bluuebunny/crossref_metadata_2025_split huggingface dataset:
Annealing Time Dependence on 1.5μm Photoluminescence of Laser-Ablated β-FeSi2
Authors: Uekusa Shin-ichiro , Aoki Kunitoshi , Hossain Mohammad Zakir , Fukuda Tomohiro , Miura Noboru 
Published: April 2011

ABSTRACTWe prepared β-FeSi2 thin-films by using a Pulsed Laser Deposition (PLD) method and succeeded to observe photoluminescence (PL) around 1.5 μm corresponding to β-FeSi2 band from the long-time and high-temperature annealed β-FeSi2 thin-films. The β-FeSi2 thin-films were ablated on Si(111) substrates heated at 550°C. After ablation, long-time and high-temperature thermal annealing was performed in order to improve the crystal-quality. Annealing times were 5, 10, 20 and 40 hrs, and annealing temperature was kept at 900 °C. Crystallinity was evaluated by an X-ray diffraction (XRD) measurement. We have observed eminent improvement on crystal-quality of β-FeSi2 thin-films. Annealed samples show (220) or (202) X-ray diffraction signals of β-FeSi2 and the full width at half maximum (FWHM) of these peaks were 0.27° although the thickness of the samples decreased with annealing time. Thermal-diffusion of Si atoms was observed from substrate to thin-films. Fe atoms in the ablated thin-films also diffused into the substrate. The relationship between the thickness of β-FeSi2 thin-films and the thermal-diffusion were investigated with rutherford backscattering (RBS) measurement. Maximum photoluminescence intensity around 1.5 μm was observed from the thickest β-FeSi2 thin-film with only 5 hrs annealing.
Spectral and Temporal Resolution of THz Detectors based on Quantum Hall Devices with various Geometries
Authors: Kalugin Nikolai G. , Stellmach C. , Vasilyev Yu. , Hirsch A. , Hein G. , Sǎgol B. E. , Nachtwei G. 
Published: April 2011

ABSTRACTQuantum Hall (QH) systems can work as very sensitive THz detectors. In this work we report on the spectral and temporal resolution of the QH THz photodetectors with different geometries. The spectral resolution of THz QH detectors is of the order of 1-3 meV depending on bias conditions. The temporal resolution of QH detectors depends on the device geometry. For Corbino-shaped detectors we have demonstrated the devices with response times from 10 ns to over 200 ns.
Directional Growth of Si Nanowires on Insulating Films by Electric-Field-Assisted Metal-Induced Lateral Crystallization
Authors: Kanno Hiroshi , Kenjo Atsushi , Sadoh Taizoh , Miyao Masanobu 
Published: April 2011

ABSTRACTMetal-induced lateral crystallization of amorphous Si has been investigated under a wide range of electric fields (0-4000 V/cm). In the low field region (<100 V/cm), lateral growth velocity at the cathode side was enhanced by applying an electric field. This achieved formation of poly-Si with a large area (∼50 μm) during low-temperature annealing (525°C, 25 h). When the electric field exceeded 100 V/cm, the lateral growth velocity decreased with increasing the electric field strength. Under the extremely high electric field (>2000 V/cm), directional growth aligned to the electric field was observed. This new findings will be a powerful tool to achieve new poly-Si with highly controlled structures.
UV photoconductors based on Ga-doped ZnO films
Authors: Mandalapu Leelaprasanna J. , Xiu Faxian , Yang Zheng , Liu Jianlin 
Published: April 2011

