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15 Jun 1995

Volume 77, Issue 12, pp. 6087-6738

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Micromagnetic modeling of magnetic anisotropy in textured thin‐film media

Yang Zhao and H. Neal Bertram

J. Appl. Phys. 77, 6411 (1995); http://dx.doi.org/10.1063/1.359114 (5 pages) | Cited 15 times

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Existing micromagnetic models, based on single domain grains that individually follow coherent rotation during reversal, have been utilized to study the effect of various texture‐induced microstructures on the hysteretic behavior of Co‐alloy thin films with circumferentially textured substrates. The roles of preferential orientation of Co c axes, grain elongation, and segregation, as well as possible short‐range intergranular coupling, have been examined in an effort to understand the origins of widely observed magnetic anisotropy in these media. Preferential c‐axis distribution along the track direction yields reasonable remanences and coercivities for both circumferential and radial loops, but the observed loop closure remains unaccounted for by c‐axis distribution alone. Closely packed arrays of elongated grains maintain relative isotropy in terms of magnetostatic interactions, while voids along texture lines contribute to the magnetostatic anisotropy of the film. The limitations of the model are also discussed. © 1995 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Influence of demagnetization in remanence curves of magnetic thin films

J. G. Th. te Lintelo and J. C. Lodder

J. Appl. Phys. 77, 6416 (1995); http://dx.doi.org/10.1063/1.359115 (10 pages) | Cited 2 times

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Remanent magnetization curves of perpendicular magnetic thin films are simulated and measured. The simulations are used to investigate the theoretical influence of the strong demagnetizing field present in these films. Conclusions are drawn from this on how remanence curves should be measured and how they should be corrected for the demagnetizing influence. The experimental part consists of measurements on Fe‐Alumite, Co‐Pt–based multilayers, and Co‐Cr. In addition the latter material is also artificially patterned into microstrips in order to investigate the influence of demagnetization on remanence curves experimentally. © 1995 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Survey of the dependence on temperature of the coercivity of garnet films

G. Vértesy and I. Tomás

J. Appl. Phys. 77, 6426 (1995); http://dx.doi.org/10.1063/1.359116 (6 pages) | Cited 4 times

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The temperature dependence of the domain‐wall coercive field of epitaxial magnetic garnets films has been investigated in the entire temperature range of the ferrimagnetic phase, and has been found to be described by a set of parametric exponents. In subsequent temperature regions different slopes were observed, with breaking points whose position was found to be sample dependent. A survey based on literature data as well as on a large number of our own samples shows the general existence of this piecewise exponential dependence and the presence of the breaking points. This type of domain‐wall coercive field temperature dependence was found in all samples in the large family of the epitaxial garnets (about 30 specimens of more than ten chemical compositions) and also in another strongly anisotropic material (TbFeCo). © 1995 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Investigation of 90° coupling in Fe/Ag/Fe structures: ‘‘Loose spins’’ and fluctuation mechanism

M. Schäfer, S. Demokritov, S. Müller‐Pfeiffer, R. Schäfer, M. Schneider, P. Grünberg, and W. Zinn

J. Appl. Phys. 77, 6432 (1995); http://dx.doi.org/10.1063/1.359117 (7 pages) | Cited 20 times

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Results are outlined of experimental work concerning Slonczewski’s theories explaining 90° coupling: ‘‘loose spin’’ theory and thickness‐fluctuation mechanism. The loose spin theory suggests that 90° coupling originates from paramagnetic impurities in the interlayer of an exchange‐coupled layered structure. The influence of these paramagnetic impurities on the magnetic exchange coupling was studied using the wedge technique. High‐quality single‐crystalline Fe/Ag/Fe samples were prepared in UHV and each sample consisted of two wedges: one wedge with additional Fe deliberately inserted during growth into the Ag interlayer and one wedge with a pure Fe/Ag/Fe structure. The detailed analysis of magneto‐optic hysteresis loops revealed quantitatively the bilinearly and the 90° coupling strength. As predicted by loose spin theory additional Fe in the Ag spacer lead to a strong temperature dependence of the 90° coupling. According to the theory an increase of 90° coupling strength proportional to impurity concentration was detected while the strength of bilinear coupling decreased. For the pure Fe/Ag/Fe structure, a linear increase of the 90° coupling strength with decreasing temperature was observed. This result can be explained within the fluctuation mechanism which creates 90° coupling through a combination of interface roughness and intralayer ferromagnetic exchange. © 1995 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Conventional and photothermally modulated ferromagnetic resonance investigations of anisotropy fields in an epitaxial Fe(001) film

