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15 Apr 2003

Volume 93, Issue 8, pp. 4355-4942

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Quantum well photoconductors in infrared detector technology

A. Rogalski

J. Appl. Phys. 93, 4355 (2003); http://dx.doi.org/10.1063/1.1558224 (37 pages) | Cited 36 times

Online Publication Date: 28 March 2003

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The paper compares the achievements of quantum well infrared photodetector (QWIP) technology with those of competitive technologies, with the emphasis on the material properties, device structure, and their impact on focal plane array (FPA) performance. Special attention is paid to two competitive technologies, QWIP and HgCdTe, in the long-wavelength IR (LWIR) and very-long-wavelength IR (VLWIR) spectral ranges. Because so far, the dialogue between the QWIP and HgCdTe communities is limited, the paper attempts to settle the main issues of both technologies. Such an approach, however, requires the presentation of fundamental limits to the different types of detectors, which is made at the beginning. To write the paper more clearly for readers, many details are included in the Appendix. In comparative studies both photon and thermal detectors are considered. Emphasis is placed on photon detectors. In this group one may distinguish HgCdTe photodiodes, InSb photodiodes, and doped silicon detectors. The potential performance of different materials as infrared detectors is examined utilizing the α/G ratio, where α is the absorption coefficient and G is the thermal generation rate. It is demonstrated that LWIR QWIP’s cannot compete with HgCdTe photodiodes as single devices, especially at higher operating temperatures (>70 K). This is due to the fundamental limitations associated with intersubband transitions. The advantage of HgCdTe is, however, less distinct at temperatures lower than 50 K due to problems inherent in the HgCdTe material (p-type doping, Shockley–Read recombination, trap-assisted tunneling, surface and interface instabilities). Even though QWIP is a photoconductor, several of its properties, such as high impedance, fast response time, long integration time, and low power consumption, comply well with the requirements imposed on the fabrication of large FPA’s. Due to a high material quality at low temperatures, QWIP has potential advantages over HgCdTe in the area of VLWIR FPA applications in terms of array size, uniformity, yield, and cost of the systems. The performance figures of merit of state-of-the-art QWIP and HgCdTe FPA’s are similar because the main limitations come from the readout circuits. Performance is, however, achieved with very different integration times. The choice of the best technology is therefore driven by the specific needs of a system. In the case of readout-limited detectors a low photoconductive gain increases the signal-to-noise ratio and a QWIP FPA can have a better noise equivalent difference temperature than an HgCdTe FPA with a charge well of similar size. Both HgCdTe photodiodes and QWIP’s offer multicolor capability in the MWIR and LWIR range. Powerful possibilities offered by QWIP technology are associated with VLWIR FPA applications and with multicolor detection. The intrinsic advantage of QWIP’s in this niche is due to the relative ease of growing multicolor structures with a very low defect density. © 2003 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Dw Photodiodes; phototransistors; photoresistors
01.30.Rr Surveys and tutorial papers; resource letters
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
73.63.Hs Quantum wells
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Photoinduced magnetic uniaxial anisotropy and molecular orientation of polymer containing azobenzene side groups with free radical end

Z. D. Xu, X. F. Chen, X. H. Fan, X. H. Wan, and Q. F. Zhou

J. Appl. Phys. 93, 4392 (2003); http://dx.doi.org/10.1063/1.1559634 (3 pages)

Online Publication Date: 28 March 2003

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A polymer containing azobenzene side groups each with an organic free radical end was synthesized. Before irradiation by an Ar+ laser beam, the polymer was magnetically isotropic. However, with the irradiation of a polarized Ar+ laser beam, the photoisomerization and reorientation of the azobenzenes took place bringing about a magnetic anisotropy in the radical containing polymer film. The magnetic anisotropy was studied by using a superconducting quantum interference device. It was found that when the applied magnetic field H≈1 Oe, the magnetization Mz(H) in the direction perpendicular to the polymer film was 3.63×10−4 emu/g, while those parallel to the polymer film were Mx(H)=My(H)=−1.1×10−5 emu/g. © 2003 American Institute of Physics.
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75.30.Gw Magnetic anisotropy
75.50.Xx Molecular magnets
82.35.-x Polymers: properties; reactions; polymerization
82.30.Qt Isomerization and rearrangement
82.50.Hp Processes caused by visible and UV light
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology

Antireflection coatings from analogy between electron scattering and spin precession

