bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantum Dot Spectral Tuning of Multijunction III-V Solar Cells
Authors: Bailey Christopher , Hubbard Seth , Polly Stephen J , Forbes David V , Raffaelle Ryne P. 
Published: January 2010

AbstractImproving the production of photocurrent in the middle junction of a InGaP/Ga(In)As/Ge triple-junction solar cells (TJSC) can improve the overall conversion efficiency of cell. One possible method to improve the middle junction photocurrent is inserting a quantum dot (QD) superlattice (SL) into the stack. It has been predicted that QD-SL enhanced TJSCs have an efficiency ceiling of 47% under a one-sun AM0 illumination spectrum. Additionally, QD array enhanced GaAs cells have the added benefit of possible intermediate band effects, anisotropic absorption and enhanced radiation tolerance. Embedding InAs quantum dots (QDs) in a single junction GaAs solar cell can increase sub-GaAs bandgap photocurrent generation. This method has been shown to improve the short circuit current density (Jsc) of single junction cells under simulated 1 sun air mass zero (AM0) illumination. However, the increase in strain due to the InAs QD self-assembly may cause defects that reduce the minority carrier lifetime resulting in losses in the cell open circuit voltage (Voc) on the order of 300-500 mV. The introduction of strain compensation (SC) layers into the superlattice (SL) structure of a QD solar cell has previously been shown to improve the device performance, including the partial recovery of Voc. Strain compensation can be used effectively to balance the residual strain, impede dislocation formation, and improve the solar cell characteristics. The effect of GaP strain compensation on the solar cell electrical and material properties was investigated. High resolution X-ray diffraction (HRXRD) scans along the symmetric (004) Bragg peak show weak intensity and wide FWHM at the zero order SL peak (SL0) for non-SC samples. Optimum SC thickness was theoretically determined using a zero in plane stress method and experimentally verified using HRXRD. Optimal strain compensation was then used to increase the QD SL stacking from 5x to 10x and 20x. Use of SC resulted in shifting of the SL0 peak toward the substrate peak as well as reduced FWHM and improved SL peak definition. Kinematical diffraction modeling of the QD structures using numerical simulation indicated this peak shift resulted from reduced overall strain in the SL stack up to 5ML of SC. The material quality improvement in the SC QD solar cells was manifested in an improved spectral response and Jsc. The optoelectronic results for GaAs solar cells with QD SL’s demonstrate a strong dependence on GaP SC layer thickness. In addition, comparison of multi junction (MJ) solar cells which incorporate the SC QD SL’s demonstrate the utility of additional sub-GaAs bandgap current contribution as a tool for additional current-matching optimization in MJ solar cells.
Catastrophic Optical-damage in High-power, Broad-area Laser-diodes
Authors: Chin Aland K. , Bertaska Rick K. , Jaspan Martin A. , Flusberg Allen M. , Swartz Steve D. , Knapczyk Maciej T. , Smilanski Israel , Jacob Jonah H. 
Published: January 2010

AbstractA detailed description of the phenomenon of catastrophic optical-damage (COD) in short (380μm cavity-length), 12μm aperture, proton-bombarded, double-heterostructure laser-diodes with uncoated facets was first presented in 1974. In these devices, COD generally initiates at the facets due to high optical-power density and propagate along transverse-mode filaments. To achieve reliable operation at high optical-power, broad-area laser-diodes have evolved to long (several-millimeter cavity-length), wide-aperture (50-200μm), dielectric-defined, broadened-waveguide, separate-confinement, double-heterostructure, quantum-well laser-diodes with coated, passivated facets. COD in these devices involve both transverse modes and ring-cavity modes.
InGaN Laser Diode Degradation. Surface and Bulk Processes
Authors: Perlin Piotr , Marona Łucja , Wisniewski Przemek , Leszczynski Mike , Prystawko Pawel , Boćkowski Michał , Czernecki Robert , Makarowa Irina , Kowalski Bogdan , Suski Tadek 
Published: January 2010

