bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimization of SiGe Graded Buffer Defectivity and Throughput by Means of High Growth Temperature and Pre-Threaded Substrates
Authors: Erdtmann Matthew , Currie Matthew T. , Woicik Joseph C. , Black David 
Published: April 2011

ABSTRACTDislocation glide kinetics dictate in relaxed graded buffers a fundamental opposition between the defectivity and throughput. For state-of-the-art Si-based applications, the trade-off between defect level and wafer cost (inversely related to throughput) has made the insertion of SiGe graded buffers into production difficult. We aim to mitigate the trade-off by reporting two advances that enable simultaneous improvements in both defectivity and throughput. The first is use of a high growth temperature to allow very fast dislocation glide velocities and growth rates as high as 1.0 μm/min. The second is the use of “pre-threaded” Si substrates, substrates with an elevated density of threading dislocations. By having dislocation nucleation controlled by uniformly distributed substrate threading dislocations, instead of unpredictable heterogeneous sources, impediments to dislocation glide, such as dislocation bundles and pile-ups, are reduced. By incorporating both advances into SiGe graded buffer epitaxy, dislocation pile-up densities are reduced by nearly three orders of magnitude, threading dislocation densities are reduced by a factor of 7.4×, and wafer throughput is increased at least 33%.
Short-period AlGaN based superlattices for deep UV light emitting diodes grown by gas source molecular beam epitaxy
Authors: Nikishin Sergey , Borisov Boris , Kuryatkov Vladimir , Holtz Mark , Temkin Henryk 
Published: April 2011

AbstractWe report the results of two studies of the growth and physical properties of AlGaN-based short-period superlattices (SPSLs), each aimed at improving light emission. In the first experiment, we grow structures on bulk AlN substrates. We observe ∼ 3 times higher luminescence efficiency than identically grown structures on sapphire. In the second experiment, we grow structures on sapphire while controlling the growth mode. We observe a significant improvement in the room temperature cathodoluminescence efficiency (at least by factor of 10) of AlGaN quantum wells when the 3D growth mode is induced by reduced flux of ammonia over identically prepared structures grown in the 2D mode.
Stress and Microstructure Evolution in Compositionally Graded Al1-xGaxN Buffer Layers for GaN Growth on Si
Authors: Weng Xiaojun , Raghavan Srinivasan , Dickey Elizabeth C , Redwing Joan M 
Published: April 2011

AbstractWe have studied the evolution of stress and microstructure of compositionally graded Al1-xGaxN (0 ≤ x ≤1) buffer layers on (111) Si substrates with varying thicknesses. In-situ stress measurements reveal a tensile-to-compressive stress transition that occurs near the half-thickness in each buffer layer. Cross-sectional transmission electron microscopy (TEM) shows a significant reduction in threading dislocation (TD) density in the top half of the buffer layer, suggesting that the compressive stress enhances the threading dislocation annihilation. The composition of the buffer layers varies linearly with thickness, as determined by X-ray energy dispersive spectrometry (XEDS). The composition grading-induced compressive stress offsets the tensile stress introduced by microstructure evolution, thus yielding a tensile-to-compressive stress transition at x ≈ 0.5.
Scanning Tunneling Microscopy Study of Cr-doped GaN Surface Grown by RF Plasma Molecular Beam Epitaxy
Authors: Haider Muhammad B. , Yang Rong , Al-Brithen Hamad , Constantin Costel , Smith Arthur R. , Caruntu Gabriel , O'Connor Charles J 
Published: April 2011

