I want to acknowledge my advisors Harry Atwater and Nate Lewis for letting me join their groups and work freely on the diﬀerent projects I’ve encountered. In addition, Bruce Brunshwig and Kimberly Papadantonakis have been most valuable in getting the important things done. I appreciate the funding and instrumentation from the Molecular Materials Research Center in addition to instrumentation in the Joint Center for Artificial Photosynthesis. Funding and support from the Dow Chemical Company has made most of my work possible. I thank Robert Wright and Rebekah Feist for leading the Caltech-Dow Earth-Abundant Semiconductor partnership for the numerous years and graduate projects it has helped complete. I thank Alireza Ghaﬀari for technical instrument assistance, and Mike Roy, Steve Olsen, Carol Garland, Rick Gerhart, and Jeﬀ Groseth for their professional work and analysis. I thank Barbara Miralles, Tiﬀany Kimoto, Jennifer Blankenship, Christy Jenstad, Liz Jennings, and Lyann Lau for their administrative assistance in planning great parties and important events.
Electron Beam Induced Current (EBIC) is an electron microscopy-based technique that can provide information on the electrical properties of semiconductormaterials and devices. Since the size of electronic devices has reached the nanometer scale, the Scanning Electron Microscopy (SEM)-based EBIC technique has reached its spatial resolution limits. Therefore, there is a need for a high-resolution EBIC technique. This chapter focuses on the design, development and implementation of an EBIC system utilizing a dedicated Hitachi HD-2000 Scanning Transmission Electron Microscope (STEM) [6.1]. The combination of a high energy electron beam and a thin sample in a STEM improves the spatial resolution to the nanometer scale, as discussed in Chapter 3 and shown in Figure 3.2. The STEM-EBIC technique was used in the characterization of an indium gallium nitride (InGaN)-based quantum well Light Emitting Diode (LED). A novel sample preparation method using a Focused Ion Beam (FIB) technique and a custom STEM-EBIC sample holder were designed for these experiments. The relative position of the p-n junction with respect to a thin In x Ga 1-x N quantum well (QW) was
The improving performance of short fiber lasers is di- rectly linked to the development of large core single-mode fibers. The most successful and flexible approach to in- crease the core size while maintaining single-mode proper- ties present recently developed micro-structured fibers where two-dimensional periodic refractive index structures surround the fiber core . Applying a special micro- structured fiber design 3 in combination with highly doped phosphate glass 4.7-W output has been demonstrated from a fiber laser with only 3.5-cm of active single-mode fiber corresponding to a yield above 1.3-W per cm (see Fig. 1). An slope efficiency of ~20% with respect to the launched pump. The output spectrum is centered at 1535 nm with a linewidth of ~2 nm.
The 1950s was a decade of Transistor. It marked the end of the development of sophisticated vacuum tube system and the beginning of the semiconductor age. The age of semiconductor electronics began with the invention of the transistor in 1948. However this ERA originated in earlier work performed between 1920 and 1945. Semiconductor opened the floodgate to further development in electronics. The first integrated circuit (ICs) appeared in the market during the early sixties. Man desire to conquer space accelerated this growth even further the semiconductor age had truly began. Now during the eighties this tremendous growth rate is not only continuing but is accelerating every year. The use of values nearly became obsolete during the sixties. Due to the rapid developments in integrated circuit technology starting from the small scale integration then medium scale integration large scale integration (VLSI) technique even the use of individual transistor in becoming unnecessary the vast changes that have taken place during the last so years can best be understood by noting the reduction in size and price of modern digital computers.
At present time the more and more increasing demands of the technology and communications market push the manufacturers of optoelectronic devices towards further reduction of the dimensions of the active device in the integrated circuits to obtain greater functionality and performance at lower cost. Traditional Si-based semiconductor technology has almost exhausted its own resources and future development is impossible without the introduction of other materials, such as GaAs (which is widely used for production of light- emitting diodes, solar cells, and high-power transistors), Ge (which forms Si/SiGe heterostructures and thus opens the way for carrier mobility enhancement and band structure engineering) and urgently required high- κ dielectrics for substitution of SiO 2 as an insulator.