AbstractWe discuss main degradation mechanisms present in nitride based laser diodes operating in 400-440 nm spectral range. We can clearly divide the aging processes into these occurring on the exposed facets of the device and into the bulk phenomena. Surface processes are predominantly connected with photochemical reactions on the laser mirrors and manifest by the formation of the carbon deposits. The nature of these photochemical reactions resembles very closely the mechanism known as Package Induced Failure observed previously in case of 980 nm laser diodes. Degradation involving bulk like effects is much less understood. The experimental results by other group are not sufficient for proposing an unambiguous model of the physical effects involved. In particular, it consists in observation related to dopants diffusion and recombination mechanisms. Magnesium diffusion from the p-type layers into the active layer was proposed as a possible degradation path. However, our study of SIMS profiles in the device subjected to over 8 000 h of electrical stress reveals no visible modification in the Mg profile. The same holds for the hydrogen spatial distribution thus substantially limiting candidates for the diffusion processes. Nevertheless, it seems that the diffusion mechanism is involved in bulk degradation. The claim is supported by two facts: well confirmed stability of the extended defects network in nitride emitters and characteristic square-root time-dependence of the degradation rate.
A Study of Degradation in High Power Multi-Mode InGaAs-AlGaAs Strained Quantum Well Lasers as Pump Lasers
Authors: Sin Yongkun , Presser Nathan , Ives Neil , Moss Steven C. 
Published: January 2010

AbstractDegradation processes in high power broad-area InGaAs-AlGaAs strained quantum well lasers were studied using electron beam-induced current (EBIC) techniques, time-resolved electroluminescence (TR-EL) techniques, and deep-level transient spectroscopy (DLTS). Accelerated lifetests of the broad-area lasers yielded catastrophic failures at the front facet and also in the bulk. EBIC was employed to study dark line defects generated in degraded lasers stressed under different test conditions. TR-EL was employed to study the intra-cavity intensity distribution in real time as devices were aged. DLTS was employed to study deep electron traps in both pristine and degraded laser diodes. Lastly, we present a possible scenario for the initiation of bulk degradation in the broad-area lasers.
Recombination-enhanced Dislocation Glides—The Current Status of Knowledge
Authors: Maeda Koji 
Published: January 2010

AbstractTo update the status of knowledge on the recombination-enhanced dislocation glides (REDG) in semiconductors, which is one of the causes of serious degradation in bipolar devices, research progress achieved for the last decade has been surveyed. Rather than presenting a complete review over a wide range of material systems, a particular attention has been paid to the REDG effect in 4H-SiC for which a lot of information has been accumulated owing to extensive studies. Although the REDG effect exhibits features that could be interpreted in terms of the phonon-kick mechanism, conclusive proof is still lacking.
Modifications of Defects Concentration Induced by Ammonia Flow Rate and its Effects on Gallium Nitride Grown by MOCVD
Authors: Sundaram Suresh , Ganesh Vattikondala , Prem Kumar Thirugnanam , Balaji Manavaimaran , Ganesan Vedachala Iyer , Baskar Krishnan 
Published: January 2010

AbstractOptical and schottky diode characteristics of unintentionally doped GaN films grown by MOCVD were reported. GaN epilayers were grown with different V/III ratio by varying the source ammonia (NH3) flowrate. It exhibit changes in the density of threading dislocations (TDs) and reduced carbon and oxygen impurity incorporation. The density of dislocations determined from hot-wet chemical etching and atomic force microscopy show that on decreasing the ammonia flowrate, threading dislocations decreases. Low energy positron beam was employed to study the Ga vacancies in the epilayers. S-parameter vs. positron beam energy curves clearly shows increase in SL on increasing the V/III ratio indicating that the point defects trapping positron increases. Corroborative HRXRD, Photoluminescence and Hall measurements confirm the reduction in trapping defects and threading edge dislocations with reducing V/III molar ratio. The effects of such variation of compensating centres and radiative centres as a function of MOCVD growth conditions on optical properties and schottky device characteristics like radiative decay lifetime, barrier height and reverse leakage current respectively were discussed.
Large Batch Etching of Gallium Nitride Using Inductively Coupled Plasma Tools as a Production Solution
Authors: Ren Zhong , Dineen Mark , Deng Ligang , Goodyear Andrew L. , Gunn Robert 
Published: January 2010