ABSTRACTGa-doped n-type ZnO films were grown by molecular-beam epitaxy (MBE) on R-plane sapphire substrates. Material characterizations such as photoluminescence (PL), X-ray diffraction (XRD), secondary ion mass spectroscopy (SIMS) and Hall measurements were carried out to characterize the optical, structural, and electrical properties of the film. Photoconductor devices for ultraviolet (UV) light detection were fabricated by depositing Al (250 nm)/Ti (20 nm) ohmic metal contacts. Linear characteristics were obtained from current-voltage (I-V) measurements that showed response to UV and visible illumination. Voltage dependent photocurrent (PC) spectra and responsivity spectrum were obtained to characterize the detection capability of the device in the UV region.
Nonmagnetic Doping Effect on the Magneto-Transport Properties of Mn Doped ZnO Dilute Magnetic Semiconductors
Authors: Mundada Govind , Manchiraju Srikanth , Kehl Ted , Pulugam Sandhya , Patel Rishi J. , Kahol Pawan , Ghosh Kartik 
Published: April 2011

ABSTRACTIn this paper we report non magnetic elements (Al and Cu) doping effect on the structural and magneto-transport properties of Zn0.85Mn0.15O dilute magnetic semiconductors. Thin films of undoped Zn0.85Mn0.15O (ZnMnO), Al doped Zn0.80Al0.05Mn0.15O (ZnMnAlO), and Cu doped Zn0.85Cu0.05Mn0.15O (ZnMnCuO) were grown on sapphire single crystals using pulse laser deposition technique. X-Ray Diffraction and Raman Spectra confirm the epitaxial growth with a strong orientation along the c-axis. Scanning Electron Microscopy and Atomic Force Microscopy reveals surface microstructure of all the films. Magneto transport properties quantify the carrier concentrations and mobilities at room temperature in all the films.
Growth and Properties of Lattice Matched GaAsSbN Epilayer on GaAs for Solar Cell Applications
Authors: Bharatan Sudhakar , Iyer Shanthi , Matney Kevin , Collis Ward J. , Nunna Kalyan , Li Jia , Wu Liangjin , McGuire Kristopher , McNeil Laurie E. 
Published: April 2011

ABSTRACTIn this work, the growth and characterization of GaAsSbN epilayers nearly lattice matched to GaAs, grown in an elemental solid source molecular beam epitaxy (MBE) system with a RF plasma nitrogen source, are discussed. The Sb and N compositions of the nearly lattice matched layers are 2.6% and 6.8%, respectively, as determined by high resolution x-ray diffraction (HRXRD) and secondary ion mass spectroscopy (SIMS) analysis. The layers are found to be fully strained as evidenced by the presence of Pendellosung fringes on the x-ray diffraction spectra.Effects of in-situ and ex-situ annealing on the low temperature photoluminescence (PL) characteristics are discussed. The 10 K PL peak energy of 1 eV with a FWHM of 18 meV has been achieved on ex-situ annealed samples in N ambient. The temperature dependence of PL peak energy exhibits “S-shaped” behavior in the low temperature regime, indicative of the presence of localized excitons. Raman spectroscopy analysis has been carried out to determine the local structural changes on annealing.
White-light Emitting ZnO-SiO2 Nanocomposite Thin Films Prepared by Sputtering Method
Authors: Peng Yu-Yun , Hsieh Tsung-Eong , Hsu Chia-Hung 
Published: April 2011

ABSTRACTZnO-SiO2 nanocomposite thin films were prepared using RF sputtering method without substrate heating. The photoluminance (PL) measurements showed that the ZnO-SiO2 nanocomposite thin films are able to emit white light consisting of violet, blue, and green-yellow band emissions. The blue emission was attributed to the large amount of ZnO/SiO2 interfaces, which enlarges the depletion layer width and then enhances the related transition. Further analyses indicated that the defect structure of samples could be manipulated by the amount and distribution of ZnO nanoparticles in SiO2 matrix to yield distinct luminescence property.
Minority Carrier Lifetime Measurement in Germanium on Silicon Heterostructures for Optoelectronic Applications
Authors: Sheng Josephine J. , Carroll Malcolm S. 
Published: April 2011