R. Meckenstock, O. von Geisau, J. Pelzl, and J. A. Wolf

J. Appl. Phys. 77, 6439 (1995); http://dx.doi.org/10.1063/1.359519 (10 pages) | Cited 15 times

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Conventional angle‐dependent ferromagnetic resonance (FMR) measurements on an epitaxial (001) Fe film grown on a GaAs substrate were performed as a function of the orientation of the external magnetic field Bext for three configurations: One with Bext in the film plane and two with Bext out of plane starting in plane in different crystallographic orientations. From these measurements the magnetization M, the crystalline anisotropy constants K1 and K2, the surface anisotropy Ks and an additional uniaxial anisotropy Ku were deduced self‐consistently. The temperature dependence of K1 and M was investigated for the in‐plane [110] orientation in the range from 100 to 570 K. In addition, locally resolved photothermally modulated FMR measurements were carried out to study the homogeneity of the magnetization and of the crystalline anisotropy across the film. Disturbances of both magnetic parameters as a function of position were observed which are related to local inhomogeneities in the semiconducting substrate. © 1995 American Institute of Physics.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys

Mechanical fatigue in thin films induced by piezoelectric strains as a cause of ferroelectric fatigue

K. Khachaturyan

J. Appl. Phys. 77, 6449 (1995); http://dx.doi.org/10.1063/1.359118 (7 pages) | Cited 23 times

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It is proposed that the ferroelectric fatigue is caused by alternating mechanical stresses induced piezoelectrically. It is shown that the mechanical stresses that develop upon switching are sufficient to cause significant mechanical fatigue after the similar number of cycles after which the ferroelectric fatigue is typically observed. It is proposed that the degradation of the ferroelectric properties is a direct consequence of the mechanical fatigue. It is attempted to explain some of the reported correlations between ferroelectric fatigue and microstructure, temperature, test conditions, and electrode material. It is proposed that electromigration and chemomechanical effect are essential in the mechanism of the effect of electrode material on ferroelectric fatigue. © 1995 American Institute of Physics.
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77.65.-j Piezoelectricity and electromechanical effects
68.60.Bs Mechanical and acoustical properties

Dielectric mixture model for a hollow‐ceramic‐sphere composite

Jay G. Liu and David L. Wilcox

J. Appl. Phys. 77, 6456 (1995); http://dx.doi.org/10.1063/1.359119 (5 pages) | Cited 3 times

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A layered sphere Bruggeman effective‐medium model was developed to describe the dielectric constant of a porous ceramic composite having potential for use as a very low dielectric constant inorganic material for microelectronic packaging. The uniqueness of this model is that it incorporates a hollow sphere geometry and thus fits closely the microstructure of the dielectric composite in a broad range of compositions. Samples of the composite were prepared by adding hollow alumina‐silica alloy ceramic spheres to a cordierite matrix. Their dielectric properties were characterized as a function of volume fraction of hollow spheres. The measured results were in good agreement with the model prediction. © 1995 American Institute of Physics.
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77.22.-d Dielectric properties of solids and liquids
77.84.Lf Composite materials
81.05.Pj Glass-based composites, vitroceramics

Ferroelectric properties in epitaxially grown BaxSr1−xTiO3 thin films

Kazuhide Abe and Shuichi Komatsu

J. Appl. Phys. 77, 6461 (1995); http://dx.doi.org/10.1063/1.359120 (5 pages) | Cited 96 times

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Induced ferroelectricity was observed in epitaxially grown BaxSr1−xTiO3 (BST) thin films with thicknesses of about 220 nm. The BST films with various Ba content were deposited at 600 °C on Pt/MgO substrates, by radio frequency magnetron sputtering with double targets, BaTiO3 and SrTiO3. The epitaxial growth of the BST films was confirmed with x‐ray‐diffraction and reflection high‐energy electron‐diffraction analyses. The D–E hysteresis curve and the Curie temperature shift confirmed the BST films with Ba content x≥0.44 had ferroelectricity at room temperature. The mechanism of the ferroelectricity appearance was discussed in relation to the elongation of the c axis in the thickness direction, caused by lattice mismatch between Pt and BST. © 1995 American Institute of Physics.
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77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
68.55.-a Thin film structure and morphology