AbstractCr doped GaN was grown by rf N-plasma molecular beam epitaxy on sapphire(0001) at a sample temperature of 700 °C. Cr/Ga flux ratio was set to a value from 5% to 20%. Subsequently, scanning tunneling microscopy was performed on these surfaces. Cr incorporates on the GaN surface at 700 °C at a Cr concentration of 5% and less. By increasing the Cr/Ga flux ratio to 20% in CrGaN, linear nano structures were formed on the surface, which were not observed on the bare GaN surface. The RHEED and STM studies reveal that Cr atoms form 3×3 reconstruction when 0.1 ML of Cr was deposited at room temperature on 1×1 adlayer of Ga on GaN(000-1). Cr substitutes Ga on the surface when deposited at 700 °C on the MBE grown GaN(000-1) surface for all the experiments which we have performed provided the Cr concentration is low (∼5%).
High Power AlGaN/GaN Schottky Barrier Diode with 1000 V Operation
Authors: Yoshida Seikoh , Ikeda Nariaki , Li Jiang , Wada Takahiro , Kambayashi Hiroshi , Takehara Hironari 
Published: April 2011

AbstractWe investigated an AlGaN/GaN Schottky barrier diode (SBD) with a field plate structure for a high breakdown voltage. The AlGaN/GaN heterostructure was grown by MOCVD. The AlGaN buffer was grown on the Si (111) substrate and Al0.25Ga0.75N (25 nm)/ GaN (1000 nm) was grown on the buffer layer. The AlGaN/GaN heterostructure without any crack was obtained. After that, a Schottky barrier diode was fabricated using an AlGaN/GaN heterostructure. In order to obtain a high breakdown voltage, a gate field plate structure was used. SiO2 was formed on the AlGaN layer using a plasma chemical vapor deposition. The Schottky electrode of Ni/Au was partially deposited on the SiO2 film towards the ohmic region. The length of field plate structure was also changed to investigate the effect. Ti/Al-silicide was used for an ohmic electrode of SBD. The contact resistance of ohmic electrodes was 8E-6 ohmcm2.The current-voltage characteristics of an AlGaN/GaN SBD were measured. The reverse breakdown voltage of the diode was also over 1000 V and the reverse leakage current was below 1.5E-6 A/mm.
Influence of Nitrogen Species on InN Grown by PAMBE
Authors: Anderson P. A. , Kinsey R. J. , Kendrick C. E. , Farrel I. , Carder D. , Reeves R. J. , Durbin S. M. 
Published: April 2011

AbstractActive nitrogen species produced by an Oxford Applied Research HD-25 plasma source have been monitored by optical emission spectroscopy and quadrapole mass spectroscopy. Both techniques confirmed that at higher RF powers and lower flow rates the efficiency of atomic nitrogen production increased; emission spectroscopy confirmed that this was at the expense of active molecular nitrogen (N2*). InN films grown on (0001) sapphire/GaN with higher relative molecular content were found to have lower carrier concentrations than the corresponding films grown with higher atomic content. However, electrical properties of films grown on (111) YSZ showed insensitivity to the active nitrogen content. Etching experiments revealed that films grown on sapphire/GaN were nitrogen-polar, while films grown on YSZ were In-polar, suggesting that film polarity can greatly influence the effect active species have on growth. Lattice relaxation, as measured by reflection high-energy electron diffraction, revealed that the N-polar films grown under high relative molecular flux relaxed fully after ∼60 nm of growth, while the corresponding In-polar film relaxed fully within the first several nm of growth.
Carrier Recombination, Relaxation, and Transport Dynamics in InN
Authors: Chen Fei , Cartwright Alexander N , Lu Hai , Schaff William J 
Published: April 2011

