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Applied Physics Reviews — 1994


Spectral characteristics of distributed feedback semiconductor lasers and their improvements by corrugation‐pitch‐modulated structure

Makoto Okai

J. Appl. Phys. 75, 1 (1994); http://dx.doi.org/10.1063/1.355884 (29 pages)

Online Publication Date: 12 December 2006

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Semiconductor lasers with stable longitudinal single‐mode operation are essential for optical fiber communication systems. Distributed feedback (DFB) lasers are effective to obtain a stable longitudinal single‐mode operation; however, stability is not enough mainly because of the spatial hole‐burning effect. A corrugation‐pitch‐modulated (CPM) structure was proposed to improve the stability of longitudinal single‐mode operation in distributed feedback lasers. CPM‐DFB lasers have a unique corrugation structure to suppress the spatial hole‐burning effect. This structure was obtained by a newly developed corrugation fabrication method, a photomask self‐interference method. It is confirmed that the CPM‐DFB lasers operate in a stable longitudinal single‐mode by suppressing the spatial hole‐burning effect. This structure is also suitable for narrowing the spectral linewidth for use in coherent optical fiber communication systems. Narrow spectral linewidth lasers with a CPM structure have achieved the narrowest spectral linewidth reported to date.
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42.55.Px Semiconductor lasers; laser diodes
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Thin‐film multilayer interconnect technology for YBa2Cu3O7−x

F. C. Wellstood, J. J. Kingston, and John Clarke

J. Appl. Phys. 75, 683 (1994); http://dx.doi.org/10.1063/1.356469 (20 pages)

Online Publication Date: 12 December 2006

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The construction of microelectronic circuits from high‐transition‐temperature (Tc) superconductors requires techniques for producing thin‐film wires, insulating crossovers, and vias (window contacts) between wires. Together, these three components form a superconducting interconnect technology. The challenges encountered in developing such a technology for high‐Tc superconductors involve factors associated with the materials, the circuits and the fabrication techniques. The use of pulsed laser deposition in conjunction with shadow mask patterning, photolithographic pattern definition, acid etching, ion‐beam etching, and surface cleaning to produce multilayer interconnects from YBa2Cu3O7−x (YBCO) is discussed. These processes have been used to construct a variety of passive high‐temperature superconducting components and circuits, including crossovers, window contacts, multiturn coils, and flux transformers. Integrated magnetometers incorporating superconducting quantum interference devices, multichip modules with semiconductor die bonded to YBCO interconnect structures, and analog‐to‐digital converters have also been successfully demonstrated.
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84.71.Mn Superconducting wires, fibers, and tapes
74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures

Polycrystalline silicon thin films processed with silicon ion implantation and subsequent solid‐phase crystallization: Theory, experiments, and thin‐film transistor applications

Noriyoshi Yamauchi and Rafael Reif

J. Appl. Phys. 75, 3235 (1994); http://dx.doi.org/10.1063/1.356131 (23 pages)

Online Publication Date: 12 December 2006

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A review is presented of the self‐implantation method which has been developed to achieve high‐quality polycrystalline silicon thin films on insulators with enhanced grain sizes and its applications to thin‐film transistors (TFTs). In this method, silicon ions are implanted into an as‐deposited polycrystalline silicon thin film to amorphize most of the film structure. Depending on ion implantation conditions, some seeds with 〈110〉 orientation remain in the film structure due to channeling. The film is then thermally annealed at relatively low temperatures, typically in the range of 550–700 °C. With optimized process conditions, average grain sizes of 1 μm or greater can be obtained. First, an overview is given of the thin‐film transistor technology which has been the greatest motivation for the research and development of the self‐implantation method. Then the mechanism of selective amorphization by the silicon self‐implantation and the crystallization by thermal annealing is discussed. An analytical model and experimental results are described. Polycrystalline silicon TFTs fabricated using the self‐implanted polycrystalline silicon thin‐films are then reviewed. The high‐quality polycrystalline silicon thin films processed with the self‐implantation method results in excellent TFT characteristics for both n‐ and p‐channel devices thereby allowing complementary metal‐oxide‐semiconductor integrated circuits. High mobilities of around 150 cm2/V s for n‐channel TFTs and around 50 cm2/V s for p‐channel TFTs as well as on‐to‐off current ratios of 1×108 have been achieved. Fabrication and characterization of polycrystalline silicon TFTs with channel dimensions comparable to or smaller than the grain size of polycrystalline silicon films are also described to present a case study to discuss the self‐implantation process and associated technologies. Finally, new approaches that extend the self‐implantation method to control grain‐boundary locations are discussed. If grain‐boundary locations can indeed be controlled, the self‐implantation method will become even more valuable in developing future high‐performance TFT integrated circuits.
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61.72.uf Ge and Si
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.30.-z Semiconductor devices