D. W. L. Sprung, Gregory V. Morozov, and J. Martorell

J. Appl. Phys. 93, 4395 (2003); http://dx.doi.org/10.1063/1.1559942 (12 pages) | Cited 3 times

Online Publication Date: 28 March 2003

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We use the analogy between scattering of a wave from a potential, and the precession of a spin-half particle in a magnetic field, to gain insight into the design of an antireflection coating for electrons in a semiconductor superlattice. It is shown that the classic recipes derived for optics are generally not applicable due to the different dispersion law for electrons. Using the stability conditions we show that a Poisson distribution of impedance steps is a better approximation than is a Gaussian distribution. Examples are given of filters with average transmissivity exceeding 95% over an allowed band. © 2003 American Institute of Physics.
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41.85.-p Beam optics
42.79.Wc Optical coatings
42.15.Eq Optical system design
02.50.Ng Distribution theory and Monte Carlo studies

Optical wire-grid polarizers at oblique angles of incidence

X. J. Yu and H. S. Kwok

J. Appl. Phys. 93, 4407 (2003); http://dx.doi.org/10.1063/1.1559937 (6 pages) | Cited 52 times

Online Publication Date: 28 March 2003

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Nanotechnology enables the fabrication of wire-grid polarizers (WGP) in the visible optical region. At oblique angles of incidence, WGP can be used as polarizing beam splitters (PBS). As such, they have the advantages of large numerical aperture and high-extinction ratios in both transmission and reflection. Because of these properties, WGP is being explored as PBS replacement in projectors. In this article, we present a complete theoretical investigation of the WGP. Rigorous diffraction theory, exact lowest-order eigenmode effective-media theory, and form birefringence theory are discussed. These theories are compared with experimental measurement of T(θ) and R(θ) as a function of the polarization state of the input light and as a function of the incident angle θ. It is shown that only the rigorous diffraction theory can fit the data for all incident angles. Using diffraction theory we provide a calculation relating the optical properties of the WGP to the physical dimensions of the wire grids. Thus, a framework for optimizing the optical properties of the WGP for various applications and requirements is provided. © 2003 American Institute of Physics.
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42.79.Ci Filters, zone plates, and polarizers
42.79.Fm Reflectors, beam splitters, and deflectors
42.25.Fx Diffraction and scattering
42.25.Lc Birefringence
78.20.Fm Birefringence

Polymer electrophosphorescent devices utilizing a ladder-type poly(para-phenylene) host

X. H. Yang, D. Neher, U. Scherf, S. A. Bagnich, and H. Bässler

J. Appl. Phys. 93, 4413 (2003); http://dx.doi.org/10.1063/1.1562002 (7 pages) | Cited 10 times

Online Publication Date: 28 March 2003

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The properties of light-emitting diodes based on the electrophorescent platinum-porphyrin dye PtOEP blended into a ladder-type poly(para-phenylene) (LPPP) polymer host are presented. Due to the small difference between the highest occupied molecular orbital (HOMO) levels of the guest and the host, the operating voltage of single layer devices is almost independent of the dopant concentration in clear contrast to what has been observed in the case of wide-band gap host polymers. However, the efficiency and the color purity of these single-layer devices is quite poor, which can be attributed to the weak trapping of carriers on the phosphorescent dye. Incorporating an electron-transporting/hole-blocking layer greatly increases the efficiency of the devices but at the same time emission from the host becomes more significant. Adding a hole-transporting/electron-blocking layer further increases the efficiency of the devices. Pure red emission is, however, only obtained if the HOMO of the hole-transporting layer is well above that of the LPPP host. This effect is interpreted in terms of a direct injection of holes from the hole-transporting layer into the HOMO level of the dopant. Further, prompt fluorescence and phosphorescence studies indicate that energy transfer from LPPP singlet excitons contributes to the emission from the dopant, but that the efficiency of singlet exciton transfer is too small to explain the almost complete absence of host emission in the electroluminescence spectra of single- and three-layer devices. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
82.35.Cd Conducting polymers
78.55.Kz Solid organic materials
82.35.Jk Copolymers, phase transitions, structure
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Simulation of sheath dynamics and current nonuniformity in plasma-immersion ion implantation of a patterned surface