Growth and ferroelectricity of epitaxial‐like BaTiO3 films on single‐crystal MgO, SrTiO3, and silicon substrates synthesized by pulsed laser deposition

W. J. Lin, T. Y. Tseng, H. B. Lu, S. L. Tu, S. J. Yang, and I. N. Lin

J. Appl. Phys. 77, 6466 (1995); http://dx.doi.org/10.1063/1.359121 (6 pages) | Cited 23 times

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The epitaxial‐like BaTiO3 (BTO) films with good ferroelectricity are obtained both on (001)SrTiO3 (STO) single crystal and on CeO2 buffered silicon substrate by pulsed laser deposition. The deposition parameters need to be stringently controlled in order to grow BTO films with good crystallinity. The BTO films grown on YBa2Cu3O7−x (YBCO)/CeO2/STO substrates are epitaxial, as confirmed by rocking curve, ϕ scan, and wide‐angle x‐ray‐diffraction techniques. The alignment of a and b axes of BTO films on YBCO/CeO2/Si substrate is, however, not as perfect as BTO film on YBCO/STO substrate. The BTO/YBCO/CeO2/Si films are only (00l) textured. The ferroelectric property measurement, using the YBCO layer as the base electrode material, shows that the remanent polarization Pr and coercive field Ec of the BTO/YBCO/CeO2/Si films (Pr=3.6 μC/cm2, Ec=11.1 kV/cm) are, however, as good as those of the BTO/YBCO/STO films (Pr=4.0 μC/cm2, Ec=12.5 kV/cm). © 1995 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
81.15.Fg Pulsed laser ablation deposition

Analysis of Franz–Keldysh oscillations in photoreflectance spectra of a AlGaAs/GaAs single‐quantum well structure

P. J. Hughes, B. L. Weiss, and T. J. C. Hosea

J. Appl. Phys. 77, 6472 (1995); http://dx.doi.org/10.1063/1.359122 (9 pages) | Cited 30 times

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Experimental results are presented for the physical origins of room‐temperature photoreflectance features of a AlGaAs/GaAs single‐quantum well structure. The spectra exhibit well‐defined Franz–Keldysh oscillations which overlap with photoreflectance features due to the quantum well and complicate the determination of the energies of the transitions within the quantum well. The origin of the Franz–Keldysh oscillations are determined using wet chemical etching to selectively remove grown layers down to the substrate. The resulting spectra are presented as a function of etch depth which allows the magnitude of the built‐in electric fields to be determined and reveals the location within the quantum well structure where the Franz–Keldysh oscillations originate. © 1995 American Institute of Physics.
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78.66.Fd III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Process‐induced strains in dry etched semiconductor nanostructures studied by photoreflectance

Y. S. Tang, P. D. Wang, C. M. Sotomayor Torres, B. Lunn, and D. E. Ashenford

J. Appl. Phys. 77, 6481 (1995); http://dx.doi.org/10.1063/1.359123 (4 pages) | Cited 5 times

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This article reports a photoreflectance study of the process‐induced strains in both dry etched CdTe/Cd0.875Mn0.125Te and GaAs/Al0.3Ga0.7As nanostructures patterned by electron beam lithography. The results show that compressive strains can be introduced in both the dry etched nanostructures and the layers underneath the etched surfaces due to the introduction of defect complexes and/or crystographic damage inflicted in the fabrication process. The effect of post dry etch thermal annealing on the strains in the dry etched nanostructures has also been studied. © 1995 American Institute of Physics.
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78.66.Fd III-V semiconductors
68.60.Bs Mechanical and acoustical properties
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.40.Hp Lithography, masks and pattern transfer

Optimization and analysis of solar selective surfaces with continuous and multilayer profiles

