bluuebunny/crossref_metadata_2025 huggingface dataset:
The RET Program in the Center for Materials for Information Technology at the University of Alabama
Authors: Nikles David E. , Warren Garry W.
Published: April 2011

The Center for Materials for Information Technology has a mission of outreach to middle school students. For the past two years our Center has run a summer research experiences for teachers (RET) program. A primary emphasis of the Center's educational outreach activities involves collaboration with a very innovative 6th to 8th grade Integrated Science (IS) curriculum based in the Center for Communication and Educational Technology at the University of Alabama. Each summer three teachers from the IS program spent ten weeks working in the Center to develop demonstrations or activities for use in their classrooms. The emphasis was on demonstrations of magnetism and magnetic materials. In addition to these activities, the teachers have also assisted in the development of Computer Aided Instructional (CAI) software for use in their science classrooms. Both the activities and the software developed this summer will be made available to all of the teachers and students participating in the IS curriculum, approximately 1400 teachers and 170,000 students.
Ways That Engineers Can Get Involved In Recruiting Future Materials Scientists and Engineers
Authors: Gleixner Stacy H.
Published: April 2011

For materials science and engineering departments across the country, recruitment of students is a critical concern. To increase enrollment, students' interest in materials science needs to be sparked early, preferably before they begin college. However, many entering college students have never heard of the major and/or are unsure of what a career in materials science would be like. There are many excellent resources that have been developed to target this problem directly including comprehensive career resources on the web, videos describing careers in materials engineering, and teaching materials developed for middle and high school teachers.
Materials Science and Engineering at Boise State University: Responding to an Industrial Need
Authors: Moll Amy J. , Knowlton William B. , Bunnell David E. , Burkett Susan L.
Published: April 2011

The College of Engineering at Boise State University (BSU) is a new program in only its fifth year of existence. Bachelor's degrees in Civil Engineering (CE), Electrical and Computer Engineering (ECE) and Mechanical Engineering (ME) are offered with M.S. Degrees in each discipline added this year. The industrial advisory board for the College of Engineering at BSU strongly recommended enhancement of the Materials Science and Engineering (MS&E) offerings at BSU. In response to local industry's desire for an increased level of coursework and research in MS&E, BSU has created a minor in MS&E at both the undergraduate and graduate level.

The MS&E program is designed to meet the following objectives: provide for local industry's need for engineers with a MS&E competency, add depth of understanding of MS&E for undergraduate and graduate students in ECE, ME and CE, prepare undergraduate students for graduate school in MS&E, improve the professional skills of the students especially in the areas of materials processing and materials selection, provide applied coursework for Chemistry, Physics, and Geophysics students, and offer coursework in a format that is convenient for students currently working in local industry.
Web Modules Linking Mechanics and Materials Science
Authors: Roylance David , Jenkins C. H. , Khanna S. K.
Published: April 2011

In 1996, the MIT subject 3.11 Mechanics of Materials in the Department of Materials Science and Engineering began using an experimental new textbook approach, written with a strongly increased emphasis on the materials aspects of the subject. It also included several topics such as finite element methods, fracture mechanics, and statistics that are not included in most traditional Mechanics of Materials texts. These nontraditional aspects were designed to fit the curriculum in Materials Science and Engineering, although admittedly Mechanics instructors in other departments and schools might not find all of them suitable for their own subjects. Further, a number of topics may be of interest in educational curricula and industrial practice outside traditional Mechanics subjects.

One approach to increasing the flexibility and adaptability of this materials-oriented text is to make discrete and coherent portions of it available as stand-alone, web-available modules. Instructors could then pick and choose among topics, and assemble a subject offering in whatever way they choose. It would also be possible for instructors of specialty engineering subjects, for instance bridge or aircraft design, to add modules on mechanics of materials aimed at their own needs.

A series of such modules are now being developed under a National Science Foundation Course, Curriculum and Laboratory Improvement (CCLI) grant aimed at strengthening the links in the engineering curriculum between materials and mechanics. Each module is intended to be capable of standing alone, so that it will usually be unnecessary to work through other modules in order to use any particular one. This approach will be outlined and demonstrated, both as an approach to the specific topic of a mechanics-materials linkage, and as a possibility for more general implementation in distance learning.
Dielectric and Electromechanical Behaviour of Relaxor [(1−x)Pb(Mg1/3Nb2/3)O3 -xPbTiO3] Thin Films
Authors: Donnelly N.J. , Catalan G. , Morros C. , Bowman R.M. , Gregg J.M.
Published: April 2011

Thin film capacitor structures of Au / (1−x)Pb(Mg1/3Nb2/3)O3 - xPbTiO3 /(La1/2Sr1/2)CoO3 were fabricated by pulsed laser deposition on single crystal {001} MgO substrates. Films were found to be perovskite dominated and highly {001} oriented. Dielectrically, films displayed relaxorlike features, though maximum permittivity was low compared to single crystal or bulk ceramic (∼1400 at peak @1kHz, for x=0.07, 0.1 & 0.2). A field induced piezoelectric coefficient d33 was measured by piezoresponse atomic force microscopy for specific compositions x =0, × =0.07, and x =0.1 and found to be disappointingly low - indicating poor electric field induced strain. Despite this macroscopic electrostrictive coefficients Q33 were found to be (3.6 ± 0.6) ×10−2C−2m4, (2.6 ± 0.2) ×10−2C−2m4, and (0.9 ± 0.3) ×10−2C−2m4 respectively. Crystallographic electrostrictive coefficients were determined by in-situ x-ray diffraction and found to be (4.9 ± 0.2) ×10−2C−2m4 for PMN-(0.07)PT and (1.9 ± 0.1) ×10−2C−2m4 for PMN-(0.1)PT. Considering that all these Q33 values are of the same order of magnitude as found in single crystal experiments (2.5 – 3.8 ×10−2C−2m4), it is suggested that low out-of-plane strain is entirely a result of reduced polarisability rather than reduced electrostrictive coefficients in thin films relative to bulk ceramic or single crystal. An estimate was also made of the Q13 electrostrictive coefficient for PMN and PMN-(0.07)PT by measuring permittivity as a function of applied in-plane strain. The values obtained were -1.31 ×10−2C−2m4 and -0.46 ×10−2C−2m4 respectively.
Ferroelectric and Displacement Properties of Lead Zirconate Titanate Thick Films Prepared by Chemical Solution Deposition Process
Authors: Iijima Takashi , Hayashi Yoshinori , Onagawa Jun
Published: April 2011