Boris Briehl and Herbert M. Urbassek

J. Appl. Phys. 93, 4420 (2003); http://dx.doi.org/10.1063/1.1555682 (12 pages) | Cited 6 times

Online Publication Date: 28 March 2003

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We study the steady-state structure and the dynamics of a plasma sheath surrounding a patterned surface. A two-dimensional hybrid particle-in-cell code is employed where special attention is given to the plasma side boundaries. The surface consists of a periodic array of wide and narrow trenches. We characterize the conformity of the steady-state sheath and the uniformity of the ion currents to the wall as well as the sheath-expansion dynamics following sudden negative charging of the surface. We study the nonuniform motion of the sheath edge away from the surface, which leads to a planar high-voltage sheath. The inhomogeneous distributions of ion current and impact angle onto the walls are discussed.© 2003 American Institute of Physics.
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61.72.up Other materials
81.65.Ps Polishing, grinding, surface finishing
52.40.Kh Plasma sheaths
52.65.Rr Particle-in-cell method
52.77.Dq Plasma-based ion implantation and deposition

Gas temperature measurement in CH4/CO2 dielectric-barrier discharges by optical emission spectroscopy

Jorge Luque, Martin Kraus, Alexander Wokaun, Ken Haffner, Ulrich Kogelschatz, and Baldur Eliasson

J. Appl. Phys. 93, 4432 (2003); http://dx.doi.org/10.1063/1.1560570 (7 pages) | Cited 10 times

Online Publication Date: 28 March 2003

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The gas temperatures were determined by optical emission in a dielectric-barrier discharge at atmospheric pressure. The feed gases were either pure CH4 to yield higher hydrocarbons or CH4/CO2 mixtures to yield synthesis gas (H2/CO). The monitored emission was from the CH radical A 2Δ–X 2Π electronic system and the gas temperature range characterized was from 300 to 600 K. The technique described in this article enables the measurement of the neutral gas temperature in the discharge that is not accessible via conventional methodology using thermocouples. A bimodal rotational population distribution in the CH A 2Δ v′=0 state was determined in the investigated gas mixtures of CO2/CH4 and in pure methane. Most of the rotational population was at temperatures from 300 to 600 K depending on experimental conditions, which are only slightly higher than the set temperature of the reactor. A small fraction of the emitting species was found to have a much higher rotational temperature of ∼4000 K for the pure methane gas and the mixture of CO2 and CH4. The low temperature rotational distribution correlated with changes in the ambient conditions and is used as a thermometer, while the high rotational temperature component and the vibrational temperature reflect the excess of energy during the CH radical formation by electron impact dissociative excitation of methane, and the extent of collisional relaxation before emission takes place. © 2003 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.-s Electric discharges
52.25.Mq Dielectric properties
52.25.Kn Thermodynamics of plasmas
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Electron-beam irradiation of porous silicon: Application to micromachining

Stefano Borini, Giampiero Amato, Massimiliano Rocchia, Luca Boarino, and Andrea Mario Rossi

J. Appl. Phys. 93, 4439 (2003); http://dx.doi.org/10.1063/1.1560853 (3 pages) | Cited 8 times

Online Publication Date: 28 March 2003

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Results on electron irradiation of porous silicon are presented and discussed. An electron-beam lithography system is used to irradiate small surface portions of porous silicon, without the use of any sensitive resists. In this way, it has been possible to write pattern with lateral resolution down to 120 nm. It is suggested that direct exposure to electron irradiation provokes the formation of defects, with an enhanced reactivity of exposed areas. This effect is suggested as a possible way to micro- and nanostructuring of porous silicon. © 2003 American Institute of Physics.
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61.80.Fe Electron and positron radiation effects
81.05.Cy Elemental semiconductors
81.05.Rm Porous materials; granular materials
61.82.Fk Semiconductors
81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer
81.20.Wk Machining, milling

Reflection anisotropy spectroscopy: A probe of rubbed polyimide liquid crystal alignment layers

B. F. Macdonald, W. Zheng, and R. J. Cole

J. Appl. Phys. 93, 4442 (2003); http://dx.doi.org/10.1063/1.1559423 (5 pages) | Cited 10 times

Online Publication Date: 28 March 2003

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The prospect of using reflectance anisotropy spectroscopy (RAS) for process control in the fabrication of liquid crystal devices is investigated. Measurements of the optical anisotropy induced by mechanically rubbing polymer thin films are presented and interpreted in terms of molecular alignment and form birefringence models. Optical characterization of completed liquid crystal cells enables RAS measurements to be correlated with device characteristics. © 2003 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Fm Birefringence
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
42.70.Df Liquid crystals

Calorimetric and x-ray analysis of the intermediate phase formation in Cu/Mg multilayers