Tentative anatomy of ZnS‐type electroluminescence

E. Bringuier

J. Appl. Phys. 75, 4291 (1994); http://dx.doi.org/10.1063/1.355972 (22 pages)

Online Publication Date: 12 December 2006

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The paper reviews the electrical and optical mechanisms at work in sulfide‐based thin‐film electroluminescence display devices within the framework of general semiconductor physics. The electrical problem is twofold: (i) charge carriers are sourced at high electric field in a nominally insulating material, the carrier density increasing by almost eight orders of magnitude; (ii) the carriers are transported at high field, with an average energy largely exceeding the thermal one. (i) Carrier sourcing is best understood from direct‐current‐driven ZnS films, and is ascribed to partly filled deep donors transferring electrons to the conduction band by Fowler–Nordheim tunneling. The deep donors also act as carrier sinkers, and evidence for space charge is afforded by small‐signal impedance analysis disclosing a markedly inductive behavior. The conduction picture obtained from dc‐driven films is then used to clarify the operation of alternating‐current electroluminescence structures where the sulfide is sandwiched between two blocking oxide layers. The electrostatics of the ac structure is investigated in detail including space charge and field nonuniformity, and external observables are related to internal quantities. The simple model of interfacial carrier sourcing and sinking is examined. (ii) High‐field electronic transport is controlled by the electron‐phonon interaction, and the modeling resorts to numerical simulations or the lucky‐drift concept. At low electron energies the interaction with phonons is predominantly polar, while at optical energies it proceeds via deformation potential scattering.
In spite of the uncertainties in transport models in that range, it is likely that ∼50% of the electrons overtake 2 eV at the usual operating fields in ZnS. Light emission is associated with impurity luminescence centers embedded in the sulfide host. They are excited while current is flowing, and the ensuing relaxation is partly radiative. We describe the two ways in which an impurity may be excited electrically, namely, impact excitation (internal promotion of the center to a state of higher energy) or impact ionization (with an electron released to the host conduction band). The actual excitation mechanism depends on the position of the impurity excited level relative to the host energy bands. A calculation of the excitation yield (number of excited centers per transferred electron) is detailed in the case of impact excitation. Lastly, a phenomenological description of the various relaxation channels is given in terms of formal kinetics, and the relative importance of radiative relaxation is assessed by means of the deexcitation yield (fraction of centers decaying radiatively), which is defined in the case of the impulse response.
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78.60.Fi Electroluminescence
73.50.Fq High-field and nonlinear effects
85.60.Pg Display systems

Photoluminescence of AlxGa1−xAs alloys

Lorenzo Pavesi and Mario Guzzi

J. Appl. Phys. 75, 4779 (1994); http://dx.doi.org/10.1063/1.355769 (64 pages)

Online Publication Date: 12 December 2006

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A thorough discussion of the various features of the photoluminescence spectra of undoped, p‐doped and n‐doped AlxGa1−xAs (0≤x≤1) alloys is given. This review covers spectral features in the energy region ranging from the energy band gap down to ≂0.8 eV, doping densities from isolated impurities to strongly interacting impurities (heavy‐doping effects) and lattice temperatures from 2 to 300 K. The relevance of photoluminescence as a simple but very powerful characterization technique is stressed also in comparison with other experimental methods. The most recent determinations of the Al concentration dependence of some physical properties of the alloy (energy gaps, carrier effective masses, dielectric constants, phonon energies, donor and acceptor binding energies, etc.) are given. The main physical mechanisms of the radiative recombination process in semiconductors are summarized with particular emphasis on the experimental data available for AlxGa1−xAs. The effects of the nature of the band gap (direct or indirect) on the features of the photoluminescence spectra are discussed in detail. Particular attention is devoted to the consequences of the band structure of AlxGa1−xAs (both the multivalley conduction band or the degenerate valence band) on the impurity states by summarizing the theoretical predictions and by detailing the behavior of a number of shallow impurities. Heavy doping effects are also analyzed. A systematic presentation of the photoluminescence related to deep defects and impurities (vacancies, antisites, DX centers, Si‐Si self‐compensating pairs, transition metals, and rare‐earth ions) is carried out after a brief introduction to the terminology used to describe the deep states in semiconductors.
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78.55.Cr III-V semiconductors
71.55.Eq III-V semiconductors
71.35.-y Excitons and related phenomena

Excitonic polaritons in quantum‐confined systems and applications to optoelectronic devices

