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Applied Physics Reviews — 2006

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Degradation of hexagonal silicon-carbide-based bipolar devices

M. Skowronski and S. Ha

J. Appl. Phys. 99, 011101 (2006); http://dx.doi.org/10.1063/1.2159578 (24 pages)

Online Publication Date: 13 January 2006

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Only a few years ago, an account of degradation of silicon carbide high-voltage p-i-n diodes was presented at the European Conference on Silicon Carbide and Related Compounds (Kloster Banz, Germany, 2000). This report was followed by the intense effort of multiple groups utilizing varied approaches and subsequent progress in both fundamental understanding of this phenomenon and its elimination. The degradation of SiC p-i-n junctions is now well documented to be due to the expansion of Shockley-type stacking faults in the part of the devices reached by the electron-hole plasma. The faults can gradually cover most of the junction area, impeding current flow and, as a result, increasing the on-state resistance. While in most semiconductors stacking faults are electrically inactive, in hexagonal silicon carbide polytypes (4H- and 6H-SiC) they form quantum-well-like electron states observed in luminescence and confirmed by first-principles calculations. The stacking-fault expansion occurs via motion of 30° silicon-core partial dislocations. The Si–Si bond along the dislocation line induces a deep level in the SiC band gap. This state serves as both a radiative and a nonradiative recombination center and converts the electron-hole recombination energy into activation energy for the dislocation motion. Dislocation motion is typically caused by shear stress, but in the case of SiC diodes, the driving force appears to be intrinsic to the material or to the fault itself, i.e., the fault expansion appears to lower the energy of the system. Stable devices can be fabricated by eliminating stacking-fault nucleation sites. The dominant type of such preexisting defects is the segment of basal plane dislocations dissociated into partials. The density of such defects can be reduced to below 1 cm−2 by conversion of all basal plane dislocations propagating from the substrate into threading ones in the epitaxial layer. Remarkable progress in fabrication of low basal plane dislocation density material offers hope of bipolar SiC devices being available commercially in the near future.
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85.30.Kk Junction diodes
85.30.Pq Bipolar transistors
61.72.Nn Stacking faults and other planar or extended defects
71.55.Ht Other nonmetals
61.72.Lk Linear defects: dislocations, disclinations

Adhesive wafer bonding

F. Niklaus, G. Stemme, J. -Q. Lu, and R. J. Gutmann

J. Appl. Phys. 99, 031101 (2006); http://dx.doi.org/10.1063/1.2168512 (28 pages)

Online Publication Date: 9 February 2006

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Wafer bonding with intermediate polymer adhesives is an important fabrication technique for advanced microelectronic and microelectromechanical systems, such as three-dimensional integrated circuits, advanced packaging, and microfluidics. In adhesive wafer bonding, the polymer adhesive bears the forces involved to hold the surfaces together. The main advantages of adhesive wafer bonding include the insensitivity to surface topography, the low bonding temperatures, the compatibility with standard integrated circuit wafer processing, and the ability to join different types of wafers. Compared to alternative wafer bonding techniques, adhesive wafer bonding is simple, robust, and low cost. This article reviews the state-of-the-art polymer adhesive wafer bonding technologies, materials, and applications.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
61.41.+e Polymers, elastomers, and plastics
01.30.Rr Surveys and tutorial papers; resource letters

Flat panel displays for ubiquitous product applications and related impurity doping technologies

Toshiharu Suzuki

J. Appl. Phys. 99, 111101 (2006); http://dx.doi.org/10.1063/1.2199753 (15 pages)

Online Publication Date: 1 June 2006

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Various kinds of flat panel displays such as liquid crystal displays (LCDs), plasma display panels and organic light emitting diode (OLED) displays are briefly evaluated from the perspective of applicability to ubiquitous products. It is clarified that the LCDs and OLED displays are suitable for realizing mobile electronic products with a high quality display, since these displays can use active devices on the backplanes to form active matrix displays and can integrate peripheral circuits of the displays and functional circuits of mobile electronics for a ubiquitous era. It is clarified further that the low temperature polycrystalline silicon (LTPS) thin film transistor (TFT) is the most promising active device for the backplane of such active matrix displays because the LTPS TFT has the possibility to enhance its performance without raising the cost. The low temperature poly-Si TFT fabrication process is introduced, and its key technologies such as crystallization, gate oxide formation, and impurity doping are surveyed. As the property of polycrystalline silicon (poly-Si) influences not only the TFT performance itself but also the efficiency of impurity doping and the integrity of the gate oxide, the crystallinity of the poly-Si is reviewed. After that, the history of the development and the state of the art in impurity doping technology and its issues are addressed in detail. Finally, foreseeing the application of LTPS TFT, the realization of OLED displays, and the progress of LTPS TFT for integrating higher functional circuits for ubiquitous applications, the requirements for impurity doping in such progress are addressed. In particular, the single grain silicon technology and the scaling down of the TFT size, which are thought to be highly effective to enhance the performance of TFTs, and issues of impurity doping technology relating to them are discussed.
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85.60.Pg Display systems
85.30.Tv Field effect devices
85.60.Jb Light-emitting devices
42.79.Kr Display devices, liquid-crystal devices
61.72.uf Ge and Si
01.30.Rr Surveys and tutorial papers; resource letters
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Epitaxial growth and optical properties of semiconductor quantum wires