Crack free 10-μm-thick Pb1.1(Zr0.53Ti0.47)O3 (PZT) films were successfully fabricated using a chemical solution deposition process, and the ferroelectric and displacement properties were evaluated. A 0.5 M PZT precursor solution was prepared from trihydrated lead acetate, titanium iso-propoxide, zirconium n-propoxide, and 2-methoxyethanol as the solvent. The process of spin coating and pyrolysis at 500 °C was repeated five times, and then the precursor films were fired at 700 °C for 5 min. This sequence was repeated 30 times. Finally, the films were fired at 700 °C for 10 min. The fabricated crack-free PZT thick films showed (100) preferred orientation. A flat surface and dense microstructure was observed. The electrical properties were comparable with the bulk PZT ceramics. The dielectric constant and dissipation factor were εr = 1453 and tan δ = 0.039, and the remnant polarization and coercive field were Pr = 25 μC/cm2 and Ec = 30 kV/cm, respectively. Field-induced displacement of the films was measured using an atomic force microscope (AFM) with and without a top electrode using a contact mode.
Compositional Effects on the Piezoelectric and Ferroelectric Properties of Chemical Solution Deposited PZT Thin Films
Authors: Kim Dong-Joo , Maria Jon-Paul , Kingon Angus I.
Published: April 2011

The piezoelectric, dielectric, and ferroelectric properties of highly (111)-textured polycrystalline lead zirconate titanate (PZT) films as a function of Zr/Ti composition have been investigated. The peak in piezoelectric coefficient at the morphotropic phase boundary (MPB) observed in bulk PZT ceramics has not been found in thin film PZTs. Measurement of the piezoelectric response as a function of AC amplitude suggests that non-180° domain wall motion in these films is negligible, indicating that the extrinsic contribution to the room temperature dielectric constant is dominated by only 180° domain wall motion. The semi-empirical phenomenological equation relating the piezoelectric coefficient to measured polarization and permittivity values is demonstrated to give an excellent description of the piezoelectric behavior in these films, assuming bulk electrostrictive coefficients. The small deviation between calculated and measured piezoelectric coefficients as well as the dependence of piezoelectric and polarization behavior on the external dc field, i.e., hysteresis loop, are suggested to be primarily due to backswitching of 180° domains.
Hetero-epitaxial Growth of (1, 0, m+1) One Axis-oriented Bismuth Layered Structured Ferroelectrics Thin Films Directly Crystallized by MOCVD
Authors: Nukaga Norimasa , Watanabe Takayuki , Sakai Tomohiro , Suzuki Toshimasa , Nishi Yuji
Published: April 2011

Bismuth layered structured ferroelectrics (BLSF) thin films with different number of octahedron number (m-number) were prepared by MOCVD and directly crystallized on the substrates. Directly-crystallized SrBi2Ta2O9 (SBT) (m=2) films on a (111) Pt/Ti/SiO2/Si substrate were ascertained to have a strong (103) one-axis orientation by the X-ray reciprocal space mapping and to be hetero-epitaxially grown on the (111) Pt grains by the TEM observation. Moreover, directly crystallized Bi2VO5.5 (m=1) and Bi4Ti3O12 (m=3) films deposited on the same substrate showed (102) and (104) one-axis preferred orientations, respectively. These orientations are basically the equal ones with SBT (103) orientation because the tilting angle of c-axis from the substrate surface is also about 55°. Therefore, the direct crystallization is one of the important key techniques for orientation control of BLSF films. Moreover, the directly crystallized SBT film deposited on a (111) Ir/TiOx/SiO2/Si substrate at 570 °C by ECR-MOCVD exhibited (103) one-axis orientation, which also originated from the local epitaxial growth on (111)-oriented Ir grains. The remanent polarization (2Pr), and the coercive field (Ec) of this film were 16.1 μC/cm2 and 83 kV/cm at an applied electric field of 360kV/cm, respectively. This Pr value is about 88% of the expected value of (103)-oriented SBT film from both the Pr values of the (116) and (001)-oriented epitaxial films and detailed crystal analysis.
Iridium Based Electrodes for Ferroelectric Capacitor Fabrication
Authors: Johnson J. A. , Lisoni J. G. , Wouters D. J.
Published: April 2011

Ir and its conductive oxide, IrO2, are candidates to replace Pt as the electrodes in ferroelectric capacitors (FECAPs) because of improved endurance (since e.g. Pt/PZT/Pt shows strong fatigue) and also because of the oxygen barrier properties of Ir/IrO2 stacks that enable the fabrication of stacked FECAPs on top of contact plugs. Two important issues related to these electrodes are the control of the ferroelectric layer orientation on top of these materials, as well as material stability (e.g. oxidation and possible growth of large IrO2 crystallites).