ABSTRACTDemand for low cost and high density near infrared (NIR) detection has motivated the development and use of germanium on silicon (Ge/Si) heterostructures to extend the optoelectronic application of Si technology. Ge/Si structures are currently being considered for NIR p/n detectors that can be integrated with Si CMOS [1]. Various research demonstrations of integrated Ge/Si diodes with CMOS have been made including using sputtered poly-Ge to form Ge/Si photodiodes after the CMOS transistors were complete. Poly-crystalline germanium (poly-Ge) may be formed by various methods including the use of plasma enhanced chemical vapor deposition. In this work, the formation of poly-Ge/Si heterostructures by inductively coupled plasma enhanced chemical vapor deposition (ICP-CVD) is examined as an alternative method to integrate poly-Ge into a CMOS process flow. In this work, 25 nm poly-Ge on Si heterostructures are formed by either recrystallization of ICP-CVD hydrogenated amorphous germanium (α-Ge:H) or direct deposition of ICP-CVD poly-Ge. A rapid measure of the suitability for detectors of the different poly-Ge films is the minority carrier recombination lifetime, which can affect dark current, quantum efficiency and overall detector detectivity. Recombination lifetimes were measured, therefore, in α-Ge:H that was recrystallized using rapid thermal annealing between 400 – 1050 °C in nitrogen ambient. Lifetimes were measured using a non-contact inductively coupled photo-conductance setup and an effective surface recombination velocity is subsequently extracted for each Ge/Si heterostructure that describes the integrated recombination in the Ge layer and at the Ge/Si interface, which separates the Ge contribution from recombination in the bulk silicon and at the silicon surface. The effective recombination velocities for the 25 nm Ge layers are found to be ∼103−104 cm/s.
Structural, Optical, and Magnetic Behavior of in-situ Doped, MOCVD-Grown Ga1-xMnxN Epilayers and Heterostructures
Authors: Li Nola , Fenwick William E. , Strassburg Martin , Asghar Ali , Gupta Shalini , Kang Hun , Li Nola , Summers Christopher , Ferguson Ian T. 
Published: April 2011

AbstractDilute magnetic semiconductors (DMS) show promise as materials that can exhibit ferromagnetism at room temperature (RT). However, the nature of ferromagnetism in this material system must be well understood in order to allow intelligent design of RT spintronic devices. This work investigates the magnetic properties of the as-grown films and the effect of Mn incorporation on crystal integrity and device performance. Ga1-xMnxN films were grown by MOCVD on c-plane sapphire substrates with varying thickness and Mn concentration. Homogenous Mn incorporation throughout the films was verified with Secondary Ion MassSpectroscopy (SIMS), and no macroscopic second phases (MnxNy) were detected using X-ray diffraction (XRD). Superior crystalline quality in the MOCVD-grown films relative to Mn-implanted GaN epilayers was confirmed via Raman spectroscopy. Vibrating sample magnetometry measurements showed an apparent room temperature ferromagnetic hysteresis in the as-grown epiayers. Similarly, a marked decrease in the magnetization was observed with annealing and silicon doping, as well as in post-growth annealed Mg-codoped samples. The observed decrease in muB per Mn with increasing Mn concentration is explained by Raman spectroscopy results, which show a decrease in long-range lattice ordering and an increase in nitrogen vacancy concentration with increasing Mn concentration. Magnetic and electron-spin paramagnetic resonance (EPR) data also show that the position of the Fermi level relative to the Mn2+/3+ level is the determining factor in magnetization. Light emitting diodes (LEDs) containing a Mn-doped active region have also been produced. Devices were fabricated with different Mn-doped active layer thicknesses, and I-V characteristics show that the devices become more resistive as thickness of the Mn-doped active layer increases. The magnetic and structural properties observed in this work will be used in conjunction with characteristics and magneto-optical of the Mn-containing devices to discuss the theoretical models of ferromagnetism in Ga1-xMnxN
InN Nano Rods and Epitaxial Layers Grown by HVPE on Sapphire Substrates and GaN, AlGaN, AlN Templates
Authors: Syrkin Alexander , Usikov Alexander , Soukhoveev Vitali , Kovalenkov Oleg , Ivantsov Vladimir , Dmitriev Vladimir , Collins Charless , Readinger Eric , Shmidt Natalia , Nikishin Sergey , Kuryatkov Vladimir , Song Daoying , Holtz Mark 
Published: April 2011