J. Rodríguez-Viejo, M. Gonzalez-Silveira, and M. T. Clavaguera-Mora

J. Appl. Phys. 93, 4447 (2003); http://dx.doi.org/10.1063/1.1557782 (7 pages) | Cited 3 times

Online Publication Date: 28 March 2003

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The kinetics of intermediate phase formation in (20 nm) Cu/(80 nm) Mg multilayers is analyzed using differential scanning calorimetry (DSC) and in situ x-ray diffraction. The as-prepared Mg layers are polycrystalline with large grain sizes and a columnar structure which gives a preferred orientation along the (0002) direction. On the contrary, the Cu films are nanocrystalline with average nanocrystal populations of different sizes. The continuos scan DSC traces show three main exothermic peaks. The first two reactions are significantly overlapped. We find both processes are related to nucleation and growth of the Mg2Cu along the interface and present an explanation based on the different roughness of the nc-Cu on Mg and the Mg on nc-Cu interfaces. The third exothermic reaction is due to the growth of the Mg2Cu perpendicular to the original interface. A kinetic model is developed which yields calculated calorimetric traces in very good agreement with the experimental data. The model includes two independent nucleation & growth mechanisms. A soft-diffusion control of the one-dimensional thickening of the Mg2Cu product phase is included to account for the gradual decrease associated to the end of the third calorimetric peak. © 2003 American Institute of Physics.
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68.65.Ac Multilayers
68.35.Fx Diffusion; interface formation

Effect of heat and film thickness on a photoinduced phase transition in azobenzene liquid crystalline polyesters

C. Sánchez, R. Alcalá, S. Hvilsted, and P. S. Ramanujam

J. Appl. Phys. 93, 4454 (2003); http://dx.doi.org/10.1063/1.1560852 (7 pages) | Cited 11 times

Online Publication Date: 28 March 2003

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The liquid crystal to isotropic phase transition induced with 488 nm light in films of liquid crystalline azobenzene polyesters has been studied as a function of temperature, light intensity, and film thickness. That phase transition is associated with the photoinduced trans–cis–trans isomerizations of azobenzene molecules and it has been found that the 488 nm light power needed to induce the transition to the isotropic state increases when the film thickness decreases. The irradiation with the laser beam heats the film up and this seems to be responsible for the observed thickness dependence. Optical absorption measurements show that azobenzene aggregates present in one of the polymers are broken down in the photoinduced phase transition. The birefringence induced with low power 488 nm light in films before and after undergoing that photoinduced phase transition has also been studied. Birefringence shows a faster growing rate in films which have undergone the transition. © 2003 American Institute of Physics.
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64.70.M- Transitions in liquid crystals
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
82.50.Hp Processes caused by visible and UV light
61.82.Pv Polymers, organic compounds
61.41.+e Polymers, elastomers, and plastics
68.55.-a Thin film structure and morphology
78.66.Qn Polymers; organic compounds
61.30.Vx Polymer liquid crystals
82.30.Qt Isomerization and rearrangement
78.20.Fm Birefringence
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Optoelectronic properties of thick SiGe layers grown as small mesas by low pressure chemical vapor deposition

T. Stoica and L. Vescan

J. Appl. Phys. 93, 4461 (2003); http://dx.doi.org/10.1063/1.1559636 (7 pages) | Cited 6 times

Online Publication Date: 28 March 2003

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Arrays of Si0.80Ge0.20/Si(001) square mesas were epitaxially grown by low pressure chemical vapor deposition to optimize the light emission in the near infrared range. To study the influence of mesa size on light emission the current–voltage characteristics, the spectral photocurrent, and the electroluminescence of p-i-n structures were measured. While the plastic relaxation has a strong influence on the electroluminescence spectra, the current–voltage characteristics are only slightly changed. At low temperatures, a tunneling current was observed and its possible location is discussed. Due to the high SiGe thickness, both the contributions of the no-phonon and transversal optical phonon-assisted transitions to the photocurrent spectra could be observed. Direct evidence of the higher band gap of relaxed SiGe was obtained from electroluminescence studies. © 2003 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
79.60.-i Photoemission and photoelectron spectra
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.60.Fi Electroluminescence

Influence of cap layer on implantation induced interdiffusion in InP/InGaAs quantum wells