In this work, we show that IrO2 bottom electrodes affect the crystallization of sol-gel deposited Pb(Zr,Ti)O3 (PZT). While PZT films deposited on (111) Pt show a (111) preferential orientation, IrO2 electrodes nucleate strongly different oriented PZT. Controlling and changing the microstructure of the bottom electrode allows tuning of these PZT orientations and the resulting grain morphology, and, consequently, their FECAP polarization hysteresis properties.
Effect of Capacitor Configuration on Oxygen-dependent Electrical Properties of Ferroelectric Pb(Zr,Ti)O3 Thin Films
Authors: McCormick M. A. , Slamovich E. B. , Metcalf P. , McElfresh M.
Published: April 2011

Polarization versus applied field (P-E) hysteresis loop measurements on Pb(Zr,Ti)O3 (PZT) thin films were performed using a controlled-atmosphere probe station. Measurements were made using two different capacitor configurations, each producing differing results. The capacitor configurations included using either the typical arrangement of two top electrodes (planar) or an arrangement using contacts to the top and the bottom electrodes (sandwich). The films included PZT films deposited using pulsed laser deposition (PLD) and commercially-available rfsputtered PZT thin films. Qualitatively similar results were obtained for both types of films. For both PLD and Ramtron PZT films, translation of ferroelectric hysteresis loops along the polarization axis was observed for sandwich capacitors. The magnitude of this voltage was strongly dependent on the partial pressure of oxygen at room temperature. Translations were not observed for the same films using the planar capacitor configuration. However, for both sandwich and planar configurations, the thin film capacitance was sensitive to changes in pO2.
Characteristics of Memory Window and Retention Properties of One Transistor Memory Devices
Authors: Li Tingkai , Hsu Sheng Teng , Ulrich Bruce , Evans Dave
Published: April 2011

Pb3Ge5O11(PGO) metal-ferroelectric-metal-oxide-semiconductor (MFMOS) and metalferroelectric-oxide-semiconductor (MFOS) one-transistor ferroelectric memory devices have been fabricated. The memory windows of the memory transistors can be characterized in terms of MFMOS or MFOS capacitor and the threshold voltages of the transistor. The retention properties of one-transistor memory devices can be measured from the changes of the capacitance of MFMOS or MFOS capacitors. Alternatively the retention properties can be evaluated from the threshold voltages or drain currents of the transistor with retention time. There are inconsistencies between the capacitor data and the transistor data. In this paper, we present the memory windows and retention properties of MFOS and MFMOS one-transistor memory devices measured with various methods. The different results obtained from various methods and device structures will be discussed.
Structural Inhomogeneity of SrBi2Ta2O9Thin Films Prepared by Layer-by-Layer Technique
Authors: Xu J. B. , Hu G. D. , Wong S. P.
Published: April 2011

Grazing incidence x-ray diffraction has been employed to perform the depth-profile analysis on SrBi2Ta2O9 (SBT) thin films with different preferential orientations. For the polycrystalline SBT thin film, the change in structural orientation occurs only within the 15-nm-thick top layer, which is associated with the formation of the (200)-predominant SBT thin film prepared by the layer-by-layer annealing process. The inhomogeneity of structural orientation is more significant in the full film thickness for the (200)- predominant SBT thin film. (0010) peak can only be observed for the grazing angle larger than 0.6°. A layer with the highest ratio of I(200)/I(115) is found in the top surface layer (i.e., the latest layer during deposition) of the (200)-predominant SBT thin film.
Thermal Stability and Electrical Properties of RhO2 Thin Films
Authors: Abe Yoshio , Kato Kiyohiko , Kawamura Midori , Sasaki Katsutaka
Published: April 2011

RhO2 belongs to the family of conducting oxides with a rutile structure, which have attracted attention as capacitor electrode materials for memory devices. In this study, effects of thermal treatment under various oxygen pressures on structural and electrical properties of RhO2 thin films prepared by reactive sputtering were investigated. The RhO2 films were found to be stable up to 700°C under oxygen pressure of 1 atm and a metallic conduction property with a resistivity of about 80 μΩcm was obtained. However, the RhO2 films decomposed to semiconducting Rh2O3 at 750°C. The decomposition temperature decreased to 500°C under oxygen pressures of 0.5-5 mTorr.
Microwave Properties of Strontium Barium Niobate Thin Films Grown by Pulsed Laser Deposition
Authors: Rodríguez-Santiago Víctor , González Yelitza , Fernández Félix E. , Mueller Carl H. , Keuls Fred W. Van , Miranda Félix A.
Published: April 2011

Strontium barium niobate (SrxBa1−xNb2O6 - SBN) with 0.25≤x≤0.75 is a ferroelectric material of interest for diverse optoelectronic applications. Dielectric properties of bulk SBN crystals were comprehensively studied over 30 years ago for a range of compositions and at frequencies up to 30 MHz, but there is little information on properties at higher frequencies. In particular, and up to the best of our knowledge, there are no published results about SBN thin film dielectric properties at high frequencies. For the study reported here, SBN thin films with x = 0.61 were grown on MgO and LaAlO3 substrates by Pulsed Laser Deposition (PLD). Films with good crystallinity and oriented with c-axis normal to the substrate surface were obtained on both types of substrates, while films on MgO had much better texture due to better lattice matching. Interdigital electrode (IDE) capacitors and coupled microstrip phase shifters (CMPS) were fabricated with both types of samples in order to study dielectric response. Capacitance of the IDE capacitors was measured at 1 MHz as a function of temperature and bias voltage, revealing very low losses but poor capacitance tunability, particularly for samples on MgO. Response of the CMPS structures was measured at room temperature and at high frequencies, up to 21 GHz. Insertion losses were measured up to 28 GHz.
Reactive Coevaporation of SrTiO3 Thin Films for Tunable Microwave Devices
Authors: Peng Luke S.-J. , Heinig Nina F. , Moeckly Brian H.
Published: April 2011