AbstractA highly effective technique for etching large batches of GaN wafers, by means of Inductively Coupled Plasma (ICP) tools, has been developed. A variety of 27 × 2 inch wafer batch processes have been investigated and etch rates in excess of 140nm/min with selectivity of 0.9:1 to photoresist (PR) has been achieved.Particularly, a special active spacer was designed and employed in the ICP system to control plasma profile during the processes. This technique was favourable for increasing etch rates and achieving good uniformities. Using this system a wafer-to-wafer batch uniformity of ±4% was realized.
A Comprehensive Approach to HEMT Reliability Testing
Authors: Cheney David , Gila Brent , Douglas Erica Ann , Ren Fan , Pearton S. 
Published: January 2010

AbstractReliability testing often manifests device weaknesses and failure mechanisms. As new materials and structures are developed, creative and different testing is often necessary to determine reliability. We are developing an in-house reliability test system that will provide the necessary testing flexibility of HEMT devices so researchers can pinpoint defects and vulnerabilities. Using commercial off-the-shelf (COTS) power supplies and data acquisition equipment, a custom control system allows for many different tests: DC and RF, temperature, step/stress/recovery, high-speed pulse, and optical pumping, as well as combinations and automated sequencing of these tests. This flexibility allows for the creation of new test types as failure mechanisms are understood. The initial station will provide for the simultaneous, independent testing of 16 devices. This paper outlines the system design and capabilities, the motivation for the system, and some results from different tests.
Reliability of High-Temperature Operation for GaN-Based OPAMP
Authors: Nomoto Kazuki , Hasegawa Kazuya , Satoh Masataka , Nakamura Tohru 
Published: January 2010

AbstractWe demonstrated electrical characteristics of operational amplifier (OPAMP) circuits fabricated by GaN/AlGaN/GaN HEMTs operating over 100 oC. GaN/AlGaN/GaN HEMTs, with the extremely low source resistance were fabricated by multiple ion implantation, precisely controlled ion-implanted (I/I) resistors and Schottky barrier diodes were integrated on the silicon substrate. The GaN cap layer on the AlGaN was grown to decrease the gate leakage current and current collapse for AlGaN/GaN HEMTs.
High Current Gain Triple Ion Implanted 4H-SiC BJT
Authors: Tajima Taku , Nakamura Tadashi , Watabe Yuki , Satoh Masataka , Nakamura Tohru 
Published: January 2010

AbstractWe investigated triple ion implanted 4H-SiC BJT with etched extrinsic base regions. To remove the defects induced by ion implantation between emitter and base regions, the characteristics of triple ion implanted 4H-SiC BJT were significantly improved. Maximum common current gain was improved from 1.7 to 7.5.
Temperature Dependent Optical Band Gap Measurements of III-V Films by Low Temperature Photoluminescence Spectroscopy
Authors: Casson Linda M. , Ndi Francis , Teboul Eric 
Published: January 2010

AbstractPhotoluminescence (PL) spectroscopy is a powerful technique for probing the structures of many types of III-V semiconductor materials. When a semiconductor material is excited at a particular wavelength, electron-hole pairs are generated. The most intense radiative transition is between the conduction band and valence band, and this measurement is used to determine the material band gap. Radiative and non-radiative transitions in semiconductors also involve localized defect levels. The photoluminescence energy associated with these levels can be used to identify specific defects, and the amount of photoluminescence can be used to determine their concentration, and thus predict device quality. At ambient temperatures, the PL signal is typically broad, as much as 100 nm in width. When cooled, structural details may be resolved, and a small spectral shift between 2 samples may represent a change in a structural parameter. Thus a system with high spectral resolution is required.In this paper, a modular Low Temperature Photoluminescence system (LTPL) for measuring optical band gap as a function of temperature is described. Results show that the optical band gap shifts towards higher energy as the sample temperature decreases.
Approaches to Solution Deposited Flexible Composite Vapor Barrier Films
Authors: Gerbec Jeffrey A. , Granstrom Jimmy , Nulwala Hunaid , Campos Luis M. , Hawker Craig 
Published: January 2010

AbstractLiquid resin hybridized silica sol-gels and thiol-ene elastomers were evaluated as compatible materials to form thin film, flexible multilayered structures. Liquid resins are cast and cured in air and ambient pressure on the order of minutes. Scanning Electron Microscopy (SEM) reveals homogeneous interfaces and robust interfacial adhesion under tensile and compressive stress. Thickness of the hybrid glass and thiol-ene films range from 0.80μm to 1.5μm and 8 μm to 16 μm respectively.
Plasma Spray of Nano Composite Ceramics Using Solution Precursors and Combustion Synthesized Nano Powders
Authors: Muoto Chigozie Kenechukwu , Jordan Eric H. , Gell Maurice , Aindow Mark 
Published: January 2010