Y. Yin and R. E. Collins

J. Appl. Phys. 77, 6485 (1995); http://dx.doi.org/10.1063/1.359124 (7 pages) | Cited 7 times

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Both continuous and multilayer profiles of solar selective surfaces have been analyzed and optimized. The structure having the highest photothermal efficiency has two uniform absorbing layers with two antireflection layers of different refractive index materials. Interference effects were analyzed in terms of optical path length of the sublayers and their combination. The phase cancellation positions for the optimized multilayer profiles are well distributed in the solar radiation range but do not occur at wavelengths above about 2.5 μm. A study of the electric‐field distribution in these optimized profiles has shown that the sharp transition at above about 2.5 μm from low to high reflectance is due to the absence of high filling factor sublayers which can act as an effective reflecting substrate. The selective properties of the optimized multilayer structures are not particularly sensitive to the optimized graded profile for thickness variations of ±20%. © 1995 American Institute of Physics.
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78.66.-w Optical properties of specific thin films
42.79.Ek Solar collectors and concentrators
42.25.Bs Wave propagation, transmission and absorption

Electron relaxation time measurements in GaAs/AlGaAs quantum wells: Intersubband absorption saturation by a free‐electron laser

J. Y. Duboz, E. Costard, E. Rosencher, P. Bois, J. Nagle, J. M. Berset, D. Jaroszynski, and J. M. Ortega

J. Appl. Phys. 77, 6492 (1995); http://dx.doi.org/10.1063/1.359125 (4 pages) | Cited 9 times

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The intersubband absorption saturation in GaAs/AlGaAs quantum wells as a function of the incident power has been measured, using picosecond micropulses with a power density up to 1 GW/cm2 delivered by a free‐electron laser. The absorption in a sample with a bound‐to‐bound transition was compared to the absorption in a sample with a bound‐to‐resonant transition, and it was found that the electron relaxation time in the bound‐to‐bound transition is about four times shorter than for the bound‐to‐resonant transition. © 1995 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Interference oscillations in Fourier‐transform infrared spectra of AlSb/GaSb superlattices

Guoping Ru, Yanlan Zheng, and Aizhen Li

J. Appl. Phys. 77, 6496 (1995); http://dx.doi.org/10.1063/1.359126 (4 pages) | Cited 1 time

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The interference oscillations in normal‐incident Fourier‐transform infrared (FTIR) spectra of AlSb/GaSb superlattices, which disturb the observation of intersub‐band transitions, have been theoretically simulated and experimentally measured. Both theoretical and experimental results show that on GaSb substrates, interference oscillations are relatively weak when using GaSb rather than AlSb as the buffer layer; and by contrast, on GaAs substrates, they are weak when using AlSb rather than GaSb as the buffer layer. Using an AlSb buffer on semi‐insulating GaAs substrates, normal‐incident intersub‐band transitions from L1 to L2 sub‐bands in AlSb/GaSb superlattices have been observed by the usual FTIR technique. © 1995 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Study on symmetry forbidden transitions in an InxGa1−xAs/GaAs single quantum well by temperature dependence

D. P. Wang, C. T. Chen, H. Kuan, S. C. Shei, and Y. K. Su

J. Appl. Phys. 77, 6500 (1995); http://dx.doi.org/10.1063/1.359058 (4 pages) | Cited 2 times

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The photoreflectance (PR) spectroscopy of the single quantum well InxGa1−xAs/GaAs system has been measured at various temperatures. The selection rules for the interband transitions are Δn=0, where n is the quantum number of the nth subband in the quantum well. The symmetry forbidden transitions (Δn≠0), such as 12H (where mnH denotes transition between the mth conduction to nth valence subband of heavy hole), were often observed in the experiments and it was attributed to the existence of the built‐in electric field in the quantum well. In this work, we change the strength of the built‐in electric field by varying the temperatures of the samples. By varying the temperatures of the samples, the strength of the field can be changed by the effect of photo‐induced voltages. The measured ratios of the intensities of 12H to 11H transitions decrease as the temperatures are lowered. Therefore, the existence of the built‐in electric field may account for the observations of the symmetry forbidden transition 12H in the experiments. © 1995 American Institute of Physics.
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78.66.Fd III-V semiconductors