AbstractKnowledge of the carrier recombination, relaxation, and transport processes in InN materials is essential for determining the applicability of this material system in photonic and electronic applications. In this article, we provide a review of time-resolved spectroscopy experimental techniques and our recent results using these techniques to measure transient processes in InN. Specifically, subpicosecond differential transmission experiments were used to determine the carrier recombination lifetime and the carrier thermalization time of InN. In those experiments, we observed a fast initial hot carrier cooling followed by a slower recombination process. At short times after pulsed excitation, modeling of the observed relaxation suggests that the dominant energy relaxation process is longitudinal optical phonon scattering modified by a strong hot phonon effect at room temperature. An inverse proportionality between the carrier lifetime and the free electron concentration was found. This suggests that donor-like defects or impurities may stimulate the formation of non-radiative recombination centers. Furthermore, we report the measurements of in-plane carrier transport and hole mobility of an InN epilayer by time-resolved transient grating spectroscopy using subpicosecond pulses at 800 nm and ∼1900 nm for grating writing and probing, respectively. The ambipolar diffusion coefficient Da = 2.0 cm2/s and hole mobility µh = 39 cm2/Vs at 300 K near the InN surface were determined by monitoring the transient grating kinetics at various grating periods.
Electron Transport Properties of InN
Authors: Jones Rebecca E. , van Genuchten Henricus C. M. , Li Sonny X. , Hsu Leon , Yu Kin Man , Walukiewicz Wladek , Ager III Joel W. , Haller Eugene E. , Lu Hai , Schaff William J. 
Published: April 2011

AbstractHigh-energy particle irradiation has been used to control the free electron concentration and electron mobility in InN by introducing native point defects that act as donors. A direct comparison between theoretical calculations and the experimental electron mobility suggests that scattering by triply-charged donor defects limits the mobility in irradiated samples across the entire range of electron concentrations studied. Thermal annealing of irradiated films in the temperature range 425°C to 475°C results in large increases in the electron mobility that approach the values predicted for singly-ionized donor defect scattering. It is suggested that the radiation-induced donor defects are stable, singly-charged nitrogen vacancies, and triply-charged, relaxed indium vacancy complexes that are removed by the annealing.
Fe-Centers in GaN as Candidates for Spintronics Applications
Authors: Malguth Enno , Hoffmann Axel , Phillips Matthew , Gehlhoff Wolfgang 
Published: April 2011

AbstractThe potential use of Fe doped GaN for spintronics applications requires a complete understanding of the electronic structure of Fe in all of its charge states. To address these issues, a set of 500 µm thick freestanding HVPE grown GaN:Fe crystals with different Fe-concentration levels ranging from 5×1017 to 2×1020 was studied by means of photoluminescence, photoluminescence excitation (PLE) and Fourier transform infrared (FTIR) transmission experiments. The Fe3+/2+ charge transfer (CT) level was determined to be at 2.86 ± 0.01 eV above the valence band maximum considerably lower than the previously reported value of 3.17 ± 0.10 eV. A bound state of the form (Fe2+, hVB) with a binding energy of 50 ± 10 meV has been established as an excited state of Fe3+. FTIR transmission measurements revealed an internal (5E-5T2) transition of Fe2+ around 400 eV which, until now, was believed to be degenerate with the conduction band. Consequently, a second CT band was detected in PLE spectra.
Characterization of a-plane AlGaN/GaN heterostructure grown on r-plane sapphire substrate
Authors: Iwaya Motoaki , Okadome Yoshizane , Tsuchiya Yosuke , Iida Daisuke , Miura Aya , Furukawa Hiroko , Honshio Akira , Miyake Yasuto , Kamiyama Satoshi , Amano Hiroshi , Akasaki Isamu 
Published: April 2011

AbstractThe anisotropically biaxial strain in a-plane AlGaN on GaN is investigated by X-ray diffraction analysis of the heterostructure of AlGaN and GaN grown on r-plane sapphire. The AlGaN layer with a low AlN molar fraction or small thickness is coherently grown on the GaN layer both along the m-axis and c-axis. An increase in AlN molar fraction or thickness in AlGaN, results in a slight relaxation of AlGaN only in one direction due to tensile stress along the c-axis, which is caused by the underlying GaN layer during the growth. The cause of the relaxation of AlGaN in one direction is thought to be a large anisotropically biaxial stress.
Reliability and degradation modes of 280 nm deep UV LEDs on sapphire
Authors: Gong Zheng , Chhajed Sameer , Gaevski Mikhail , Sun Wenhong , Advivarahan Vinod , Shatalov Maxim , Khan M. Asif 
Published: April 2011