C. Carmody, H. H. Tan, and C. Jagadish

J. Appl. Phys. 93, 4468 (2003); http://dx.doi.org/10.1063/1.1555273 (3 pages) | Cited 8 times

Online Publication Date: 28 March 2003

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We have investigated the effect of implantation at room temperature and 200 °C into lattice matched InP/InGaAs quantum well structures capped with InP and InGaAs layers. P− ions of 20 keV were implanted into the cap layer at doses of 1×1012−1×1014 cm−2. The dose dependent evolution of shifts in photoluminescence energy for the InP capped sample was found to be affected by the implant temperature. Rutherford back scattering measurements show that the nature of the damage induced at different implant temperatures is responsible for this behavior. It was found that the InGaAs capped sample was less sensitive to the implant temperature than the InP capped sample. © 2003 American Institute of Physics.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
68.65.Fg Quantum wells
61.72.uj III-V and II-VI semiconductors
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Photonic band-gap effects on photoluminescence of silicon nanocrystals embedded in artificial opals

J. Valenta, J. Linnros, R. Juhasz, J.-L. Rehspringer, F. Huber, C. Hirlimann, S. Cheylan, and R. G. Elliman

J. Appl. Phys. 93, 4471 (2003); http://dx.doi.org/10.1063/1.1560565 (4 pages) | Cited 12 times

Online Publication Date: 28 March 2003

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Si nanocrystals were formed in synthetic opals by Si-ion implantation and their optical properties studied using microphotoluminescence and reflection techniques. The properties of areas with high crystalline quality are compared with those of disordered regions of samples. The photoluminescence spectrum from Si nanocrystals embedded in silica spheres is narrowed by the inhibition of emission at wavelengths corresponding to the opal photonic pseudoband gap (∼690 nm). Measurements of photoluminescence spectra from individual implanted silica spheres is also demonstrated and the number of emitting Si nanocrystals in single brightly emitting spheres is estimated to be of the order of one thousand. © 2003 American Institute of Physics.
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78.55.Ap Elemental semiconductors
42.70.Qs Photonic bandgap materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.20.Ps Other inorganic compounds
71.20.Mq Elemental semiconductors
71.55.Ht Other nonmetals
81.05.Cy Elemental semiconductors
61.72.up Other materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.50.-p Quantum optics
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials

Effect of temperature on the optical properties of GaAsSbN/GaAs single quantum wells grown by molecular-beam epitaxy

S. A. Lourenço, I. F. L. Dias, L. C. Poças, J. L. Duarte, J. B. B. de Oliveira, and J. C. Harmand

J. Appl. Phys. 93, 4475 (2003); http://dx.doi.org/10.1063/1.1560574 (5 pages) | Cited 22 times

Online Publication Date: 28 March 2003

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GaAsSbN/GaAs strained-layer single quantum wells grown on a GaAs substrate by molecular-beam epitaxy with different N concentrations were studied using the photoluminescence (PL) technique in the temperature range from 9 to 296 K. A strong redshift in optical transition energies induced by a small increase in N concentration has been observed in the PL spectra. This effect can be explained by the interaction between a narrow resonant band formed by the N-localized states and the conduction band of the host semiconductor. Excitonic transitions in the quantum wells show a successive red/blue/redshift with increasing temperature in the 2–100 K range. The activation energies of nonradiative channels responsible for a strong thermal quenching are deduced from an Arrhenius plot of the integrated PL intensity. © 2003 American Institute of Physics.
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78.67.De Quantum wells
81.07.St Quantum wells
78.55.Cr III-V semiconductors
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
73.21.Fg Quantum wells
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Cross-sectional transmission electron microscopy study of the influence of niobium on the formation of titanium silicide in small-feature contacts

