/min are approximately twice as high as etch rates for Ga‐face (0001) GaN with the same recipes. ECR etching employed a Cl2–CH4–Ar recipe, which produced an average etch rate of 55 nm/min in a 20‐minute etch process on N‐face GaN. Both etch techniques increased the roughness of N‐face GaN, but could produce surfaces with average roughness values below 3 nm. Selection of conditions with a dominant chemical etch contribution is important to maintain smooth surfaces. The use of both ICP and ECR etching in sequence is advantageous in situations where a GaN substrate several tens of microns in thickness must be thinned from the backside, stopping the etch in a suitable marker layer. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Improvement of surface light extraction from flip‐chip GaN‐based LED by embossing of thermosetting polymers
Authors: Bao Kui , Zhang Bei , Wang ZhiMin , Dai Tao , Kang XiangNing , Chen ZhiZhong , Xu Ke , Ji Hang , Chen Yong , Gan ZiZhao 
Published: January 2007

AbstractIn this report, a further improvement of surface light extraction from flip‐chip GaN‐based LED was obtained by the micro patterning of encapsulation on the sapphire. The two dimensional taper arrays with period from 6 to 10 micron were successfully realized on polymer encapsulation by a simple and low cost technique so called embossing of thermosetting polymers. As a preliminary demonstration, at least 1.74 enhancement of the surface output intensity was achieved in the 1 mm × 1 mm GaN‐based LED device under the injection current of 350 mA. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Focused ion beam etched nitride/air DBRs as cavity mirror facets of violet InGaN/GaN multiple‐quantum well laser diodes
Authors: Dai Tao , Zhang Bei , Zhang ZhenSheng , Xu Jun , Chen WeiHua , Li Rui , Bao Kui , Wei QiYuan , Xu Ke , Hu XiaoDong , Yang ZhiJian , Kang XiangNing , Pan YaoBo , Lu Min , Zhang GuoYi , Gan ZiZhao 
Published: January 2007

AbstractWe report on the demonstration of focused ion beam (FIB) etched nitride/air distributed Bragg reflector (DBR) gratings as cavity mirror facets of violet InGaN/GaN multiple quantum wells edge emitting laser diodes (LD). The nitride/air DBRs consisted of fifth order Bragg semiconductor wall and third order Bragg air gap with the depths around 1.2 micron to 1.5 micron were successfully achieved by focused Ga ion beam (FIB) milling as backside laser facets on GaN‐based laser diodes. Under pulsed current injection at room temperature, sharp laser emissions were observed at the wavelength between 398 to 401 nm. The threshold currents of stripe and ridge lasers with nitride/air DBR mirror facets were found to be respectively lower than the related LDs with cleaved facets. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cathodoluminescence study of InGaN MQW laser diodes using laser lift‐off technique
Authors: Li Rui , Chen Weihua , Kang Xiangning , Xu Ke , Xu Jun , Yang Zhijian , Nie Ruijuan , Yu Tongjun , Chen Zhizhong , Qin Zhixin , Zhang Guoyi , Gan Zizhao , Hu Xiaodong 
Published: January 2007

AbstractIn this paper, spatially integrated or spatially resolved cathodoluminescence (CL) spectroscopy were employed to evaluate the structural and optical changes of InGaN multiple quantum well (MQW) structure before and after Laser lift‐off (LLO) process. As for a partially strain‐relaxed In0.1Ga0.9N MQW laser diode (LD) structure with cracking in underlying epitaxial layers, LLO did not cause the blue shift in CL spectra as expected, but rather the red shift induced by the indium diffusion from its abundant regions around cracks. This result could be proved by the monochromated scanning CL images taken at 390 nm and 408 nm not having the same obvious complementary as those of original ones. Compared with calculated laser fluence for LLO, this phenomenon could be mainly attributed to the easy penetration of laser energy via cracks and consequent irradiation absorption within MQWs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A comparative study of the internal quantum efficiency for the green MQWs grown on sapphire and FS‐GaN substrates
Authors: Jeong Yong‐Hee , Lee Hae‐Yong , Park Jae‐Young , Jeong Jong‐Pil , Hong Chang‐Hee , Suh Eun‐Kyung 
Published: January 2007