We have described mobile phone systems trends, requir ements, and work on high-frequency semiconductordevelopment ongoing at Hitachi. High- frequency semiconductors greatly influence the realization of mobile phones featuring smaller size, lighter weight, and longer talk-time, and strong demand exists for devices with higher efficiency, higher performance, and higher integration. We expect to continue our progress in developing high-frequency semiconductors suitable for many types of communications systems.
deposited. 5 nm of aluminum was finally evaporated. An attempt was also made using the sputter system without breaking the vacuum. However, during the development of the exposed resist, the Al layer was developed away, which could indicate a porous film. This may be because of the low power used to sputter Al. Without sufficient energy to coalesce, the atoms might just have simply hit the wafer and adsorbed, leading to a low quality film. Evaporated Al, on the other hand, has more thermal energy and the atoms can form a dense film. After the first lithography, 15 nm of TiN was sputtered on samples G and H and then lifted-off. Different methods and temperatures of annealing were tried on each sample: 1 h at 600 ◦ C in a nitrogen furnace, 20 sec at 850 ◦ C in RTA and 1 sec at 1000 ◦ C in RTA. The rest of the process is similar to sample D and the final devices schematic can be seen in Figure 6.6 .
and proteoglycan matrix present during development, with features on the micro- and nanoscale. As the spatial resolution of surface patterning techniques improves, experiments are able to present substrate topographies that more closely emulate the physical environment of this collagen-protein meshwork. The range of materials used for topographic studies has also expanded to include metal and semiconductor substrates, with some emphasis given to interfacing microelectronic devices with cells. 55 A summary of some substrate materials, topographies, and subsequent effect on cell growth is provided in Table 2.3 and 2.4 for semiconductor or metal substrates and polymer sub- strates, respectively. Recurring cell types include neurogenic lines (e.g. PC12 cells, cerebellar granule neurons) and fibroblasts (e.g. NIH 3T3, L929.) Neurotypic cells extend long axonal projections, and the growth cone that directs filopodial extension is highly sensitive to local mechanical and chemi- cal stimuli, 56 making the response of these cells to external or surface-bound stimuli particularly prominent. Fibroblasts are also emphasized due to their extremely well established characteristics, morphological response to substrate properties, and their role in collagen production. 9 As discussed in Section 2.2, collagen is a significant element of the ECM, and any change to collagen production from influencing fibroblasts is likely to propagate through the ECM to other cells in a complete living tissue. While this represents a small sample of existing studies, it is intended to illustrate the variability in both cell lineage selected as well as parameters of interest. There is general agreement that cell viability, density, and morphology are important, but quantification of these parameters - particularly morphology - is highly inconsistent. Additionally, there remains no consistent iden- tification and quantification of parameters specific to a given cell type, such as mineralization of osteoblasts or number and length of neuritic extensions in neurotypic cells.
In 1990, he joined Analogy (now owned by Synopsys), where he focused on semiconductor de- vice modeling and the research and development of hardware-description-language-based modeling tools and techniques, and was named a Distinguished Member of the Technical Staff in 1996. He is also engaged in analog and mixed- signal IC design and power electronics. In 1998, he joined the Department of Electrical Engineering, University of Arkansas, as an Associate Professor, where he was promoted to a Full Professor in 2002, and helped establish the National Center for Reliable Electric Power Transmission in 2005, for which he serves as the Director. In 2003, he cofounded Lynguent, an electronic design automation company focused on modeling and simulation tools. He has authored or coau- thored more than 100 refereed articles on modeling and IC design. He holds patents on software architecture and algorithms for modeling tools and has oth- ers pending. He is a coauthor of the book Modeling With an Analog Hardware Description Language (Kluwer). He was a Guest Editor of the Institution of Engineering and Technology Computers and Digital Techniques.