AbstractThis paper contains results on InN growth by Hydride Vapor Phase Epitaxy (HVPE) on various substrates including sapphire, GaN/sapphire, AlGaN/sapphire, and AlN/sapphire templates. The growth processes were carried out at atmospheric pressure in a hot wall reactor in the temperature range from 500 to 650°C. Arrays of nano-crystalline InN rods with various shapes were grown directly on sapphire substrates. Continuous InN layers were grown on GaN/sapphire, AlN/sapphire and AlGaN/sapphire template substrates. X-ray diffraction rocking curves for the (00.2) InN reflection exhibit the full width at half maximum (FWHM) as narrow as 0.075 deg. for the nano-rods and 0.128 deg. for the continuous layers grown on GaN/sapphire templates.
Analysis of high-power packages for white-light-emitting diode lamps with remote phosphor
Authors: Luo Hong , Kim Jong Kyu , Xi Yangang , Schubert E. Fred , Cho Jaehee , Sone Cheolsoo , Park Yongjo 
Published: April 2011

AbstractAn optimized packaging configuration for high-power white-light-emitting diode (LED) lamps that employs a diffuse reflector cup, a remote phosphor and a hemi-spherically-shaped encapsulation is presented. Ray tracing simulations for this configuration show that the phosphor efficiency can be enhanced by up to 50% over conventional packages. It is experimentally shown that dichromatic LED lamps with remote phosphor and diffuse reflector cup configuration have higher phosphor efficiency by 15.4% for blue-pumped yellow phosphor and by 27% for ultraviolet-pumped blue phosphor over conventional packages. Those improvements are attributed to reduced absorption of the phosphorescence by the LED chip and the reduction of deterministic optical modes trapped inside the encapsulant.
Fast High-Density Low-Pressure Plasma Synthesis of GaN Nanocrystals
Authors: Anthony Rebecca Joy , Thimsen Elijah , Johnson Joe , Campbell Stephen A , Kortshagen Uwe 
Published: April 2011

AbstractGallium Nitride is of interest due to its direct bandgap, which allows for efficient emission in the near-UV range. Bulk GaN is already in use in solid-state devices that exploit its emissive properties, however, the promise of GaN nanocrystals as tunable emitters for use in light-emitting devices and lasers has led to the recent exploration of nanocrystalline GaN synthesis routes. Here we discuss the use of nonthermal plasmas for the synthesis of nanocrystalline pow-ders of GaN. The particles were examined using transmission electron microscopy and x-ray photoelectron spectroscopy.
Opto-electronic Simulation of GaN Nanowire Lasers
Authors: Chen Liang , Towe Elias 
Published: April 2011

AbstractA self-consistent, coupled opto-electronic simulation for studying GaN nanowire lasers is presented. The model solves, simultaneously and self-consistently, the carrier transport equations and the photon rate equations. The basic physical model takes into account both bulk and surface dark recombinations, stimulated emission, the anisotropic optical gain typical of the Wurtzite GaN structure, the modified spontaneous emission, and its coupling into the lasing modes by microcavity effects. The model further incorporates band gap shrinkage effects due to band renormalization and the effects of multiple lateral and longitudinal lasing and non-lasing optical modes.
Analysis of the Quantum Efficiency of GaInN/GaN Light Emitting Diodes in the Range of 390 - 580 nm
Authors: Zhao Wei , Li Yufeng , Xia Yong , Zhu Mingwei , Detchprohm Theeradetch , Schubert E. Fred , Wetzel Christian 
Published: April 2011