AbstractWe observed the green MQWs grown on FS‐GaN substrates leading to less generation of dislocation, V‐defect, and stacking fault than those on sapphire by AFM and TEM. The temperature‐dependent PL spectral peak energies of the green MQWs grown on FS‐GaN substrates reveal more clear “S”‐shaped behaviors due to stronger carrier localization than those on sapphire substrates. Also, the green MQWs grown on FS‐GaN have the higher internal quantum efficiency (IQE) of 9 ∼ 12% in compared to those grown on sapphire at the same MQW thickness and wavelength of 530 ∼ 540 nm. These results will be due to the effects of the enhanced carrier localization and the reduced quantum confined stark effect (QCSE) by reason of the optical‐loss reduction as decreasing the defect density and the piezoelectric field reduction as decreasing the relaxation of strain. We could identify that the green MQWs grown on FS‐GaN substrates have the superior characteristics of the optics, structure, and surface to those on sapphire substrates. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Initial growth stages of MOVPE InN studied by AFM and specular reflectivity
Authors: van der Lee A. , Salah F. , Harzallah B. , Ruffenach S. , Briot O. 
Published: January 2007

AbstractThe initial growth of InN grown by MOVPE was investigated by a combination of atomic force microscopy (AFM) and X‐ray specular reflectivity for five different thin films ranging from 57 to 750 Å. Both AFM and specular reflectivity measurements show that during the initial growth the surface is not completely covered but that instead a discontinuous layer resembling quasi two‐dimensional islands is formed. Dots with heights between 30 and 100 nm appear at the same time; the number density of these dots decreases with increasing thickness. At 750 Å the surface is completely covered and obtains a granular aspect. The surface coverage of the discontinuous wetting layer is discussed in relation with the apparent porosity calculated from the specular reflectivity data. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High indium content AlInGaN films: growth, structure and optoelectronic properties
Authors: Nemoz M. , Beraudo E. , De Mierry P. , Vennéguès P. , Hirsch L. 
Published: January 2007

AbstractStructural and optical properties of AlInGaN epilayers grown on GaN template on sapphire substrate by metalorganic vapour phase epitaxy (MOVPE) are investigated by photoluminescence (PL), photothermal deflection spectroscopy (PDS), X‐ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy (TEM). At low substrate temperature during the growth two quaternary layers are presents along the growth axis. The interface layer strained on GaN contains about 12% Al and 24% In. The surface layer with a 3D morphology disappears increasing the substrate temperature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Improved AlN buffer layer technologies for UV‐LEDs
Authors: Ranalli F. , Parbrook P. J. , Wang T. , Bai J. , Lee K. B. , Airey R. J. , Hill G. , Tahraoui A. , Cullis A. G. 
Published: January 2007

AbstractGrowth of AlGaN based structure on AlN buffers grown directly on sapphire is reported. Such buffers show excellent morphology but a high density of edge dislocations. Growth of GaN on such layers allows dislocation bending and annihilation. Improved UV emission compared to structures grown on GaN prepared conventionally has been observed. Using AlGaN on ALN gives significantly less dislocation reduction, but efficient 340 nm LEDs have been fabricated on this template. For further dislocation reduction overgrowth on a porous AlN film has been developed, leading to much improved room temperature luminescence, indicating the technology's potential for UV‐LED device fabrication (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Analysis of the relation between leakage current and dislocations in GaN‐based light‐emitting devices
Authors: Lee S. W. , Oh D. C. , Goto H. , Ha J. S. , Lee H. J. , Hanada T. , Cho M. W. , Hong S. K. , Lee H. Y. , Cho S. R. , Choi J. W. , Choi J. H. , Jang J. H. , Shin J. E. , Lee J. S. , Yao T. 
Published: January 2007