AbstractIn this paper, we report a study of the degradation of AlGaN-based 280 nm LEDs, which were grown on sapphire substrates using migration-enhanced metalorganic chemical vapor deposition process (MEMOCVD). Electroluminescence (EL), atomic force microscopy (AFM), cathodoluminescence (CL), and scanning electron microscopy (SEM) observations showed that the degradation of deep UV LEDs generally fell into two categories: catastrophic degradation and gradual degradation. The catastrophic degradation was found to be mostly caused by the non-uniformity of surface morphology. The gradual power reduction had two characteristic time constants indicating two possible degradation mechanisms as found from temperature and bias dependent LED power degradation measurements. The faster time constant was bias dependent and virtually constant with temperature whereas the second time constant (slower) varied exponentially with junction temperature. For this temperature dependent part, the activation energies of degradation were determined to be 0.23 eV and 0.27 eV under injected current density of 100 A/cm2 and 200 A/cm2 respectively.
Morphological study of InN films and nanorods grown by H-MOVPE
Authors: Park Hyun Jong , Kang Sang Won , Kryliouk Olga , Anderson Tim 
Published: April 2011

AbstractHydride-Metalorganic Vapor Phase Epitaxy (H-MOVPE) was used to grow a series of films on c-Al2O3 substrates. Depending on the growth temperature and HCl/TMIn molar ratio, InN deposited as a continuous film or a collection of micro or nanorods, or no InN growth was observed. A chemical equilibrium analysis of the In-N-H-Cl system predicts both InN growth and etching regimes with the nanorod growth observed near the growth-etching transition. All InN rod structures demonstrated well faceted hexagonal structure with a near random orientation of the rods, while the films were polycrystalline.
Study of GaN Light-Emitting Diodes Obtained by Laser-Assisted Debonding
Authors: Chan C. P. , Yue T. M. , Surya C. , Ng A. M. C. , Djurišić A. B. , Liu C. K. , Li M. 
Published: April 2011

AbstractWe report experimental investigation of laser-assisted debonding of GaN-based light emitting diodes (LEDs) grown by metalorganic chemical vapor deposition (MOCVD) on sapphire substrates. The device was photo-electrochemically (PEC) etched to form hexagonal pyramid hillocks on the debonded surface. The luminous intensity of the debonded and roughened LEDs increased by 60% when compared to the LEDs on sapphire. This increase is attributed to the enhancement in photon extraction efficiency.
Role of deep levels in DC current aging of GaN/InGaN Light-Emitting Diodes studied by Capacitance and Photocurrent Spectroscopy
Authors: Castaldini Antonio , Cavallini Anna , Rigutti Lorenzo , Meneghini Matteo , Levada Simone , Meneghesso Gaudenzio , Zanoni Enrico , Härle Volker , Zahner Thomas , Zehnder Ulrich 
Published: April 2011

AbstractWe present a combined Capacitance-Voltage (C-V), Deep Level Transient Spectroscopy (DLTS) and Photocurrent (PC) study of short-term instabilities of InGaN/GaN LEDs submitted to forward current aging tests at room temperature. C-V profiles detect changes consisting in apparent doping and/or charge concentration increase within the quantum wells. This increase is correlated to dramatic modifications in the DLTS spectrum when the reverse bias and filling pulse are properly adjusted in order to probe the quantum well region. The new distribution of the electronic levels detected by DLTS could explain the observed decrease in the light emission efficiency [1,2] of the device, as the deep levels generated during the stress may provide alternative recombination paths for free carriers. The photocurrent spectra do not change in shape during stress, although their amplitude slightly decreases. This is related to a decrease of the device yield, in this photodetector configuration, with increasing aging time. Thus, we can suggest that the introduction of new defect levels in the bulk material lowers the free carrier mobility.
Double-Ion-Implanted GaN MESFETs with Extremely Low Source/Drain Resistance
Authors: Nomoto Kazuki , Ito Nobuyuki , Tajima Taku , Kasai Takeshi , Mishima Tomoyoshi , Inada Taroh , Satoh Masataka , Nakamura Tohru 
Published: April 2011