AbstractIn an attempt to identify the performance limiting factors of green GaInN/GaN light emitting diodes (LEDs) we analyze a large number of LED dies fabricated from over 160 epitaxy runs covering the wavelength range from 390 – 580 nm on a quantitative scale of the emission power. As a function of drive current, we analyze the external quantum efficiency (EQE) with particular emphasis on the low current range. We observe three very distinct populations of EQE behaviors. We find that the EQE maximum value has a strong correlation with the forward current in this point, while it has weak correspondences with both, the forward voltage in this point, and the dominant wavelength at 20 mA. The very good linear relationship between the forward voltage in green LED dies at 1 mA and at 20 mA is also observed. All those characteristics are meaningful traits to ultimately converge to a physical electronic transport and bandstructure model for the next step enhancement of green and deep green GaInN/GaN LED performance.
Application of Aluminum Nitride Thin Film for Micromachined Ultrasonic Transducers
Authors: Wang Qianghua , Xu Jianzeng , Huang Changhe , Auner Gregory W 
Published: April 2011

AbstractThis paper reports the fabrication and characterization of micromachined ultrasonic transducers (MUT) based on piezoelectric aluminum nitride (AlN) thin films. The MUT device is composed of an Al/AlN/Al sandwiched structure overlaid on top of a silicon (Si) diaphragm. X-ray diffraction (XRD) scan shows that highly c-axis oriented AlN (002) thin films have been grown on Al/Si(100) substrates. Electrical impedance of the MUT devices is analyzed as a function of frequency. The fundamental resonant frequencies of the devices are found in the range of 65-70 kHz, which are in approximation to the theoretical calculation. The effective coupling factors of the devices are also derived as 0.18.
Mechanism of Current Leakage in Ni Schottky Diodes on Cubic GaN and AlxGa1-xN Epilayers
Authors: As Donat J. , Potthast Stefan , Fernandez Jara , Lischka Klaus , Nagasawa Hiroyuki , Abe Masayuki 
Published: April 2011

AbstractNi Schottky-diodes (SDs) 300 μm in diameter were fabricated by thermal evaporation using contact lithography on cubic GaN and AlxGa1-xN epilayers. Phase-pure cubic GaN and c-Al0.3Ga0.7N/GaN structures were grown by plasma assisted molecular beam epitaxy (MBE) on 200 µm thick free-standing 3C-SiC (100) substrates. The quality of the cubic group III-nitride epilayers was checked by high resolution X-ray diffractometry, atomic force microscopy and photoluminescence at room temperature and at 2 K. Large deviations from the thermionic emission transport were observed in the current voltage (I-V) behavior of these SDs. Detailed analysis of the I-V characteristics at 300 K and at low temperature showed that a thin surface barrier is formed at the Ni semiconductor interface. Thermal annealing in air at 200°C alters the composition of this thin surface barrier and reduces the leakage current by three orders of magnitude. The doping density dependence of breakdown voltages derived from the reverse breakdown voltage characteristics of c-GaN SDs is in good agreement with theoretically calculated values and follows the expected trend. From these experimental data a blocking voltage of higher than 600V is extrapolated for c-GaN films with a doping level of ND = 5×1015 cm-3.
Simulation of Self-Heating and Temperature Effect in GaN-based Metal-Semiconductor Field-Effect Transistor
Authors: Turin Valentin O , Balandin Alexander 
Published: April 2011

AbstractTwo-dimensional electro-thermal simulations of GaN-based metal-semiconductor field-effect transistor are performed in the framework of the drift-diffusion model. The dependence of the hot spot temperature in transistors with many gates on the gate-to-gate pitch is studied. The case of SiC substrate is compared to the case of sapphire substrate. The ambient temperature effect on transistor performance is simulated. The specific of a thermal breakdown in GaN-based devices is discussed. The results obtained can be useful for the optimization of the thermal design for field-effect transistors.
Electrical domains and sub-millimeter signal generation in AlGaN/GaN superlattices
Authors: Gordion Irina , Manasson Alexander , Litvinov Vladimir 
Published: April 2011