AbstractIn order to understand the origin of leakage current, light emitting devices were grown on two different templates with apparently different dislocation density: one on thin GaN template (∼2 μm) with higher dislocation density (low × 109 cm–2) prepared by metal‐organic vapor‐phase epitaxy (sample A), and the other on thick GaN template (∼20 μm) with comparatively low dislocation density (high × 108 cm–2) by hydride vapor‐phase epitaxy (sample B). Especially, the template B showed very low value of the dislocation density for a screw component, 2.2 × 107 cm–2 evaluated by transmission electron microscope and 2.3 × 107 cm–2 approximated by the Williamson‐Hall plot which was evaluated by high resolution X‐ray diffraction, respectively. On the other hand, sample A showed one order higher, low × 108 cm–2, than that of sample B for a screw component. Sample A showed the larger leakage current (more than two orders of magnitude) than sample B in a forward‐biased region and a reverse‐biased region also. It is expected that the screw dislocation were strongly contributed to the leakage current of forward and reverse I‐V regions in LEDs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Monolithic white light emitting diodes with a broad emission spectrum
Authors: Dussaigne A. , Brault J. , Damilano B. , Massies J. 
Published: January 2007

AbstractMonolithic white light emitting diode (LEDs) grown by molecular beam epitaxy (MBE) is an original approach to realize white LEDs. Using a Ga0.8In0.2N/GaN multi‐quantum well (QW) structure with different QW thicknesses in the active region of a GaN p‐n junction leads to white light emission provided that the different QW emission wavelengths and relative intensities are properly adjusted. However, the color rendering index (CRI) and the output power are still a limitation for the development of these LEDs. In this study, we propose to use a broad emission spectrum – from blue to red – with the objective of improving the CRI. Carrier recombination mechanisms in the LEDs are studied by electroluminescence (EL) measurements at room temperature and discussed as a function of the structure design. Results show a strong modification of the EL spectrum as a function of the applied voltage and an enhancement of the red emission component with the insertion of a GaN undoped spacer layer between the active region and the p‐type layers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical gain and saturation behavior in homoepitaxially grown InGaN/GaN/AlGaN laser structures
Authors: Świetlik T. , Perlin P. , Suski T. , Leszczyński M. , Czernecki R. , Grzegory I. , Porowski S. 
Published: January 2007

AbstractOptical gain and losses in semiconductor laser epilayers are of profound importance in device optimization. We used both parameters to estimate the potential of InGaN/GaN/AlGaN epitaxial system to be used as a laser structure emitting in a blue region. The sample was grown homoepitaxially by MOVPE technique on high quality bulk GaN substrates obtained in high pressure growth process. These structures are characterized by very low dislocation density (around 105 cm–2). As a result the reduction of a nonradiative recombination is expected which is reflected in reduced excitation pump power and gain saturation processes described by means of saturation length and a product of the latter and a maximum modal gain. To determine gain value and its saturation behavior a variable stripe length method is used employing one dimensional amplifier model. Maximum gain value of 190 cm–1 together with internal losses of 15 cm–1 are determined for the studied structure. Low value of maximum saturation length of 320 um was found in our structures. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
ZnMgO‐ZnO quantum wells embedded in ZnO nanopillars: Towards realisation of nano‐LEDs
Authors: Bakin A. , El‐Shaer A. , Mofor A. C. , Al‐Suleiman M. , Schlenker E. , Waag A. 
Published: January 2007