Toshio Katsuyama and Kensuke Ogawa

J. Appl. Phys. 75, 7607 (1994); http://dx.doi.org/10.1063/1.356592 (19 pages)

Online Publication Date: 12 December 2006

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An excitonic polariton is a complex quasiparticle that consists of a photon and an exciton. Excitonic polaritons have recently been shown to exist in quantum‐confined systems such as GaAs quantum wells. Based on the coherent coupling between the charged electron (hole) and light, the quantum‐confined excitonic polariton has the characteristics of large coherence length and large phase modulation under electric fields. Furthermore, because of the inherent large refractive index, the spatial shape of the guided mode of the excitonic polariton transmitted in such quantum‐confined waveguides is expected to be squeezed significantly. We discuss the characteristics of such excitonic polaritons and possible applications to ultrasmall optoelectronic devices.
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71.35.-y Excitons and related phenomena
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.66.Fd III-V semiconductors

Bolometers for infrared and millimeter waves

P. L. Richards

J. Appl. Phys. 76, 1 (1994); http://dx.doi.org/10.1063/1.357128 (24 pages)

Online Publication Date: 12 December 2006

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This review describes bolometric detectors for infrared and millimeter waves. The introduction sketches the history of modern bolometers, indicates how they fit into the more general class of thermal detectors, and describes the types of applications for which they are the optimum solution. Section I is a tutorial introduction to the elementary theories of bolometer response, of thermal radiation, and of bolometer noise. Important results are derived from the laws of thermal physics in the simplest possible way. The more rigorous theories of bolometer response and noise that are required for quantitative understanding and optimization are then summarized. This material is intended to provide the background required by workers who wish to choose the appropriate bolometer technology for a given measurement, or to evaluate a novel technology. Section II, then describes the various components of an efficient bolometer and gives details of the fabrication and performance of modern bolometers. This discussion focuses on composite bolometers with semiconducting thermometers for operation at and below liquid helium temperatures. The tradeoffs involved in using superconducting thermometers at low temperatures are discussed. Finally, a discussion is given of bolometers for operation at liquid nitrogen temperature which use the new high‐Tc superconductors as thermometers.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.25.Dq Superconducting quantum interference devices (SQUIDs)
FREE

Erratum: ‘‘Novel magnetic applications of high‐Tc bulk superconductors: Lenses for electron beams’’ [J. Appl. Phys. 74, R111 (1993)]

Hidenori Matsuzawa

J. Appl. Phys. 76, 624 (1994); http://dx.doi.org/10.1063/1.357060 (1 page)

Online Publication Date: 12 December 2006

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Abstract Unavailable
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85.25.-j Superconducting devices
99.10.Cd Errata

Large‐band‐gap SiC, III‐V nitride, and II‐VI ZnSe‐based semiconductor device technologies

H. Morkoç, S. Strite, G. B. Gao, M. E. Lin, B. Sverdlov, and M. Burns

J. Appl. Phys. 76, 1363 (1994); http://dx.doi.org/10.1063/1.358463 (36 pages)

Online Publication Date: 12 December 2006

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In the past several years, research in each of the wide‐band‐gap semiconductors, SiC, GaN, and ZnSe, has led to major advances which now make them viable for device applications. The merits of each contender for high‐temperature electronics and short‐wavelength optical applications are compared. The outstanding thermal and chemical stability of SiC and GaN should enable them to operate at high temperatures and in hostile environments, and also make them attractive for high‐power operation. The present advanced stage of development of SiC substrates and metal‐oxide‐semiconductor technology makes SiC the leading contender for high‐temperature and high‐power applications if ohmic contacts and interface‐state densities can be further improved. GaN, despite fundamentally superior electronic properties and better ohmic contact resistances, must overcome the lack of an ideal substrate material and a relatively advanced SiC infrastructure in order to compete in electronics applications. Prototype transistors have been fabricated from both SiC and GaN, and the microwave characteristics and high‐temperature performance of SiC transistors have been studied. For optical emitters and detectors, ZnSe, SiC, and GaN all have demonstrated operation in the green, blue, or ultraviolet (UV) spectra.
Blue SiC light‐emitting diodes (LEDs) have been on the market for several years, joined recently by UV and blue GaN‐based LEDs. These products should find wide use in full color display and other technologies. Promising prototype UV photodetectors have been fabricated from both SiC and GaN. In laser development, ZnSe leads the way with more sophisticated designs having further improved performance being rapidly demonstrated. If the low damage threshold of ZnSe continues to limit practical laser applications, GaN appears poised to become the semiconductor of choice for short‐wavelength lasers in optical memory and other applications. For further development of these materials to be realized, doping densities (especially p type) and ohmic contact technologies have to be improved. Economies of scale need to be realized through the development of larger SiC substrates. Improved substrate materials, ideally GaN itself, need to be aggressively pursued to further develop the GaN‐based material system and enable the fabrication of lasers. ZnSe material quality is already outstanding and now researchers must focus their attention on addressing the short lifetimes of ZnSe‐based lasers to determine whether the material is sufficiently durable for practical laser applications. The problems related to these three wide‐band‐gap semiconductor systems have moved away from materials science toward the device arena, where their technological development can rapidly be brought to maturity.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
85.30.-z Semiconductor devices
85.60.-q Optoelectronic devices
42.70.Hj Laser materials