We have successfully grown SrTiO3 films on LaAlO3 and MgO substrates up to 2” in diameter using the deposition technique of reactive coevaporation. We have explored a wide range of deposition temperatures, oxygen pocket pressures, and compositions in order to determine the optimal growth process window. X-ray diffraction analyses indicate that the process window for growth on MgO substrates is narrower than for LaAlO3 substrates. Dielectric property measurements show that samples near stoichiometry have higher tunability, but their peak loss tangents are also high (∼0.02). The slightly Sr-poor samples (46-48 at.%) show a reduced loss tangent (<0.01) while maintaining an acceptable tunability (∼50%) at an average electric field of 1.7 V/μm.
Thickness Dependence of Transport Properties of Epitaxial SrRuO3 Thin Films Grown on SrTiO3 Substrates
Authors: Herranz G. , Sánchez F. , García-Cuenca M.V. , Ferrater C. , Varela M. , Martínez B. , Fontcuberta J.
Published: April 2011

To study the effect of the film/substrate interface in thin films we have analyzed the thickness dependence of the transport properties of SrRuO3 films grown on SrTiO3 substrates. Our data makes evident the failure of the so-called deadlayer model to describe the observed thickness dependence of the conductivity. This is interpreted as due to a non-monotonous change of microstructure as thickness increases. Indeed, Atomic Force Microscopy studies indicate substantial modifications of the growth mechanism with thickness.
Photoinduced Heating and Phase Transition in CMR Materials
Authors: Noginova N. , Arthur E. , Ulysse R. , Gillman E. S. , Bonner C. E.
Published: April 2011

Fast switching from conductor to insulator induced by laser light illumination has been studied in single crystals and thin films of La1−xSrxMnO3 in the range of the ferromagnetic phase transition. Based on our experimental data on the photoresponse as a function of temperature, electric current, and intensity, we have demonstrated that the switching and relaxation processes are determined by heating and heat conduction processes. The relaxation time, specific heat and the latent heat constants have been estimated.
Synthesis and Studies of Ti1-xCoxO2 for Device Applications
Authors: Hidalgo A. , Tomar M.S , Melgarejo R.E. , Katiyar R.S.
Published: April 2011

Ti1-xCoxO2 material has reported to show ferromagnetosmat room temperature. Thus, there is research interest in synthesis and structural properties of thismaterial system. The material is synthesized using a soulution chemistry route. X-ray diffraction and Raman spectroscopy is used for the structural characterization.
Stress Evolution During Fe(001) Epitaxy on GaAs(001)
Authors: Koch R. , Nötzel R. , Wassermann B. , Wedler G.
Published: April 2011

Fe films on GaAs substrates have evolved as a model system for the integration of magnetic materials with semiconductors. We report on in situ stress measurements of Fe/GaAs(001), which enlighten the dynamics of the interface formation of this important magnetic metal/semiconductor system. At deposition temperatures of 300 K and 450 K, the stress evolution during growth is very similar. In Fe films thicker than 6–7 nm, the stress is compressive owing to the misfit between the lattices of Fe and GaAs. Thinner films surprisingly are dominated by a tensile stress contribution due to considerable As (and Ga) interdiffusion even at 300 K. Magnetization and in-plane anisotropy of both films are bulk-like.
Critical Magnetism of the CMR Ruddlesden-Popper Manganite La1.2Sr1.8Mn2O7
Authors: Velázquez Matias , Revcolevschi Alexandre , Renard Jean-Pierre , Dupasa Claire
Published: April 2011

We present a thermodynamic study of the critical magnetic properties of La1.2Sr1.8Mn2O7, including the determination of the fundamental characteristics of a magnetic system: anisotropy, critical exponents and crossovers in the vicinity of the Curie temperature, TC∼108K. It appears that two-dimensional correlations above TC do not spread very fast, and that thus the critical fluctuations regime occurs in a moderately narrow temperature range, assessing the three- dimensional nature of the ferromagnetic ordering.
Pulsed Laser Deposition and Characterization of Zn1−xMnxO Films
Authors: Jin C. , Tiwari A. , Kvit A. , Kumar D. , Muth J. , Narayan J.
Published: April 2011

Here we present our results of structural, optical, and magnetic measurements of Zn1−xMnxO thin films. These films were grown epitaxially on (0001) sapphire substrates by using pulsed laser deposition technique. The maximum Mn content (x=0.36) is found to be much higher than allowed by thermal equlibrium limit (x∼0.13) due to the non-equilibrium nature of the pulsed laser deposition. All the films investigated here were found to be single phase with <0001> orientation epitaxial relationship. A linear increase in the c-axis lattice constant was observed with increase in Mn concentration. Optical transmittance measurements showed an increase in the insulating band-gap (Eg) with increase in Mn concentration. DC magnetization measurements showed that there is no long range ferromagnetic ordering down to 10 K.
Effects of As Doping on Properties of ZnO Films
Authors: Huh K. S. , Hwang D. K. , Bang K. H. , Hong M. K. , Lee D. H. , Myoung J. M. , Oh M. S. , Choi W. K.
Published: April 2011