Xue-Lun Wang and Valia Voliotis

J. Appl. Phys. 99, 121301 (2006); http://dx.doi.org/10.1063/1.2212056 (38 pages)

Online Publication Date: 28 June 2006

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In this paper we present a review on major advances achieved over the past ten years in the field of fabrication of semiconductor quantum wires (QWRs) using epitaxial growth techniques and investigation of their optical properties. We begin the review with a brief summary on typical epitaxial QWRs developed so far. We next describe the state-of-the-art structural qualities of epitaxial QWRs in terms of (i) size uniformity between wires, (ii) heterointerface uniformity, (iii) crystal purity, and (iv) strength of lateral quantum confinement. Several prominent breakthroughs have been accomplished concerning the improvements of wire qualities, including (i) realization of V-shaped GaAs/AlGaAs QWRs in the “real one-dimensional” (1D) regime in which exciton states can extend coherently over distances exceeding 1 μm, (ii) reduction of residual impurity concentrations in V-shaped GaAs/AlGaAs QWRs to a level comparable to that in an equivalent quantum well (QWL), which resulted in the semiconductor QWR with room-temperature photoluminescence efficiency exceeding that of a QWL, and (iii) reduction of the multimonolayer (ML) interface fluctuations on the second-grown arm QWL surface, in old-generation T-shaped GaAs/AlGaAs QWRs, to the single-ML level. The second part of this article is devoted to the discussion of optical properties of epitaxial QWRs, such as exciton dynamics, fine structure of exciton levels, and nonlinear effects, studied by means of high-spatial resolution spectroscopy, i.e., microphotoluminescence experiments. We will concentrate our discussions on V-shaped GaAs/AlGaAs QWRs and put an emphasis on demonstrating how the interface quality influences wire’s optical properties. The properties of QWRs in the “zero-dimensional quantum box regime” and QWRs in the real 1D regime will be presented in separate sections. We will show that the realization of QWRs in the real 1D regime makes possible the investigation of intrinsic 1D effects by focusing on a single perfect 1D wire region using microscopic techniques. This has led to important results, for instance, (i) the demonstration of the square-root dependence of 1D exciton radiative recombination lifetimes down to a temperature as low as 10 K (limited by the experimental setup) and (ii) the clear demonstration of the existence of Mott transition in a 1D exciton system which is a fundamental problem under long debate.
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68.65.La Quantum wires (patterned in quantum wells)
81.10.-h Methods of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
78.67.Lt Quantum wires
71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors
71.30.+h Metal-insulator transitions and other electronic transitions

Constructal theory of generation of configuration in nature and engineering

Adrian Bejan and Sylvie Lorente

J. Appl. Phys. 100, 041301 (2006); http://dx.doi.org/10.1063/1.2221896 (27 pages)

Online Publication Date: 29 August 2006

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Constructal theory is the view that the generation of flow configuration is a physics phenomenon that can be based on a physics principle (the constructal law): “For a finite-size flow system to persist in time (to survive) its configuration must evolve in such a way that it provides an easier access to the currents that flow through it” [A. Bejan, Advanced Engineering Thermodynamics, 2nd ed. (Wiley, New York, 1997); Int. J. Heat Mass Transfer, 40, 799 (1997)]. This principle predicts natural configuration across the board: river basins, turbulence, animal design (allometry, vascularization, locomotion), cracks in solids, dendritic solidification, Earth climate, droplet impact configuration, etc. The same principle yields new designs for electronics, fuel cells, and tree networks for transport of people, goods, and information. This review describes a paradigm that is universally applicable in natural sciences, engineering and social sciences.
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47.85.-g Applied fluid mechanics
47.10.-g General theory in fluid dynamics
47.27.-i Turbulent flows
47.55.D- Drops and bubbles
87.19.rs Movement
87.19.ru Locomotion
01.30.Rr Surveys and tutorial papers; resource letters

Diffusion in alumina

Robert H. Doremus

J. Appl. Phys. 100, 101301 (2006); http://dx.doi.org/10.1063/1.2393012 (17 pages)

Online Publication Date: 30 November 2006

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Experimental results on diffusion in alumina are summarized and critically discussed. The most reliable results are those on volume diffusion in single crystals (sapphire), and are available for a wide variety of substances, including the structural elements oxygen and alumina, water, monovalent cations, and trivalent cations. Experimental results on volume diffusion in polycrystalline alumina have also been reported for hydrogen, water, some actinides, and rare earths. Diffusion coefficients have been deduced from deep penetration tails on diffusion profiles, and have been interpreted to result from fast diffusion along dislocations or grain boundaries. However, there are questions about these interpretations that are discussed. Mechanisms of diffusion in alumina are uncertain; a variety of charged defects has been suggested to control diffusion in alumina, but no interpretation is widely accepted because of discrepancies with experimental results. The possibility of an AlO defect is put forward to stimulate exploration and discussions; together with a diffusion-reaction mechanism, it can explain many puzzling features of diffusion in alumina. The electrical conductivity of alumina results from the transport of H+(H3O+) ions if the OH concentration in the alumina is greater than about 3×10−7 OH groups per Al atom. At lower OH concentrations electronic conductivity becomes dominant.
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66.30.Lw Diffusion of other defects
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Mm Grain and twin boundaries
72.80.Sk Insulators
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