T. Jarmar, J. Seger, F. Ericson, U. Smith, and S.-L. Zhang

J. Appl. Phys. 93, 4480 (2003); http://dx.doi.org/10.1063/1.1555270 (5 pages) | Cited 1 time

Online Publication Date: 28 March 2003

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The influence of a Nb layer between Si and Ti on the formation of TiSi2 in small-feature contacts and of the substrate doping level has been studied using transmission electron microscopy in combination with convergent-beam electron diffraction. For an As dose of 2.5×1016 cm−2, a mixture of C49 and partially agglomerated C54 TiSi2 grains was found in some of the 5×5 μm2 contact windows, while only C49 existed in the 0.7×0.7 μm2 windows. Agglomeration is shown to lead to possible C49−C54 coexistence, as well as erroneous interpretation of the C54 nucleation density. Decreasing the As dose to 5×1015 cm−2 leads to a thicker TiSi2 layer, but does not have a major influence on phase formation in the small windows, although only C54 TiSi2 was found in the large ones. In the presence of a thin Nb layer between Ti and poly-Si, C40 (Ti,Nb)Si2 was consistently found in all contacts, indicating that formation does not depend on the contact size at least down to 0.5 μm2. Surprisingly, Ti was found on both sides of the (Ti,Nb)Si2 layer and the silicide near the interface to Si was relatively rich in Ti instead of Nb. © 2003 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Ct Interface structure and roughness
85.40.Ls Metallization, contacts, interconnects; device isolation
68.37.Lp Transmission electron microscopy (TEM)
61.80.Jh Ion radiation effects
64.75.-g Phase equilibria

Preparation and optical characterization of Au/SiO2 composite films with multilayer structure

H. B. Liao, Weijia Wen, and G. K. L. Wong

J. Appl. Phys. 93, 4485 (2003); http://dx.doi.org/10.1063/1.1560569 (4 pages) | Cited 21 times

Online Publication Date: 28 March 2003

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An investigation of Au/SiO2 composite multilayer films with a large third-order optical nonlinearity is reported in this article. Multilayer films containing Au nanoparticles with narrow size and shape distributions can be obtained by controlling the thickness of the Au layer, as well as the annealing temperature and time duration. It is found that the peak of surface plasmon resonance (SPR) of films with mean nanoparticle size of 30 nm is located at 2.35 eV with a width of 350 meV. The SPR peak of films containing larger or smaller particles red-shifts and broadens due to the particle size and shape effects. The third-order optical nonlinear susceptibility χ(3) of these films has a maximum value of about 5.1×10−6 esu at 532 nm when the mean nanoparticle size is around 30 nm. We attribute the observed size dependence of χ(3) to the competition between the enhancement of the local field factor and the skin-depth effect. © 2003 American Institute of Physics.
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42.65.An Optical susceptibility, hyperpolarizability
61.46.-w Structure of nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.22.Lp Collective excitations
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
81.07.Bc Nanocrystalline materials

Surface structural transformation of sintered alumina induced by excimer laser irradiation

C. Dupas-Bruzek, L. D. Laude, F. Langenhorst, and K. Kolev

J. Appl. Phys. 93, 4489 (2003); http://dx.doi.org/10.1063/1.1555703 (8 pages) | Cited 3 times

Online Publication Date: 28 March 2003

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Laser surface processing of ceramics is important for several structural, tribological, optical and electronic applications. However, little is known on the transformation mechanism of alumina under excimer laser irradiation. In this work, a sintered alumina type was typically irradiated at 0.8 J cm−2 and cooled at two drastically different rates. Optical investigations on the irradiated specimens allow to conclude that the amount of transformation products is very much dependant on the cooling rates. Transmission electron microscopy observations show that the transformation product is constituted of an amorphous matrix in which are embedded either (i) copper grains (size up to 1 μm) in slowly cooled samples or (ii) smaller copper or CuAl2O4 spinel grains (size up to 100 nm) in rapidly cooled samples. The cement that is present in the starting material at grain boundaries is found to play an important role on the formation of the new amorphous or crystalline materials. All the copper grains exhibit a 〈120〉 common zone axis perpendicular to the irradiated surface and parallel to the bulk-to-surface thermal gradient, which drives that preferred orientation. These results reveal the details of the phenomenology of the laser-induced material transformation. This latter decomposes into (i) the incipient formation of tiny γ-Al2O3 nuclei, (ii) integration of Cu ions present in the melt into these tiny γ-Al2O3 nuclei that transform into CuAl2O4 spinel, and (iii) further sedimentation of Cu ions onto the resulting spinel grains acting as nucleation centers and finally formation of larger copper-rich grains. The minimum nucleation rate of crystalline grains is estimated to be equal to 1024 cm−3 s−1, while the growth rate is of the order of 0.1 m s−1 in both samples. Both bulk thermal diffusive and convective transports control the transformation of matter. © 2003 American Institute of Physics.
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68.35.Rh Phase transitions and critical phenomena
79.20.Ds Laser-beam impact phenomena
68.35.Fx Diffusion; interface formation
61.82.Ms Insulators
61.72.Mm Grain and twin boundaries
68.37.Lp Transmission electron microscopy (TEM)