AbstractPlasma spraying is a well-established method for depositing nanostructured ceramic coatings on structural components. Two different plasma spraying techniques - solution precursor plasma spray (SPPS) and suspension plasma spray (SPS) - have been used to produce MgO-50vol% ZrO2 composite coatings. The microstructural features of the coatings were characterized using Environmental Scanning Electron Microscopy (ESEM) and X-Ray Diffractometry (XRD). The micro hardness of the coatings was measured on cross-sectional samples. The coatings produced using the SPS process with ethanol-based suspensions at a high plasma torch power (45.5 kW) exhibited the densest microstructures with hardnesses as high as ∼1350 HV. However, the backscattered electron (BSE) ESEM characterization of these coatings revealed that the coatings obtained using the SPPS technique had superior chemical homogeneity over those obtained using the SPS technique.
Divacancy-Hydrogen Complexes in Zinc Oxide
Authors: Kuriplach Jan , Brauer Gerhard , Melikhova Oksana , Cizek Jakub , Prochazka Ivan , Anwand Wolfgang 
Published: January 2010

AbstractIn the present work we study Zn+O divacancies filled up with varying amount of hydrogen atoms. Besides the structure and energy-related properties of such defects, we also investigate their capability to trap positrons taking into account positron induced forces. We show that the Zn+O divacancy may trap positrons when up to two hydrogen atoms are located inside the divacancy. The calculated properties are discussed in the context of other computational and experimental studies of ZnO.
P-type Nitrogen Doped ZnO Films Grown By Thermal Evaporation
Authors: Mu Wei , Guo Lei , Kerr Lei , Look David C. 
Published: January 2010

AbstractWe report the formation of p-type nitrogen doped ZnO (ZnO:N) grown by thermal-evaporation deposition. The effects of nitrogen precursors on the electrical and optical properties of ZnO:N were investigated. This study shows that growth process plays a critical role in the electrical properties of ZnO:N. The chemical reaction mechanism was analyzed.
Effect of Aluminum Nitrate Concentration in Zinc Acetate Precursor on ZnO:Al Thin Films Prepared by Spray Pyrolysis
Authors: Jongthammanurak Samerkhae , Phakkeeree Sirirak , Boontongkong Yot , Thanachayanont Chanchana 
Published: January 2010

AbstractAluminium-doped zinc oxide (ZnO) films have been prepared by spray pyrolysis technique using the mixed solution of zinc acetate dihydrate and aluminium nitrate nonahydrate in methanol. Concentration of aluminum in the solution was varied in a range of 1, 3 and 5 atomic percents. The results from X-ray diffraction showed that the preferred orientation of ZnO films changed to the [002] direction when the concentration of aluminum in the solution exceeded 1 atomic percents. ZnO films deposited from the 3 atomic percent Al containing solution had the largest grains and showed the lowest resistivity of 75 Ω-cm. Addition of aluminum into the precursor solution shifted the absorption edge towards longer wavelengths.
High quality p-type ZnO film grown on ZnO substrate by nitrogen and tellurium co-doping
Authors: Park Seunghwan , Minegishi Tsutomu , Park jinsub , Lee Hyunjae , Taishi Toshinori , Yonenaga Ichiro , Oh Dongcheol , Jung Mina , Chang Ji-Ho , Hong Soonku , Yao Takafumi 
Published: January 2010

AbstractNitrogen and tellurium co-doped ZnO (ZnO:[N+Te]) films have been grown on (0001) ZnO substrate by plasma-assisted molecular beam epitaxy. The electron concentration of tellurium doped ZnO (ZnO:Te) gradually increases, compared that of undoped ZnO (u-ZnO). On the other hand, conductivity of ZnO:[N+Te] changes from n-type to p-type characteristic with a hole concentration of 4×1016 cm-3. However, nitrogen doped ZnO film (ZnO:N) still remain as n-type conductivity with a electron concentration of 2.5×1017 cm-3. Secondary ion mass spectroscopy reveals that nitrogen concentration ([N]) of ZnO:[N+Te] film (2×1021 cm-3) is relatively higher than that of ZnO:N film (3×1020 cm-3). 10 K photoluminescence spectra shows that considerable improvement of emission properties of ZnO:[N+Te] with an emergence of narrow acceptor bound exciton (A°X, 3.359 eV) and donor-acceptor pair (DAP, 3.217 eV), compared with those of u-ZnO. Consequently, high quality p-type ZnO with high N concentration is realized by using Te and N co-doping technique due to reduction of Madelung energy.
ZnO Thin Film Transistors for RF Applications
Authors: Bayraktaroglu Burhan , Leedy Kevin , Neidhard Robert 
Published: January 2010