AbstractIncorporation of Si ion implantation to GaN metal semiconductor field effect transistor (MESFET) processing has been demonstrated. The channel and source/drain regions formed using Si ion implantation into undoped GaN on sapphire substrate. In comparison with the conventional devices without ion implanted source/drain structures, the ion implanted devices showed excellent device performance. On-state resistance reduces from 210 Ω-mm to 105 Ω-mm. Saturation drain current and maximum transconductance increase from 36 mA/mm to 78 mA/mm and from 3.8 mS/mm to 10 mS/mm, respectively.
Fabrication and device characteristics of bulk GaN-based Schottky diodes
Authors: Zhou Yi , Wang Dake , Ahyi Claude , Tin Chin-Che , Williams John , Park Minseo , Williams N. Mark , Hanser Andrew 
Published: April 2011

AbstractIn this investigation, Schottky diodes with different device sizes (150μm, 420μm and 700μm) were fabricated on the Ga-face of a free-standing n--GaN wafer produced by Kyma Technologies, Inc. Full area back side ohmic contact was prepared on the N-face of the bulk GaN using Ti/Al. Without any edge-termination scheme, a relatively high reverse breakdown voltage of 240V was achieved. The reverse breakdown voltage decreases as the device size increases. The forward turn-on voltage was as low as 2.4V at room temperature for the 150μm diameter Schottky diodes. The best on-state resistance was 7.56 mΩcm2 for diodes with VB=240V, producing a figure-of-merit (VB2/RON) of 7.6 MWcm-2. The Schottky diode also showed an extremely short reverse recovery time (< 20 ns) switching from forward bias to reverse bias.
Anti-diffusion barriers for gold-based metallization to GaN
Authors: Piotrowska Anna , Kaminska Eliana , Guziewicz Marek , Dynowska Elzbieta , Stonert Anna , Turos Andrzej , Figge Stephan , Kröger Roland , Hommel Detlef 
Published: April 2011

AbstractWe propose a new metallization scheme to p-GaN, where thin-film transition metal nitrides have been applied to improve thermal stability of gold-based metallization. In this metallization scheme the Pd/Au bilayer was used to form low-resistivity ohmic contact to p-GaN, while Ta-Si-N, Ti-Si-N, and Ti-W-N anti-diffusion barriers were used to protect contact metallization from interaction with Au overlayer. We present the details of optimization of process parameters of barrier layer fabrication and show that Ta0.34Si0.25Ni0.41 and Ti0.26Si0.0.17Ni0.57 thin films fabricated by reactive magnetron sputtering show excellent barrier properties under high temperature stress.
Planarization of GaN by the Etch-Back Method
Authors: Williams Adrian , Moustakas T.D. 
Published: April 2011

AbstractThe planarization of GaN has been mainly addressed by chemo-mechanical polishing methods in the literature. Such techniques were found to be successful in planarizing the nitrogen polar (000-1) surface of GaN. However, planarization of the gallium polar (0001) surface presents a challenge due to its higher degree of chemical inertness. Moreover, studies on the planarization of the remaining crystal orientations remain a topic with sparse representation in the literature. In this paper, we report our planarization studies of GaN films using an etch-back technique. Photoresist is employed as the sacrificial layer and a chlorine inductively coupled plasma (ICP) used for etching. We demonstrate the planarization of rough C-plane and A-plane GaN films grown by hydride vapor phase epitaxy (HVPE). Specifically, an rms roughness of approximately 2.1nm and 4.1nm was realized after iterative etch-back for a representative C-plane and A-plane sample with initial rms roughness of 134nm and 414nm respectively.
GaN-based Light Emitting Diode with Transparent Nanoparticles-Embedded p-Ohmic Electrodes
Authors: Song June-O , Kang Hun , Nicol David , Ferguson Ian T , Hong Hyun-Gi , Seong Tae-Yeon 
Published: April 2011