AbstractThe paper discusses the feasibility of a terahertz-signal source made of AlGaN/GaN superlattice. Negative differential conductivity, electrical domain formation, current oscillations, and power efficiency of a perspective source are described. We relate the superlattice geometry and conduction band profile, distorted by polarization fields, to the oscillation frequency and power efficiency of the device. We also determine the optimal Al content, superlattice period, and the parameters of external circuit that favor sub-millimeter wave generation.
Design and Development of MBE Grown AlGaN/ GaN HEMT Devices on SiC Substrates for RF Applications
Authors: Sood Ashok K , Singh Rajwinder , Puri Yash R , Clarke Frederick W , Dabiran Amir , Chow Peter , Deng Jie , Hwang James C.M. 
Published: April 2011

AbstractGaN /AlGaN transistors are being developed for a variety of RF electronic and high temperature electronics applications that will replace GaAs and Silicon based devices and amplifiers for commercial and military applications. In this paper, we present GaN/AlGaN based HEMT device architectures on SiC substrates with simulation and modeling results. The HEMT epitaxial layers were grown using RF Plasma Assisted MBE Technique. This approach has demonstrated very uniform epitaxial layers. The key to high performance HEMTs is the ability to grow high quality (Al)GaN buffer layers. Details of the electrical and optical characteristics of the HEMT wafers are presented. In addition, we will present results on an modified (ICP) etching technique that allows for low damage device processing and improved reliability.
Substrate influence on the high-temperature annealing behavior of GaN: Si vs sapphire
Authors: Pastor David , Cuscó Ramon , Artús Luis , Iborra Enrique , Jiménez Juan , Peiró Francisca , González-Díaz German , Calleja Enrique 
Published: April 2011

AbstractWe have studied the effects of rapid thermal annealing at 1300°C on GaN epilayers grown on AlN buffered Si(111) and on sapphire substrates. After annealing, the epilayers grown on Si display a stained surface. Scanning electron microscopy and optical confocal images revealed the presence of crater-shaped inhomogeneities that develop around protruding nuclei with tipically 50 micron diameter. Energy dispersive x-ray microanalysis yields a high concentration of Si in the crater regions as well as non-stoichiometric concentrations of Ga and N, with an excess of N.Micro-Raman spectra obtained within the crater region exhibit Raman peaks associated with Si3N4 but no trace of GaN modes, while focused ion beam milling of this region leads to the accumulation of metallic Ga in the etched area. These results suggest that a substantial migration of Si from the substrate takes place during the annealing, which severely alters the material in the crater regions. Such annealing effects, which are not observed in GaN grown on sapphire, constitute a severe drawback for a widespread use of Si(111) substrates when high-temperature processing is required.
Charge Profiling of the p-AlGaN Electron Blocking Layer in AlGaInN Light Emitting Diode Structures
Authors: Xia Yong , Li Yufeng , Zhao Wei , Zhu Mingwei , Detchprohm Theeradetch , Schubert E. Fred , Wetzel Christian 
Published: April 2011

AbstractCharacterization of operational AlGaInN heterostructure light emitting diodes (LEDs) is critical to their performance optimization and time-to-failure analysis. Typically, device performance data needs to be corroborated with structural information such as layer thicknesses, charge profiles, and the absolute location of the pn-junction. Here, non-destructive testing by capacitance-voltage profiling is being applied to AlGaInN LED structures. Within a large set of samples with different active layer geometry, we observe distinct layers of high mobile charge accumulation. We correlate those with layer thicknesses derived from an x-ray diffraction analysis of the corresponding epiwafers. In this way, we identify the charge maxima as the upper and lower interfaces of the p-type AlGaN electron blocking layer to the neighboring GaN layers. By means of this successful analysis, we now have the opportunity to monitor epi process performance and stability as well as device degradation progress quasi-continuously over the device lifetime in a non-destructive mode.