Erbium in oxygen‐doped silicon: Electroluminescence

S. Lombardo, S. U. Campisano, G. N. van den Hoven, and A. Polman

J. Appl. Phys. 77, 6504 (1995); http://dx.doi.org/10.1063/1.359059 (7 pages) | Cited 40 times

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Room‐temperature electroluminescence at 1.54 μm is demonstrated in erbium‐implanted oxygen‐doped silicon (27 at. % O), due to intra‐4f transitions of the Er3+. The luminescence is electrically stimulated by biasing metal‐(Si:O, Er)‐p+ silicon diodes. The 30‐nm‐thick Si:O, Er films are amorphous layers deposited onto silicon substrates by chemical‐vapor deposition of SiH4 and N2O, doped by ion implantation with Er to a concentration up to ≊1.5 at. %, and annealed in a rapid thermal annealing furnace. The most intense electroluminescence is obtained in samples annealed at 400 °C in reverse bias under breakdown conditions and it is attributed to impact excitation of erbium by hot carriers injected from the Si into the Si:O, Er layer. The electrical characteristics of the diode are studied in detail and related to the electroluminescence characteristics. A lower limit for the impact excitation cross section of ≊6×10−16 cm2 is obtained. © 1995 American Institute of Physics.
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78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
61.72.uf Ge and Si

Trapping of photocarriers in Ga‐doped Bi12GeO20 at 80 K

D. Bloom and S. W. S. McKeever

J. Appl. Phys. 77, 6511 (1995); http://dx.doi.org/10.1063/1.359060 (10 pages) | Cited 14 times

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Data from measurements of optical absorption, photoconductivity, dark conductivity, thermally stimulated conductivity (TSC), and thermoluminescence (TL) on samples of undoped and Ga‐doped, Czochralski‐grown Bi12GeO20 single crystals are reported. The photoconductivity is n type, and the dark conductivity is p type. Undoped BGO exhibits a broad, band‐edge absorption due to the optical excitation of electrons to the conduction band which gives the samples a yellow coloration. This absorption is reduced by the addition of Ga which acts as a compensating acceptor. When illuminated with light into this absorption band, but with photons of energy less than the band gap, photoexcitation of electrons occurs. These become trapped, inducing additional absorption and photoconductivity bands and TSC signals, but not TL. Excitation with photons of energy greater than the band gap induces both TSC and TL. Examination of the TSC and TL signals as a function of excitation wavelength allows the distinction between electron and hole trapping states for which trapping parameters have been determined. In addition, dark conductivity reveals three major hole states at energies of ∼Ev+1.41, ∼Ev+0.86, and ∼Ev+0.54 eV. These are believed to be empty donor states. © 1995 American Institute of Physics.  
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72.40.+w Photoconduction and photovoltaic effects
78.60.Kn Thermoluminescence

Trap level spectroscopy of undoped and Ga‐doped Bi12GeO20 using thermally stimulated conductivity

D. Bloom and S. W. S. McKeever

J. Appl. Phys. 77, 6521 (1995); http://dx.doi.org/10.1063/1.359061 (13 pages) | Cited 9 times

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The analysis of thermally stimulated conductivity (TSC) measurements performed on ‘‘pure’’ Bi12GeO20 (BGO) and BGO doped with gallium is presented. The TSC data show many overlapping TSC peaks in the temperature range of interest (80–300 K) which arise from a complex array of trapping states. The TSC signals from both pure BGO and Ga‐doped BGO are similar, consisting of a series of large peaks below 160 K and many smaller overlapping peaks between 180 and 300 K. The analysis shows that the large peaks below 160 K in undoped BGO arise from two trapping centers, each characterized by a distribution of activation energies centered at ∼0.24 and ∼0.29 eV, with distribution widths of ∼0.065 eV. In the Ga‐doped BGO sample the large peak seen below 180 K arises from a single trapping center at ∼0.29 eV with a distribution width of ∼0.085 eV. Activation energies, frequency factors, and concentrations of trapping states have been determined. © 1995 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
71.55.Ht Other nonmetals

Optical properties of silicon nitride films deposited by hot filament chemical vapor deposition

Sadanand V. Deshpande, Erdogan Gulari, Steven W. Brown, and Stephen C. Rand

J. Appl. Phys. 77, 6534 (1995); http://dx.doi.org/10.1063/1.359062 (8 pages) | Cited 91 times

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Silicon nitride films were deposited at low temperatures (245–370 °C) and high deposition rates (500–1700 Å/min) by hot filament assisted chemical vapor deposition (HFCVD). Optical properties of these amorphous silicon nitride thin films have been extensively characterized by absorption, photoluminescence (PL), photoluminescence excitation, and electroluminescence measurements. The optical band gap of the films was varied between 2.43 and 4.74 eV by adjusting the flow rate of the disilane source gas. Three broad peaks at 1.8, 2.4, and 3.0 eV were observed in the PL spectra from these films. A simple qualitative model based on nitrogen and silicon dangling bonds adequately explains the observed PL features. The photoluminescence intensity observed in these films was 8–10 times stronger than films deposited by plasma enhanced chemical vapor deposition, under similar conditions. The high deposition rates obtained by HFCVD is believed to introduce a large number of these optically active defects. © 1995 American Institute of Physics.
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78.66.Nk Insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.55.Hx Other solid inorganic materials
78.60.Fi Electroluminescence