A series of ZnO thin films with various deposition temperatures were prepared on (100) GaAs substrates by radio-frequency magnetron sputtering using ZnO target. The ZnO films were studied by field emission scanning electron microscope(FESEM), x-ray diffraction(XRD), photoluminescence(PL), cathodoluminescence(CL), and Hall measurements. The structural, optical, and electrical properties of the films were discussed as a function of the deposition temperature. With increasing temperature, the compressive stress in the films was released and their crystalline and optical properties were improved. From the depth profile of As measured by secondary ion mass spectrometry(SIMS), As doping was confirmed, and, in order to activate As dopant atoms, post-annealing treatment was performed. After annealing treatment, electrical and optical properties of the films were changed.
Growth of the Single-Crystalline ZnO Films on Si (111) Substrates by Plasma-Assisted Molecular-Beam Epitaxy
Authors: Koike Kazuto , Tanite Takanori , Sasa Shigehiko , Inoue Masataka , Yano Mitsuaki
Published: April 2011

This report describes the growth of single-crystalline ZnO films on Si (111) substrates by plasma-assisted molecular-beam epitaxy. X-ray diffraction measurement shows that c-axis oriented ZnO films are easily grown on Si (111) substrates. However, in-plane random rotational domains are included in the ZnO films due to the inevitable oxidation of substrate surface at the initial stage of ZnO growth. By employing a thin CaF2 buffer layer between the ZnO films and Si substrates, we have succeeded in suppressing the generation of rotational domains and in obtaining an intense ultraviolet photoluminescence even at room temperature. These results indicate that the use of CaF2 buffer layer is promising for the growth of device-quality ZnO films on Si (111) substrates.
Nature and Formation of Non-Radiative Defects in GaNAs And InGaAsN
Authors: Chen W. M. , Thinh N. Q. , Buyanova I. A. , Hai P. N. , Xin H. P. , Tu C. W. , Li Wei , Pessa M.
Published: April 2011

The optically detected magnetic resonance (ODMR) technique has been employed to examine the nature and formation mechanism of non-radiative defects in GaNAs and InGaAsN. In both alloys, two defects were observed and were shown to be deep-level, non-radiative recombination centers. One of the defects has been identified as a complex involving an AsGa antisite. These two defects gain more importance with increasing N composition up to 3%, presumably due to an increase in their concentration. With a further higher N composition, the defects start to lose importance in carrier recombination that is attributed to an increasingly important role of other new non-radiative channels introduced with a high N composition. On the other hand, effect of In composition up to 3% seems to be only marginal. Both defects were shown to be preferably introduced in the alloys during low-temperature growth by molecular beam epitaxy (MBE), but can be rather efficiently removed by post-growth rapid thermal annealing.
Multi-Color Quantum Well Infrared Photodetectors for Mid-, Long-, and Very Long- Wavelength Infrared Applications (invited)
Authors: Li Sheng S.
Published: April 2011

Quantum well infrared photodetectors (QWIPs) have been widely investigated for the 3–5 μm mid-wavelength infrared (MWIR) and 8–12 μm long-wavelength infrared (LWIR) atmospheric spectral windows as well as very long wavelength infrared (VLWIR: λc 14 μm) detection in the past decade. The mature III-V compound semiconductor growth technology and the design flexibility of device structures have led to the rapid development of various QWIP structures for infrared focal plane arrays (FPAs) applications. In addition to the single-color QWIP with narrow bandwidth, the multi-color QWIP required for advanced IR sensing and imaging applications have also been emerged in recent years. Using band gap engineering approach, the multi-color (2, 3, and 4- color) QWIPs using multi-stack quantum wells with different well width and depth and voltage-tunable triple- coupled quantum well (TCQW) structure for detection in the MWIR, LWIR, and VLWIR bands have been demonstrated. In this paper, the design, fabrication, and characterization of a voltage-tunable 2-stack 3-color QWIP for MW/LW/LW IR detection and a 3-stack 3-color QWIP for detection in the water, ozone, and CO2 atmospheric blocking bands are depicted.
Photoluminescence From Er− Implanted 4h And 6h-SiC
Authors: Uekusa Shin-ichiro , Goto Takayuki
Published: April 2011

Erbium (Er) ions were implanted into 4H and 6H silicon carbide (SiC). The temperature-dependent photoluminescence (PL) and PL lifetime were characterized. The optimum annealing temperature for SiC : Er were 1600 °C, PL intensity decreased at 1700 ° C, and the bandedge luminescence changed in relation to the luminescence of Er3+. Thermal quenching of the luminescence of Er3+ was suppressed by using SiC with a wide band gap as a host material. The Er3+ -PL was observed at room temperature (RT). We monitored the auger effect that is believed to be the main cause of the thermal quenching process and concluded that, in the temperature range 15 K to 70 K, the thermal quenching process has a close relation to nonradiative recombination from the first excited state (4I13/2) to the ground state (4I15/2) of Er3+.
Control of ZnO Morhpology by Solution Route
Authors: Sun Lingdong , Zhang Jun , Liao Chunsheng
Published: April 2011