Heavy‐ion sources for radiation therapy

Y. Sato, A. Kitagawa, H. Ogawa, and S. Yamada

J. Appl. Phys. 76, 3947 (1994); http://dx.doi.org/10.1063/1.357411 (23 pages)

Online Publication Date: 12 December 2006

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The usefulness of particle beams for radiation therapy has been well and widely recognized. For the cure of cancer patients, many accelerator facilities have already been utilized, and some new facilities are now being put into operation, or are under construction. Considering the medical and biological requirements, light heavy ions with an energy of several hundred MeV/nucleon are regarded as being the most suitable species. A reasonable choice to this end is an accelerator complex, for an example, one comprising an ion source, an injector linac, and a synchrotron. The ion source is of great importance, since its characteristics strongly affect the overall performance of the accelerator system. A pulsed Penning source (PIGIS) has been successfully used at Lawrence Berkeley Laboratory. Recently, at the National Institute of Radiological Sciences a low‐duty pulsed PIGIS for the heavy‐ion medical accelerator in Chiba (HIMAC) has been developed; it has both a long lifetime and a high peak intensity. As other types of ion sources, an electron‐beam ion source (EBIS) and an electron‐cyclotron‐resonance ion source (ECRIS) are being developed at several laboratories. An EBIS is basically a pulsed source, and is being successfully used at Saclay. By using an after‐glow mode, two ECRISs have made remarkable progress at Grenoble and the Grand Accelerateur National d’Ions Lourds; similar tests are proceeding for the Schwer‐Ionen Synchrotron at the Gesellschaft für Schwer‐Ionenforschung, the booster at Centre d’Europeen de Recherche Nucleaire, and the HIMAC. These different types of heavy‐ion sources are discussed from the viewpoint of their application to radiation therapy.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
87.56.B- Radiation sources

Characterization of defects in Si and SiO2−Si using positrons

P. Asoka‐Kumar, K. G. Lynn, and D. O. Welch

J. Appl. Phys. 76, 4935 (1994); http://dx.doi.org/10.1063/1.357207 (48 pages)

Online Publication Date: 12 December 2006

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In the past few years, there has been rapid growth in the positron annihilation spectroscopy (PAS) of overlayers, interfaces, and buried regions of semiconductors. There are few other techniques that are as sensitive as PAS to low concentrations of open‐volume‐type defects. The characteristics of the annihilation gamma rays depend strongly on the local environment of the annihilation sites and are used to probe defect concentrations in a range inaccessible to conventional defect probes, yet which are important in the electrical performance of device structures. We show how PAS can be used as a nondestructive probe to examine defects in technologically important Si‐based structures. The discussion will focus on the quality of overlayers, formation and annealing of defects after ion implantation, identification of defect complexes, and evaluation of the distribution of internal electric fields. We describe investigations of the activation energy for the detrapping of hydrogen from SiO2−Si interface trap centers, variations of interface trap density, hole trapping at SiO2−Si interfaces, and radiation damage in SiO2−Si systems. We also briefly summarize the use of PAS in compound semiconductor systems and suggest some future directions.
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61.72.-y Defects and impurities in crystals; microstructure
71.55.-i Impurity and defect levels
78.70.Bj Positron annihilation

Oxygen diffusion in cuprate superconductors

J. L. Routbort and S. J. Rothman

J. Appl. Phys. 76, 5615 (1994); http://dx.doi.org/10.1063/1.357067 (14 pages)

Online Publication Date: 12 December 2006

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Superconducting properties of the cuprate superconductors depend on the oxygen content of the material; the diffusion of oxygen is thus an important process in the fabrication and application of these materials. In the present article, we review studies of the diffusion of oxygen in La2−xSrxCuO4, YBa2Cu3O7−δ, YBa2Cu4O8, and the Bi2Sr2Can−1CunO2n+4 (n=1 or 2) superconductors, and attempt to elucidate the atomic mechanisms responsible.  
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74.62.Dh Effects of crystal defects, doping and substitution
74.72.-h Cuprate superconductors
66.30.-h Diffusion in solids
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