The development of technology based on GMR, a phenomenon first reported in 1988 , has been the most commercially viable application to date. GMR occurs in a multi-layered structures composed of a non-ferromagnetic layer sandwiched between two ferromagnetic layers. The ferromagnetic layers naturally align themselves in an anti-parallel state. As electrons with mixed spin states pass through the structure they experience a large amount of scattering. In the presence of a magnetic field, the ferromagnetic layers are aligned in a parallel state and the population of electrons with parallel spins pass through with less scattering, leading to a decrease in the electrical resistance of the structure. The near ubiquitous application of GMR to hard drive sensing technology led to a dramatic increase of drive storage size and had an undeniable effect on the current state of computing .
The presence of an ordered array of semiconducting quantum dots within the junction of a p-type / intrinsic / n-type cell may lead to the formation of an energy band or bands within the bandgap of the solar cell. These aforementioned quantum dot mini- bands could potentially serve as intermediate bands thereby enabling the physical development of intermediate band solar cells. The presence of these mini-band states allows for harvesting of lower energy (longer wavelength) photons that would normally be un-absorbed by the cell. The key to this device is that the low energy photons can be harvested without also having the unwanted effects of voltage and efficiency degradation, which is associated with using an ordinary narrow bandgap device for converting such photons. Devices comprised of InAs quantum dots within a GaAs host are currently under investigation for use as the middle junction in multijunction space solar cells [48- 50]. In this device, the role of the quantum dots is also to extend the band edge of the middle junction device to longer wavelengths, thereby increasing the current of the middle junction and the entire current matched stack. In such a device, however, a small reduction in voltage could be tolerated. These quantum-dot “enhanced” multijunction solar cells have a theoretical one-sun limiting efficiencies of over 45% .
Good electronic properties are essential to the efficacy of semiconductordevices. Optoelectronic devices rely not only on strong interaction with light, but also on the capacity to transport charge efficiently. For devices implementing p-n junctions, the ability to dope a semiconductor is also very valuable. III-nitridematerials have come to be recognized as favorable materials for such applications, mostly because they have tunable bandgaps with direct transitions. The polar wurtzite crystal structure of III-nitrides also allows for certain attributes that could be advantageous in devices such as piezoelectricity and non-linear optical properties, which are not observed in other common semiconductors like silicon and GaAs. The zinc-IV-nitridematerials are predicted to have crystal and electronic structures similar to those of the III-nitrides, so the same device advantages could be expected for these new earth-abundant compound semiconductors.
RF-plasma MBE has also been very successfully used for the development of high mobility 2-D electron gases (2DEGs) in the AlGaN/GaN system. For growth on Ga polar templates, a fixed positive sheet charge exists at the AlGaN/GaN interface due to the discontinuity in the total polarization between AlGaN and GaN. When the AlGaN cap layer exceeds a minimum thickness, a 2DEG forms at the interface. Contrary to results in MOVPE AlGaN/GaN structures, the 2DEG mobility for MBE AlGaN/GaN struc- tures decreases with increasing sheet carrier concentration . This indicates that the dominant scattering mechanism in MBE structures is either alloy scattering or interface roughness and not ionized impurity scattering. Thus, the highest mobilities in MBE structures have been realized at low Al concentrations and now exceed 60 000 cm /V s at 4 K , a value about twice as large as reported in the best MOVPE AlGaN/GaN structures. This overall improvement in mobility is likely due to the reduction in unintentional impurity incorporation in the MBE environment. Similar to the results for n-GaN and p-GaN, 2DEGs with superior elec- trical properties are realized when the growth is conducted at the cross over from the intermediate Ga-rich regime to the Ga-droplet regime .