Microstructures of low‐temperature‐deposited polycrystalline silicon with micrometer grains

K. C. Wang, H. L. Hwang, P. T. Leong, and T. R. Yew

J. Appl. Phys. 77, 6542 (1995); http://dx.doi.org/10.1063/1.359063 (7 pages) | Cited 12 times

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The microstructures of low‐temperature polycrystalline silicon grown both on SiO2 and Corning 7059 glass substrate are presented. The silicon was deposited by the hydrogen dilution method using electron‐cyclotron‐resonance chemical‐vapor deposition at 250 °C without any thermal annealing. The hydrogen dilution ratios were varied from 90% to 99%. Transmission electron microscopy images, Raman shift spectra, and x‐ray‐diffraction (XRD) patterns of the films were obtained. The maximum grain size was about 1 μm and the crystalline fraction which was characterized from Raman shift spectra was near 100%. From the XRD patterns 〈111〉‐ and 〈110〉‐oriented crystalline silicon grains were clearly present in the polycrystalline silicon films. © 1995 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Effects of biaxial strain on the intervalence‐band absorption spectra of InGaAs/InP systems

A. Afzali‐Kushaa and G. I. Haddad

J. Appl. Phys. 77, 6549 (1995); http://dx.doi.org/10.1063/1.359064 (8 pages) | Cited 4 times

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The effects of biaxial strain on the intervalence‐band absorption spectra of p‐doped InGaAs/InP bulk layers are investigated. The study is performed by calculating and comparing the absorption coefficients corresponding to the direct transitions between the heavy and light hole bands, between the heavy hole and split‐off bands, and between the split‐off and light hole bands in both the lattice matched and the strained layers. The valence‐band structures of these layers are neither isotropic nor parabolic and hence the k⋅p approach is utilized to calculate the band structures and their corresponding wave functions. The quantities are then invoked in the calculation of the (joint) density of states, the Fermi energy, and the momentum matrix element, which are needed in the evaluation of the intervalence‐band absorption coefficients. These calculated results show that the intervalence‐band absorption coefficients depend on the strain in the layer. The dependence is determined by the bands involved in the intervalence transition, the polarization of the incident light, and the type of the strain (compressive or tensile). © 1995 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Influence of defects on electron–hole plasma recombination and transport in a nipi‐doped InxGa1−xAs/GaAs multiple‐quantum well structure

D. H. Rich, H. T. Lin, and A. Larsson

J. Appl. Phys. 77, 6557 (1995); http://dx.doi.org/10.1063/1.359065 (12 pages) | Cited 9 times

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The nonlinear optical and transport properties of a nipi‐doped InxGa1−xAs/GaAs multiple‐quantum well sample (x=0.23) has been studied using a novel approach called electron‐beam‐induced absorption modulation (EBIA). The absorption in the sample is modulated as a result of screening of the built‐in electric field in the nipi structure due to excess carrier generation. The change in field causes a Stark shift of the first quantized optical transitions in QWs which are situated in the intrinsic layers. In EBIA, a scanning electron probe is used to locally generate an electron–hole plasma that is used to study the spatial distribution of defects that impede excess carrier transport and reduce the lifetime of spatially separated carriers. The Stark shift in the MQW structure is imaged with micrometer‐scale resolution and is compared with cathodoluminescence imaging results which show dark line defects resulting from strain‐induced misfit dislocations. Theoretical calculations using Airy functions in the transfer‐matrix method with a self‐consistent field approximation were used to determine the energy states, wave functions, and carrier recombination lifetimes of the MQW as a function of the built‐in field. A quantitative phenomenological analysis is employed to determine the built‐in field, excess carrier lifetime, and ambipolar diffusion coefficient as a function of the excitation density. The defects are found to create potential barriers and recombination centers which impede transport and markedly reduce the excess carrier lifetime. © 1995 American Institute of Physics.  
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78.66.Fd III-V semiconductors
78.20.Jq Electro-optical effects
71.55.Eq III-V semiconductors