In this paper, ZnO with a rich variety of well-defined morphologies have been achieved by solution route using different kind of precursors, which can prepare particles by only one step without calcination. The influences of solvent, and temperature on the particle size and morphology of ZnO were investigated. It was revealed by the scanning electron microscope (SEM) and transmission electron microscope (TEM) images that the morphological feature of ZnO can be controlled as rod-, polyhedron-, fluffy sphere-, snowflake- and flower-like, etc. XRD measurement showed that all of the ZnO samples with different morphologies has the same hexagonal structure, which is well consistent with electron diffraction (ED) characterization. This communication not only provides promising candidates for materials science due to the importance of shape in relationship with materials, but also presents an effective route to synthesize the well-defined inorganic materials.
Optically Detected Magnetic Resonance Study of Core-Shell and Alloy Nanocrystals of HgTe and CdS
Authors: Fradkin L. , Langof L. , Lifshitz E.
Published: April 2011

The synthesis of HgTe nanocrystals (NCs), coated with a CdS shell, presumably results in the formation of HgTe/CdS, HgTe/CdHgS core-shell structures or separated CdHgS alloys. Photoluminescence (PL), continuous-wave (cw) and time-resolved optically detected magnetic resonance (ODMR) spectroscopy examined the magneto-optical properties of the dominating resonance aforementioned products. The cw ODMR measurements indicated that the NCs exhibit a band, centered at 0.39 Tesla, corresponding to an excited state electron (e) and hole (h) spin manifold, with total angular momentum (F=S+L) Fe=1/2 and Fh=3/2, respectively. Theoretical simulation of the ODMR band revealed an anisotropy of the g-factor, indicating the existence of trapped carriers' at a mixed Cd-Hg tetrahedral site, confirming the formation of an alloy component. The time-resolved ODMR measurements reveal a characteristic radiative decay time and spin-lattice relaxation time of these trapped carriers of hundreds of microseconds.
Current Images of CdSe Colloidal Nanodots Observed by Conductive-tip Atomic Force Microscopy
Authors: Tanaka Ichiro , Kawasaki Eri , Ohtsuki O. , Hara M. , Asami H. , Kamiya I.
Published: April 2011

We have fabricated submonolayer-thick films of CdSe colloidal nanodots in order to investigate electronic properties of individual nanodots by conductive-tip atomic force microscopy (AFM). Topographic and current images of isolated single CdSe colloidal dots on single crystalline Au (111) surface which was covered with dodecanethiol self-assembled monolayer were obtained by AFM operating in contact mode with a conductive tip under appropriate bias voltages. In the current image, it is found that the dot regions have higher electric resistances due to tunneling resistance through the CdSe dots. We also found 10 nm-scale electric inhomogeneity around the dots, which may corresponds to the previously reported etch-pits of Au (111) surfaces formed during the deposition of the dodecanethiol molecules.
Continuous and Time Resolved Optically Detected Magnetic Resonance Studies of InP Nanoparticles
Authors: Langof L. , Ehrenfreund E. , Lifshitz E. , Micic O. I. , Nozik A. J.
Published: April 2011

Carriers in small colloidal InP nanoparticles are in strong quantum confinement regime. The low temperature photoluminescence spectrum of InP nanoparticles is composed of an excitonic luminescence at high energies and a non-excitonic defect emission band at lower energies. HF etching of the nanoparticles reduces the defect emission and enhances the exciton process.

In this work we apply optically detected magnetic resonance spectroscopy (ODMR) both in continuous wave and time resolved mode (TR-ODMR) to study the defect luminescence in InP nanoparticles. The results show that the defect luminescence originates from weakly coupled electron-hole pair, where the electron is trapped at the surface by phosphorous vacancy, Vp, and the hole is located at the valence band. Additionally, the results suggest that the non-etched samples are dominated by Vp at the surface. Those are mainly eliminated upon HF treatment, leaving behind small percent of Vp in the core of the nanoparticle. We also find the electron-hole exchange interaction from circular polarized ODMR measurements. The TR-ODMR measurement further clarifies the spin dynamics and characteristic of the magnetic sites. Fitting these measurements to the simulated response of the PL intensity to the square wave modulated microwave power revealed that the spin relaxation time and radiative lifetime of electron-hole pair in the nanoparticles are in the microseconds regime.
On the Optical Memory of a Thin-Film pInSb-nCdTe Heterojunction Obtained by Laser Pulsed Deposition
Authors: Alexanian Arik G. , Aramyan Nikolay S. , Grigoryan Romen P. , Khachatrian Ashot M. , Matevossian Lenrik A. , Yeremyan Arsham S.
Published: April 2011

Thin film pInSb-nCdTe heterojunctions (HJs) were produced using pulsed laser deposition (PLD) technique and their photoelectric properties were studied for various thickness of the CdTe layer at nitrogen temperature and under a background radiation the photo-EMF for which was around 1.5 mV. At radiative excitation of the HJ a photo-EMF is observed, which persists when the excitation is turned off. The optical memory (OM) effect is observed in an idling regime and in a wide spectral range: (0.37–1.37)μm with “recording” (0.37–0.575)μm, (0.75–1.37)μm, and “clearing” (0.575–0.75)μm sub-regions. The maximum OM signal is observed at λ=0.575μm while the minimum is at λ=0.768μm. In the spectral dependence of the OM signal at direct and reverse scanning of monochromatic irradiation an hysteresis is observed which is evident for the OM effect. The time dependence of OM signal is investigated at λ=0.575μm and at various intensities of the radiation source. Here, an effect of saturation is clearly observed, and the time during which the OM signal runs up to saturation, depends strongly on the incident light flow power and decreases drastically as the latter is increased. The external bias applied to the HJ enhances the OM on 2 orders over its value in the idling regime. The OM signal persists for a time period no less than 105 sec, either with or without an external bias. The actually obtained values of “recording” sensitivity and the “recording” time are U=0.66 μJ/mm2 and τ=10−4 sec., respectively. The OM signal reaches its maximal value as the thickness of CdTe layer increases (up to d=0.45 μm). It is shown that the investigated HJ possess the property of integration of the radiation.
Doping profiles of n-type GaAs layers grown on Si by the conformal method
Authors: Ardila Angel M. , Martínez O. , Avella M. , Jiménez J. , Gérard B. , Napierala J. , Gil-Lafon E.
Published: April 2011