A comparison between the three models of the semiconductor bandstructure described is shown graphically in figure 1.3. The Pidgeon and Brown 8-band k · p model gives three valence bands (heavy, light and spin-orbit split-off hole bands) and one conduction band. A single conduction band and valence band (light hole) are shown for the α-approximation, and finally, the parabolic approximation is shown for the conduction band only. For each case, the parameters for InSb were taken from a review of III–V semiconductors . For the narrow gap semiconductor InSb, it is expected that the 8-band Pidgeon and Brown model will give the most accurate description of the bandstructure, as it takes into consideration the effect of higher bands, in addition to the 8-bands explicitly considered. In addition, unlike the 2-band model, it makes no assumption with respect to the spin- orbit split-off energy, ∆ so . With increasing k, the parabolic expression will give the most
As a first step materials can be divided into insulators, semiconductors and metals, de- pending on the free carrier concentration of the material. All three parameters defining the figure of merit depend on this free carrier concentration, Figure 3 shows this de- pendence for the Seebeck coefficient, electrical conductivity and thermal conductivity as well for the figure of merit. From this figure one can see that the figure of merit reaches a maximum in the region of heavily doped semiconductors. Consequently, this will be the type of material of interest to adapt in order to further increase the figure of merit. In this report we model an isotropic material consisting of multiple crystallites. The area where crystallites meet are known as grain boundaries.
T ransition m etal nitrides provide im portant refractory m aterials, such as "superhard" cerm ets for m echanically-resistant coatings, force-transm itting elem ents, and as useful m agnetic and conductive m aterials, including high-Tc superconductors [3, 7]. T hroughout the years, the scientific com m unity has m easured m any o f the relevant m aterial properties o f transition m etal nitride com pounds and com posites, such as the hardness, shear m oduli, superconducting transition tem perature. H ow ever, there is little inform ation on the bulk m odulus o f the pure m aterials, w hich gives direct inform ation on the volum e com pressibilities o f the nitride com pounds, that one can correlate w ith their electronic properties, and especially the cohesive energy [3, 7]. In this, chapter we present com pressibility m easurem ents for five transition m etal nitrides that constitute im portant m aterials (5-M oN, y-M oiN , TaN , TIN and C r2N ), using in situ X -ray structure determ inations using synchrotron radiation in the diam ond anvil cell. Industry already uses all o f these nitrides as "super-hard" coating m aterials because o f their high hardness properties and their chem ical stability. H ow ever, the volum e com pressibility rem ains unknow n even though it is an im portant param eter.
Compositions based on conductive fillers and synthetic polymer matrices are widely used as adhesives in almost all LED devices. It is glued joints (interfaces) are in major causes become the cause of these devices failures. In the first place this happens in the power switches operating under frequent cyclic on-load operation. The failure probability of the LED module increases exponentially with temperature increase. Reliability of the LED devices operation depends directly on heat dissipation from the chips. In other words, the composition linking the crystals with the DS must have low electric resistivity and good thermomechanical properties.
The measured lifetimes of the devices under test (DUT) can not be modeled with known acceleration models like Arrhenius or Coﬃn Manson, therefore Bayesian Linear Models (LM) are used. The advantages of this method are: (a) available prior knowledge of previously measured data is integrated into the model, so not only current data have an impact on the model parameters. (b) higher ﬂex- ibility and more information in the prediction.
This paper reports the synthetic, characterization and theoretical evaluation of new class of hybrid Heck-immine system involving mixed moieties of vinylene (C=C) and azomethines (CH=N) which has been successfully integrated into an addition of organic semiconducting materials. The assessment of 4-[(hexyloxyphenyl)methylene]amino)-4’-chloro- stilbene (HEXCS) based on Donor (D)-π-Acceptor (A) was evaluated as active semiconductor material candidates via several spectroscopic and analytical techniques. In turn, the investigation of its potential as dopant system in conductive film was successfully deposited on indium tin oxide (ITO) coated substrate via spin coating method. The relationship between electronic and optical properties, chemical modelling at molecular interactions and electrical performances of the designated system were evaluated. In addition, the quantum mechanical calculation proved that the value of energy separation of HEXCS between HOMO and LUMO exhibits 3.09 eV which was in good agreement with the experimental result of optical band gap 3.10 eV. The findings from the thermal and conductivity analysis revealed that the developed film HEXCS exhibited good stability at high temperature and electrical performance with an increasing conductivity up to 0.1531 Scm -1 under maximum light intensity of 100 Wm -2 . Therefore, this proposed type of