Acoustical and optical properties of Ga0.52In0.48P: A Brillouin scattering study

A. Hassine, J. Sapriel, P. Le Berre, P. Legay, F. Alexandre, and G. Post

J. Appl. Phys. 77, 6569 (1995); http://dx.doi.org/10.1063/1.359066 (3 pages) | Cited 2 times

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Brillouin scattering is used to determine the refractive index N=n+iκ of Ga0.52In0.48P layers, lattice matched to GaAs, in a wavelength range never investigated before (400 nm<λ<800 nm). It is shown that the variations of n are given by two different analytical expressions, depending on whether the corresponding photon energies E are lower or higher than the band gap Eg. Optical absorption measurements are deduced from the Brillouin linewidth. The whole set of elastic constant is also determined through the Brillouin shifts. For E∼Eg, i.e., in resonance conditions, n displays a small but sharp peak closely related to the abrupt increase of the optical absorption. Besides the Brillouin investigations, complementary results obtained by ellipsometry and Raman spectroscopy confirm our optical properties measurements in Ga0.52In0.48P and the electronic resonance behavior, respectively. © 1995 American Institute of Physics.
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78.66.Fd III-V semiconductors
68.60.Bs Mechanical and acoustical properties
78.35.+c Brillouin and Rayleigh scattering; other light scattering

A quantitative investigation of emission from low temperature laser‐induced YBa2Cu3Ox plasma plumes

A. H. El‐Astal, S. Ikram, T. Morrow, W. G. Graham, and D. G. Walmsley

J. Appl. Phys. 77, 6572 (1995); http://dx.doi.org/10.1063/1.359529 (9 pages) | Cited 21 times

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Quantitative emission spectroscopy has been used to study the plume formed following laser ablation of YBCO in an oxygen atmosphere. Excited state population distributions, determined from emission line intensity ratios, are used to investigate spatiotemporal variations in the local Boltzmann temperatures for both neutral and ionic species within the expanding plume. Temperatures, obtained from emission line intensity ratios of both Cu(I) and Y(I), decrease slowly and nonadiabatically in the range 1.0–0.5 eV during plume expansion. Higher initial Boltzmann temperatures of ∼3 eV are however obtained from the emission line intensity ratios of fast ions, which dominate the composition of the highly luminous expanding front of the plume. Quantitative comparison of emission intensities for the different neutral species present indicate that the neutral composition in the luminous region of the expanding plume is increasingly dominated by Cu(I) which has a faster expansion velocity and lower oxidation rate than Y(I) and Ba(I). © 1995 American Institute of Physics.
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79.20.Ds Laser-beam impact phenomena
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
74.78.-w Superconducting films and low-dimensional structures

Laser photochemical ablation of CdWO4 studied with the time‐of‐flight mass spectrometric technique

Katsumi Tanaka, Takaaki Miyajima, Natsuki Shirai, Quan Zhuang, and Ryohei Nakata

J. Appl. Phys. 77, 6581 (1995); http://dx.doi.org/10.1063/1.359067 (7 pages) | Cited 38 times

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Pulsed laser ablation of CdWO4 at 266 nm is studied with a quadrupole mass spectrometric (QMS) time‐of‐flight method. Ablation threshold, energy distribution, and angular distribution of the ablated species as well as nonlinearity of the ablated species mass intensity are elucidated as a function of laser fluence. Ablated species of O+2, Cd+, Cd2+, W+, and WO+ translate with energies strongly depending on the fragment mass, meaning that they are confined in a space with the same velocity distribution. Ablated species detected with the QMS filament off show a Gaussian distribution for their translation energy, which is interpreted by the Franck–Condon electron excitation mechanism. A simple model is proposed based on a photochemical bond breaking to explain the observed threshold and nonlinearity of the ablated species. Nonlinearity can be explained by photofragmentation of CdWO4 cluster ions and the successively occurring volume expansion. The latter will be the main cause for the desorption of ion species by ablation and supports the narrow angular spreading of the ablated species. © 1995 American Institute of Physics.
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79.20.Ds Laser-beam impact phenomena
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
81.15.Fg Pulsed laser ablation deposition
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