We study doping profiles in selectively Si-doped GaAs layers grown by the conformal method. This growth technique allows to obtain GaAs/Si with optoelectronic quality. The samples are laterally grown, and selective doping with Si is carried out in such a way that doped stripes are intercalated with undoped ones. The study of the doping profiles was carried out by cathodoluminescence (CL) and micro-Raman (μR) spectroscopy. Abrupt doping profiles between doped and undoped stripes were demonstrated by monochromatic CL images. Deep level related CL bands can be observed between 1000 and 1400 nm, evidencing the complex mechanism for Si incorporation at the growth temperature (730 °C). Net doping concentrations and mobilities across the layers were determined from the analysis of the phonon-plasmon coupled modes in the μR spectra obtained with a lateral resolution better than 1 μm.
Gallium vacancy in GaSb studied by positron lifetime spectroscopy and photoluminescence
Authors: Mui W. K. , Lui M. K. , Ling C. C. , Beling C. D. , Fung S. , Cheah K. W. , Li K. F. , Zhao Y. W.
Published: April 2011

Positron lifetime technique and photoluminescence (PL) were employed to study the vacancy type defects in p-type Zn-doped and undoped GaSb samples. In the positron lifetime study, Ga vacancy related defect was identified in these materials and it was found to anneal out at temperature of about 350°C. For the PL measurement on the as-grown undoped sample performed at 10K, a transition peak having a photon energy of about 777meV was observed. This transition peak was observed to disappear after a 400°C annealing. Our results is consistent with the general belief that the 777meV transition is related to the VGaGaSb defect, which is the proposed residual acceptor of GaSb.
Defects Created by 25 keV Hydrogen Implantation in n-type GaN
Authors: Auret F. D. , Meyer W. E. , Laarhoven H. A. van , Goodman S. A. , Legodi M. J. , Beaumont B. , Gibart P.
Published: April 2011

We have studied defects introduced in n-GaN during 25 keV hydrogen and 40 keV He implantation using deep level transient spectroscopy (DLTS). These measurements revealed that 25 keV hydrogen implantation introduces a complex set of electron traps, of which most are different to the defects observed after high-energy (MeV) electron and proton implantation. At least three of the defects detected after 25 keV proton implantation exhibit a metastable character in that they can be reproducibly removed and re-introduced during reverse and zero bias anneal cycles. Isochronal and isothermal annealing experiments yielded low activation energies of approximately 0.1 – 0.2 eV for both processes. By comparison, 40 keV He ion implantation introduced the same metastable defects, but in different relative concentrations.
Study of Interface Properties of InN and InN-Based Heterostructures by Molecular Beam Epitaxy
Authors: Lu Hai , Schaff William J. , Eastman Lester F. , Wood Colin
Published: April 2011

In this work, we prepared epitaxial InN on (0001) sapphire with an AlN or GaN buffer layer by molecular beam epitaxy (MBE). A series of samples were grown with different thickness under the optimized growth conditions. Films were characterized by x-ray diffraction (XRD), reflective high-energy electron diffraction (RHEED), atomic-force microscopy (AFM), transmission electron microscopy (TEM) and Hall measurements. By extrapolating the fitted curve of sheet carrier density vs. film thickness to zero film thickness, a strong residual sheet charge was derived, which may be located at the interface between the buffer layer and the InN film, or at the near-surface. It was found that for InN film on AlN buffer, the residual sheet charge is about 4.3×1013 cm-2, while for InN films on GaN buffer, the residual sheet charge is about 2.5×1013 cm-2. At present, we tentatively believe that the residual charge is surface charge accumulation similar to what is observed at the InAs surface. InN samples with Hall mobility beyond 1300 cm2/Vs and carrier concentration below 2×1018 cm-3 were routinely achieved in this study.

The first study on InN-based FET structures was performed. Amorphous AlN was used as the barrier material, which was prepared by migration enhanced epitaxy (MEE) at low growth temperature. It was found that the surface morphology is improved after an AlN barrier layer is added to InN. Hg was used as a back-to-back Schottky metallization. Very low leakage current and weak rectifying behavior were observed.
Reverse-annealing phenomenon during the high-temperature implantation of Ar+ into GaN
Authors: Usov Igor O. , Parikh Nalin R. , Thomson Darren , Davis Robert F.
Published: April 2011

A systematic investigation of the damage accumulation in GaN films induced by 150keV Ar ions as a function of implantation temperature and dose rate has been conducted. The depth distribution of the disorder in the Ga sublattice has been measured by RBS/channeling spectrometry with a glancing angle detector geometry to provide enhanced depth resolution. Two disordered regions were identified in the damage depth distribution: a near-surface peak and a bulk damage peak. These regions exhibit different behavior as a function of implantation temperature. The height of the near-surface peak, as expected, decreased with implantation temperature approaching the magnitude of the unimplanted sample. The displaced atomic density in the bulk damage peak also followed this tendency and decreased in the temperature range from room temperature to 500°C. The implantation at higher temperatures resulted in an increase in the amount of damage, reaching a maximum at about 700°C and displayed a characteristic “reverse annealing” behavior. Further increase of the implantation temperature to 1000oC reduced the disorder. The influence of the dose rate and implantation temperature on the radiation damage accumulation is discussed.
Production Scale Growth of AlGaN/GaN Field Effect Transistors
Authors: Gotthold David , Gibb Shawn , Peres Boris , Ferguson Ian , Palmer Chris , Armour Eric
Published: April 2011