AbstractZnO thin films, ZnMgO/ZnO heterostructures and ZnO nanostructures were fabricated using molecular beam epitaxy (MBE), vapour phase transport (VPT) and an aqueous chemical growth approach (ACG). The possibility to employ several fabrication techniques is of special importance for the realization of unique device structures. MBE was implemented for ZnO‐based layer and heterostructure growth. Pronounced RHEED oscillations were used for growth control and optimisation, resulting in high quality ZnO and Zn1–xMgxO epilayers and heterostructures, as well as ZnMgO/ZnO quantum wells on sapphire and SiC substrates. A novel advanced VPT approach is developed and sapphire, SiC, ZnO epitaxial layers, and even plastic and glass were implemented as substrates for ZnO growth. The VPT fabrication of ZnO nanopillars, leading to well aligned, c‐axis oriented nanopillars with excellent quality and purity is demonstrated. Successful steps were made towards device fabrication on ZnO basis. The nanopillar fabrication technique is combined with MBE technology: MBE‐grown ZnMgO/ZnO quantum well structures were grown on ZnO nanopillars presenting significant progress towards nano‐LEDs realization. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Radiative lifetime in wurtzite GaN/AlN quantum dots
Authors: Bardoux R. , Bretagnon T. , Guillet T. , Lefebvre P. , Taliercio T. , Valvin P. , Gil B. , Grandjean N. , Damilano B. , Dussaigne A. , Massies J. 
Published: January 2007

AbstractWe study wurtzite GaN/AlN quantum dots (QDs) by time‐resolved photoluminescence. The properties of nitride based nano‐objects are significantly affected by strong built‐in electric fields existing in this crystalline phase. These fields induce a spatial separation of electrons and holes in the quantum dot, a Stark shift of the transition energy, and they slow their radiative recombination down to tens of microseconds of decay time for the largest quantum dots. Such long decay times are responsible for the screening of internal fields by using moderate excitation intensities, thus modifying drastically both the energy and the rate of photon emission. Consequently it is difficult to perform spectroscopic studies of these QDs in the regime where a single electron‐hole (e‐h) pair is present at the most in each dot. Using a pulsed laser excitation, we study the time‐resolved dynamics of carrier recombinations, waiting for complete recombination of all electron‐hole pairs in the dots. We clearly exhibit the conditions where no screening of the internal electric field occurs. We especially obtain the transition energy and the mono‐exponential decay, i.e the radiative recombination time, of the last e‐h pair present in the dot, for a wide range of QD sizes. These results are analyzed within an envelope function model for the electron and hole confinement. The effective electric field, averaged over the strain distribution in the dots, is determined to be of 9.0 ± 0.5 MV/cm. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Quantum well‐free nitride‐based UV LEDs emitting at 380 nm
Authors: de Mierry Philippe , Tinjod Frank , Chenot Sébastien , Lancefield David 
Published: January 2007

AbstractCVD. The bare chip device shows a strong UV emission at 380 nm, with a maximum output power of 1.6 mW at 140 mA, and a junction temperature of 120 °C. The saturation of the external quantum efficiency (EQE) occurs at 0.5 kA/cm2 (∼80 mA), a much higher value than the 10 A/cm2 commonly reported in quantum wells (QWs) based nitride LEDs. This behavior can be accounted for by a temperature dependent non‐radiative recombination rate which increases at high injection currents. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photonic crystals comprising selectively grown flat‐topped and sharp‐tipped GaN pyramids
Authors: Coquillat D. , Le Vassor d'Yerville M. , Boubanga Tombet S. A. , Liu C. , Bejtka K. , Watson I. M. , Edwards P. R. , Martin R. W. , Chong H. M. H. , De La Rue R. M. 
Published: January 2007

AbstractSelective area growth offers the promise of producing III‐nitride photonic crystals (PhCs) without dry etching and concomitant surface damage. Two PhC structures were studied, one comprising an array of flat‐topped GaN micropyramids with micrometre‐scale periodicity, and the other made up of sharp‐tipped pyramids with sub‐micrometre periodicity. Angularly resolved reflection and transmission measurements revealed the presence of sharp resonances associated with resonant Bloch modes. As a result, the photonic band structure was determined along symmetry directions of the reciprocal lattice for the two PhC structures. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Strong coupling in bulk GaN microcavities grown on silicon
Authors: Réveret F. , Sellers I. R. , Disseix P. , Leymarie J. , Vasson A. , Semond F. , Leroux M. , Massies J. 
Published: January 2007