AbstractOptoelectronics related to GaN-based semiconductors (i.e., InGaN, GaN, and AlGaN) are new technologies that have the potential to far exceed the energy efficiencies of incandescent and fluorescent lighting sources. Among the GaN-based optoelectronic devices like light emitting diode (LED) and laser diode (LD), the GaN-based LEDs are of interest for the next generation illumination because of the representative characteristics such as small, highly radiant, reliably long, and fast responding, compared with the existing general lighting systems.Achievement of high luminous intensity by flip-chip LED (FCLED) with Ag-metallic reflector or using top emitting LED (TELED) with highly transparent ITO contact is required to improve the external quantum efficiency (EQE) and light output of GaN-based LEDs. However, since the work function of Ag and ITO is lower than 5.0 eV, it is difficult to produce low-resistance p-ohmic electrode with Ag-metallic reflector or ITO only.In this study, in order to develop new ohmic contact materials having low contact resistance and high transmittance, transparent nanoparticles-embedded p-ohmic electrode, Mg-doped indium oxide (MIO) (3 nm)/indium tin oxide (ITO) (400 nm) ohmic contact for high brightness TELEDs for solid-state lighting, was suggested. The MIO/ITO contact become ohmic with specific contact resistances of 2.64 × 10-3 Ωcm2 and give transmittance higher than 94.6 % at a wavelength of 450 nm when annealed at 630 °C for 1 min in air. GaN-based LEDs fabricated with the annealed MIO/ITO p-contact layer give a forward-bias voltage of about 3.38 V at injection current of 20 mA. It is further shown that the output power of the LEDs with the MIO/ITO contact is enhanced by about 1.86 times at 20 mA as compared with that of LEDs with the conventional Ni/Au contact.
MgZnO Nanocrystallites: Photoluminescence and Phonon Properties
Authors: Morrison John L. , Chen Xiang-Bai , Huso Jesse , Hoeck Heather , Mitchell James , Bergman Leah , Zheleva Tsvetanka 
Published: April 2011

AbstractWe report on the ultraviolet photoluminescence (UV-PL), Raman and structural properties of wurtzite MgxZn1-xO nanopowders of average size ∼ 30 nm that were synthesized via the thermal decomposition method. For the studied composition range of, the room temperature UV-PL was found to be tuned by ∼ 0.24 eV towards the UV-spectral range, and the PL emission was established to be due to an excitonic-type recombination mechanism. The first-order LO Raman mode was found to exhibit a blueshift of ∼ 33 cm-1. The LO-mode of the nanopowders is discussed in terms of a mixed A1-E1 symmetry phonon known as a quasi-LO mode. The observed 30 cm-1 blueshift indicates that the E1 is the principle symmetry component in the Raman scattering of the MgxZn1-xO nanopowders.
Characteristics of a phosphorus-doped p-type ZnO film by MBE
Authors: Xiu Faxian , Yang Zheng , Leelaprasanna Mandalapu J. , Liu Jianlin 
Published: April 2011

AbstractA solid-source GaP effusion cell was used to provide phosphorus dopants to achieve p-type ZnO with molecular-beam epitaxy (MBE). Room temperature (RT) Hall-effect measurements reveal that phosphorus-doped ZnO has a strong p-type conduction with a hole concentration of 6.5×1018 cm-3 and a hole mobility of 9.0 cm2/V s. X-ray diffraction measurements show a preferential growth orientation along <11-20> by θ-2θ scan and a tilt of ZnO (11-20) plane relative to the substrate surface by rocking curve and reciprocal space map. Photoluminescence (PL) spectra at 8.5 K show a dominant acceptor-bound exciton emission at 3.319 eV. The acceptor energy level of the phosphorus dopant is calculated to be 0.18 eV above the valence band from PL spectra, which is consistent with the temperature dependence of PL measurements.