This paper addresses issues with the manufacturability of AlGaN/GaN FET structures. A robust Metalorganic Chemical Vapor Deposition growth process has been developed that will now allow reliability measurements to be obtained on the resulting devices. During a small scale production run mobilities in excess of 1600 cm2/V.s, sheet charge (Ns) between 0.8x1013 and 1.2x1013 cm-2, and Rs<400 Ω/square with less than 2% variation across the wafer and less than 0.5% variation from wafer to wafer were obtained. Issues for producing a manufacturable process on sapphire and semi-insulating SiC substrates using in-situ monitoring will be addressed. The equivalence of growth on sapphire and SiC substrates for process optimization will be shown.
Electric Field Induced Heating and Energy Relaxation in GaN
Authors: Eckhause T. A. , Süzer Ö. , Kurdak Ç. , Yun F. , Morkoç H.
Published: April 2011

We report results of an investigation of electric field induced heating at low temperature in GaN 3-dimensional electron gas films grown on sapphire substrates. The excess noise of the electron gas in a patterned GaN film, while the substrate is held at low temperature, is used to determine the electron temperature. We calculate the rate of power dissipation and compare our results with a calculation of acoustic deformation potential scattering processes in GaN. We discuss the existence of a thermal boundary resistance between the GaN film and the sapphire substrate.
Chemical, Electrical, and Structural Properties of Au/Pd Contacts on Chemical Vapor Cleaned p-type GaN Surfaces
Authors: Hartlieb P. J. , Roskowski A. , Rodriguez B. J. , Nemanich R. J. , Davis R. F.
Published: April 2011

The chemical, electrical, and microstructural properties of Au/Pd contacts on p-type GaN(0001) surfaces previously cleaned either ex situ or ex situ and in situ have been investigated. The in situ process involved a high temperature, NH3-based chemical vapor clean (CVC); it produced ordered, stoichiometric, p-type GaN surfaces with no detectable C and an O constituent which was subsequently reduced from 15 at% on the ex situ treated surface to 2 ± 1 at% following the CVC process. The Pd contacting layer grew epitaxially in a layer-by-layer mode on the CVC surface and formed an abrupt, unreacted metal-semiconductor interface. The Au capping layer also grew epitaxially on the Pd. Au/Pd contacts on both HCl and CVC treated surfaces exhibited identical surface roughness values (RMS) in the as-deposited state and following a 500°C anneal. Contact structures on CVC treated surfaces demonstrated excellent high-temperature microstructural stability as evidenced by the absence of significant change in the surface roughness (RMS) with successive annealing at 600 and 700°C. Identical contact structures on ex situ cleaned surfaces exhibited poor high temperature microstructural stability, as indicated by a significant increase in the surface roughness (RMS) following successive anneals at 600 and 700°C. There was a significant degradation in the morphology of both surfaces following the 800°C anneal as evidenced by the formation of large voids in the contact metallization and the exposure of the underlying p-type GaN substrate. The lowest resistance contact structures with uniform metal coverage were obtained for Au/Pd contacts on a CVC treated surface annealed at 700°C.
Layer by Layer Growth of GaN Films by Low Temperature Cyclic Process
Authors: Sanguino P. , Koynov S. , Niehusl M. , Melo L. V. , Schwarz R. , Alves H. , Meyer B. K.
Published: April 2011

Recently we have proposed a new layer-by-layer method for deposition of group-III nitrides from elemental precursors (Ga, N2). This technique is based on a two-step cyclic process, which alternates Pulsed Laser Deposition (PLD) and nitrogen plasma treatment. We have shown that such a process allows to control independently the structure and the N-content of the growing film. The objective of this work is to develop the cyclic process for achieving high quality GaN films. We explore the opportunities to grow stoichiometric epitaxial films on different substrates at relatively low temperatures (400°C to 600°C). This will gives us the possibility to use ZnO epitaxial layers as a buffer without thermal degradation. UV- Visible transmission spectra, X-ray diffraction scans and Atomic Force Microscopy are some of the tools used to characterise and compare the deposited films.
Structural and Optical Characteristics of Laterally Overgrown GaN Pyramids on (111) Si Substrate
Authors: Cho Yong-Hoon , Kim H. M. , Kang T. W. , Song J. J. , Yang W.
Published: April 2011

Structural and optical characteristics of laterally overgrown GaN pyramids on a (111) Si substrate were investigated by scanning electron microscopy, transmission electron microscopy (TEM), and cathodoluminescence (CL) microscopy and spectroscopy. Cross-sectional TEM images revealed that the threading dislocation density over the window openings is very high, but gradually decreases with increasing GaN thickness, and that dislocations observed over the mask are parallel to the mask interface. Cross-sectional-view CL images taken at different emission wavelengths clearly showed significant differences between the overgrown areas on top of the mask and the coherently grown regions over the windows. A clear reverse contrast in the cross-sectional CL images of bandedge (identical contrast in case of yellow-band) emission was observed by comparing the defect density observed in cross-sectional TEM images. The CL peak intensity ratio of band-edge-emission to yellow luminescence was also investigated as a function of position in the GaN pyramid cross section. It was demonstrated that there exists a strong correlation between structural defects and optical properties in laterally overgrown GaN pyramids on (111) Si substrate.