AbstractWe have studied GaN microcavities grown on silicon by angle resolved reflectivity at 5 and 300 K. A Bragg mirror made up of λ/4 AlGaN and AlN layers has been grown on a silicon substrate. The GaN active layer whose thickness is equal to λ/2 is covered by a 100 Å thick aluminium layer which acts as the top mirror. Transfer matrix simulations are carried out to interpret the reflectivity spectra from which crucial parameters of the active layer such as the oscillator strengths, the excitonic energies and the associated broadenings of A and B excitons are deduced. At low temperature the strong coupling regime between with A and B excitons and the cavity photonic mode is clearly observed. At room temperature the splitting is evaluated to 45 meV. In order to get further insight in the physics of nitride‐based microcavities and especially to improve the exciton‐photon coupling, the influence of the Bragg or metallic mirrors on the cavity is analysed. The inhomogeneous broadening of excitons together with the strain gradient experienced by the active layer along the growth axis are also investigated. All of these effects on the Rabi splitting are analysed and discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Temperature‐ and excitation density dependency of photoluminescence spectra in InGaN/GaN‐heterostructures
Authors: Vierheilig C. , Braun H. , Schwarz U. T. , Wegscheider W. , Baur E. , Strauß U. , Härle V. 
Published: January 2007

AbstractWe study the lateral diffusion of photogenerated carriers within InGaN/GaN quantum wells by scanning in the focal plane of our confocal microscope. The photoluminescence (PL) images are analyzed at varying excitation densities in the temperature range between 4 K and room temperature. The results of a blue and a green emitting sample are discussed in context of reported diffusion lengths for InGaN/GaN quantum wells. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Efficiency enhancement of 400 nm violet LEDs utilizing island‐like GaN thick film by HVPE technology
Authors: Tsay Jenq‐Dar , Liu Po Chun , Guo Yih‐Der , Wang Jing‐Mei , Liu Wen‐Yueh , Pan Shyi‐Ming , Wu Liang‐Wen , Heuken Michael 
Published: January 2007

AbstractIn this study, we develop a novel way to fabricate InGaN/GaN LED chips with special shape for improving the output power. Crack‐free shaped GaN islands were first prepared on c‐axis sapphire substrate by using HVPE selective area growth. By doing so, GaN islands with flat top surface and inclined side faces are obtained. Then, the InGaN/GaN LED structure was grown on the top surface of the GaN island subsequently. The output powers of the p‐side up and the p‐side down shaped LED chip are 1.4 and 2.2 times the output power of the cubic chip, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth kinetics and properties of ZnO/ZnMgO hetero‐ structures grown by radical‐source molecular beam epitaxy
Authors: Ivanov S. V. , El‐Shaer A. , Shubina T. V. , Listoshin S. B. , Bakin A. , Waag A. 
Published: January 2007

AbstractA phenomenological approach to quantitative description of Zn(Mg)O growth by radical‐source molecular beam epitaxy, based on the experimental studies of RHEED intensity oscillations, has been developed. It allows a precise control of growth rate, composition and stoichiometry at any growth temperature, Along with optimization of a growth initiation procedure on a c‐sapphire, it is necessary condition for fabrication of high quality ZnO epilayers and ZnO/ZnMgO heterostructures in a wide Mg composition range. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Blue light emitting diodes on Si(001) grown by MOVPE
Authors: Schulze F. , Dadgar A. , Bertram F. , Bläsing J. , Diez A. , Veit P. , Clos R. , Christen J. , Krost A. 
Published: January 2007

AbstractThe cover picture of this issue of physica status solidi (c) has been taken from the article [1].