AbstractNanocrystalline ZnO thin films grown by the pulsed laser deposition technique were used to fabricate high performance thin film transistors suitable for RF applications. It was shown that drain current on/off ratios of higher than 1×1012, sub-threshold voltage swing values lower than 100 mV/decade and hysteresis-free operation could be maintained with films grown across a wide temperature range (25°C to 400°C). Films grown at 200°C have the lowest surface roughness and result in devices with the highest current density operation. Devices with 1.2 μm gate lengths and Au-based gate metals had record current gain and power gain cut off frequencies of fT = 2.9 GHz and fmax = 10 GHz, respectively.
Manipulation of Surface Charge on GaN
Authors: Ferguson Josephus D. , Foussekis Michael A. , Ruchala Monika D. , Moore J. C. , Reshchikov Michael A. , Baski Alison A. 
Published: January 2010

AbstractWe have characterized the surface charge on a variety of GaN samples using two surface potential techniques, conventional Kelvin probe and scanning Kelvin probe microscope (SKPM). Kelvin probe was primarily used to measure the change in surface potential under UV illumination, otherwise known as the surface photovoltage (SPV). Due to band bending near the semiconductor surface of about 1 eV in dark conditions, the SPV signal for n-type GaN typically reaches 0.5 to 0.6 eV upon switching on UV light. This value can slowly decrease by up to 0.3 eV during UV illumination in air ambient for 2-3 hours. We report that samples with many hours of ambient UV exposure do not show this slow decrease during SPV measurements, consistent with the UV-induced growth of a thicker surface oxide that limits charge transfer. In addition to prolonged UV exposure, the surface contact potential was also manipulated by local charge injection. In this procedure, the surface is charged using a metallized atomic force microscope tip which is scanned in contact with the sample. Subsequent SKPM measurements indicate an increase or decrease in the surface contact potential for the charged region, depending on the applied voltage polarity. Measurements of the discharge behavior in dark for these regions show a logarithmic time behavior, similar to the decay behavior during our observations of SPV transients after switching off the light. As expected, illumination of the surface increases the discharge rate and restores the charged area to its original state.
Properties of Digital Aluminum Gallium Nitride Alloys Grown via Metal Organic Vapor Phase Epitaxy
Authors: Rodak L. E. , Korakakis D 
Published: January 2010

AbstractDeep Ultra Violet (UV) emitters are of particular interest for applications including, but not limited to, biological detection and sterilization. Within the III-Nitride material system, Aluminum Gallium Nitride (AlxGa1-xN) alloys are the most promising for UV device fabrication due to the wide, direct band gap. The growth of high quality AlxGa1-xN alloys via Metal Organic Vapor Phase Epitaxy (MOVPE) is challenging due to large sticking coefficient of the Al species compared to that of Ga and also the high reactivity of Al precursors. As a result, films are often characterized by large dislocation densities, cracks, and poor conductivity. Digital alloy growth, or Short Period Superlattices (SPS), consisting of layers of binary or ternary alloys with a period thickness of a few monolayers has been shown to be a viable means of growing high quality ternary alloys via Metal Organic Vapor Phase Epitaxy (MOVPE). In certain materials, such as AlGaInP, the electronic properties of digitally grown alloys differ considerably from the equivalent random alloy. Specifically, the bandgap has been shown to differ significantly from the equivalent random alloy. As a result, digital alloy growth presents the potential to further engineer material properties. However, the influence of digital growth on the electronic properties of III-Nitride alloys has not been extensively characterized. This study focuses on Aluminum Gallium Nitride (AlxGa1-xN) alloys grown using a digital technique via MOVPE. The influence of the growth technique over a wide range of compositions is reported along with the electronic properties.