Forbidden guided-wave plasmon polaritons in coupled thin films

M. A. Gilmore and B. L. Johnson

J. Appl. Phys. 93, 4497 (2003); http://dx.doi.org/10.1063/1.1558226 (8 pages) | Cited 11 times

Online Publication Date: 28 March 2003

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We study the plasmon-polariton collective modes of a three-thin-film-on-a-substrate structure, where two of the thin films have free-charge carriers and are separated by a static dielectric. We find that this structure can support unusual guided-wave polaritons, which exist in a normally forbidden region of the surface polariton dispersion, and which are composed of coupled surface polariton modes of the individual films with a wavelike transverse electric-field amplitude in the spacer dielectric. The modes emerge from both bulk and surface collective mode bands and evolve into a ladder of solutions in the forbidden region. We also present the attenuated total reflection spectrum arising from the guided modes. © 2003 American Institute of Physics.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Theory of the effects of substitutions on the phase stabilities of Ti1−xAlxN

H. W. Hugosson, H. Högberg, M. Algren, M. Rodmar, and T. I. Selinder

J. Appl. Phys. 93, 4505 (2003); http://dx.doi.org/10.1063/1.1557779 (7 pages) | Cited 39 times

Online Publication Date: 28 March 2003

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We have performed ab initio studies of the effect of substitutions on the phase stabilities of Ti1−xAlxN, x=0−1. The nonmetal substitutions studied include B, C, O, and Si. Metal substitutions studied include Sc, Zr, V, Cr, and Mn. The main objective has been to suggest substitutions that increase the thermal stability of the NaCl structure of Ti1−xAlxN at high Al contents. From these extensive and consistent calculations, some possible avenues for such stabilization present themselves, among which substitution with nonmetal C and Si, and metal V, Cr, and Mn are found to be the most promising. © 2003 American Institute of Physics.
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61.66.Fn Inorganic compounds

Magnetic and structural properties of Co, Cr, V ion-implanted GaN

J. S. Lee, J. D. Lim, Z. G. Khim, Y. D. Park, S. J. Pearton, and S. N. G. Chu

J. Appl. Phys. 93, 4512 (2003); http://dx.doi.org/10.1063/1.1561587 (5 pages) | Cited 51 times

Online Publication Date: 28 March 2003

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We report on the magnetic and structural properties of epitaxial metal organic chemical vapor deposition grown p-GaN:Mg/Al2O3 implanted with Co, Cr, and V ions at varying high doses at 350 °C. Magnetic and structural properties were investigated after a short anneal at 700 °C to remove implantation damage. Magnetic properties determined from superconducting quantum interference device magnetometer measurements indicate ferromagnetic-like ordering for Co and Cr doped samples up to 320 K, while V doped samples show paramagnetic behavior for all temperatures considered. For all samples studied, structural characterization techniques such as x-ray diffraction, high-resolution cross-sectional transmission electron microscopy, and selected area diffraction pattern, indicate no second phases that may contribute to the magnetic properties measured. Transport measurements (resistivity as a function of temperature) reveal all samples to show insulating-like behavior. © 2003 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.20.Ck Nonmetals
61.72.Cc Kinetics of defect formation and annealing
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Electron-beam interactions in Cu–GeSe2 amorphous thin films

J. S. Romero and A. G. Fitzgerald

J. Appl. Phys. 93, 4517 (2003); http://dx.doi.org/10.1063/1.1561994 (4 pages)

Online Publication Date: 28 March 2003

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Copper migration and surface expansion of irradiated areas are observed in amorphous germanium-based chalcogenide thin films when an electron beam is focused in pulsed or continuous operation on the surface of these thin films. Both phenomena can be explained using a simple model in which the population of D− centers is considered to increase upon electron irradiation. The increase in the D− center population is envisaged as due to the breaking of bonds by the electron radiation and by the constant presence of negative charge in irradiated regions. Changes in copper concentration of 20%–30% and surface expansions of 30%–40% of films thickness have been obtained. © 2003 American Institute of Physics.
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79.20.Kz Other electron-impact emission phenomena
66.30.J- Diffusion of impurities
68.55.-a Thin film structure and morphology

Two-dimensional growth of high-quality strontium titanate thin films on Si

H. Li, X. Hu, Y. Wei, Z. Yu, X. Zhang, R. Droopad, A. A. Demkov, J. Edwards, K. Moore, W. Ooms, J. Kulik, and P. Fejes

J. Appl. Phys. 93, 4521 (2003); http://dx.doi.org/10.1063/1.1562001 (5 pages) | Cited 61 times

Online Publication Date: 28 March 2003

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Most semiconductor materials such as Si, Ge, and GaAs are subject to oxidation when exposed to oxidants. This results in difficulties in the heterointegration of epitaxial oxides on these semiconductors. Even though certain oxides may be thermodynamically stable when placed in contact with semiconductors, direct epitaxy of these oxides encounters kinetic difficulties due to the loss of epitaxy caused by the formation of an amorphous oxide at the interface. In this article, we address some important issues on the heteroepitaxy of oxides on semiconductors and show a stepped growth method that utilizes the kinetic characteristics of the growth process to suppress the oxidation of the substrate surface and thereby achieve oxide films with a high degree of crystallinity. The epitaxy of high-quality SrTiO3 (STO) thin films directly on Si was achieved. The chemical and structural properties of the STO/Si interface were evaluated in situ using reflection high-energy electron diffraction, x-ray photoelectron spectroscopy, and scanning tunneling microscopy, and ex situ using transmission electron microscopy and electron energy loss spectroscopy. © 2003 American Institute of Physics.
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68.55.A- Nucleation and growth
68.35.Ct Interface structure and roughness
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.37.Lp Transmission electron microscopy (TEM)
79.20.Uv Electron energy loss spectroscopy
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
79.60.Jv Interfaces; heterostructures; nanostructures

Comparison of arsenic diffusion in Si1−xGex formed by epitaxy and Ge+ implantation

M. J. Mitchell, P. Ashburn, J. M. Bonar, and P. L. F. Hemment

J. Appl. Phys. 93, 4526 (2003); http://dx.doi.org/10.1063/1.1561996 (3 pages) | Cited 4 times

Online Publication Date: 28 March 2003

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A comparison is made of arsenic diffusion in Si0.95Ge0.05 produced by epitaxy and ion beam synthesis using a 2×1016 cm−2 Ge+ implant into silicon. The arsenic diffusion depth at 1025 °C in the Si0.95 Ge0.05 epitaxy sample is enhanced by a factor of 1.26 compared with a similar Si control sample and by a factor of 1.30 in the ion beam synthesized sample. The arsenic diffusion in the Si0.95 Ge0.05 epitaxy sample is modeled by increasing the arsenic diffusion coefficient from the Si value of 1.92×10−15 to 5.15×10−15 cm2 s−1, and in the ion beam synthesized sample by using the same diffusion coefficient of 5.15×10−15 cm2 s−1 and increasing the “plus one” factor in the transient enhanced diffusion model from 0.01 to 1.5. Arsenic diffusion in a silicon sample implanted with 2×1015 cm−2 Si+ can be modeled using the same plus one factor of 1.5, thereby demonstrating the consistency of the modeling. © 2003 American Institute of Physics.
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66.30.J- Diffusion of impurities
61.72.up Other materials
61.72.S- Impurities in crystals
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.82.Fk Semiconductors
61.80.Jh Ion radiation effects

Currents produced by explosive driven transverse shock wave ferromagnetic source of primary power in a coaxial single-turn seeding coil of a magnetocumulative generator

Sergey I. Shkuratov, Evgueni F. Talantsev, James C. Dickens, and Magne Kristiansen

J. Appl. Phys. 93, 4529 (2003); http://dx.doi.org/10.1063/1.1558968 (7 pages) | Cited 7 times

Online Publication Date: 28 March 2003

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Experimental and digital simulation studies of the generation of seed currents by an ultracompact (8.66–8.75 cm3 in volume) ferromagnetic explosive-driven generator of primary power (FMG) loaded on the coaxial single-turn seeding coil of a magnetocumulative generator (MCG) have been performed. The operation of the FMG is based on transverse shock wave demagnetization of Nd2Fe14B high-energy hard ferromagnets. The FMG is capable of producing in the coaxial seeding coil of MCG a seed current with peak amplitude I(t)max=3.0 kA and full width at half maximum of 60 μs. The methodology was developed for digital simulation of the seeding processes in the combined FMG/MCG system. © 2003 American Institute of Physics.
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07.55.Db Generation of magnetic fields; magnets
84.50.+d Electric motors
85.70.-w Magnetic devices
75.50.Ww Permanent magnets
75.50.Bb Fe and its alloys
75.60.-d Domain effects, magnetization curves, and hysteresis
62.50.-p High-pressure effects in solids and liquids
84.30.Ng Oscillators, pulse generators, and function generators
84.32.Hh Inductors and coils; wiring
75.80.+q Magnetomechanical effects, magnetostriction
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