bluuebunny/crossref_metadata_2025 huggingface dataset:
Carrier-Concentration-Dependent Magnetic Properties of the Diluted Magnetic Semiconductor SnMnte
Authors: Swagten H. J. M. , Eltink S. J. E. A. , De Jonge W. J. M.
Published: September 2012

In this paper experimental evidence is presented for the carrier concentration dependence of the magnetic properties of Sn0.97Mn0.03Te, yielding a critical concentration above which ferromagnetic interactions are dominant. The observed behavior can be fairly well explained within a modified RKKY-model. Preliminary experiments on the low temperature magnetic phases indicate re-entrant spinglass behavior, which is qualitatively described with the spinglass model of Sherrington and Kirkpatrick.
In-Situ Techniques for Studying Epitaxially Grown Layers and Determining their Magnetic Properties
Authors: Heinrich B. , Arrott A. S. , Cochran J. F. , Urquhart K. B. , Myrtle K. , Celinski Z. , Zhong Q. M.
Published: September 2012

Ultrathin films of bcc Fe (001) on Ag (001) and Fe/Ni (001) bilayers on Ag were grown by molecular beam epitaxy. A wide range of surface science tools (RHEED, REELFS, AES, and XPS) were employed to establish the quality of epitaxial growth. Ferromagnetic resonance and Brillouin light scattering were used to extract the magnetic properties. Emphasis was placed on the study of magnetic anisotropies. Large uniaxial anisotropies with the easy axis perpendicular to the film surface were observed in all ultrathin structures studied. In sufficiently thin samples the saturation magnetization was oriented perpendicular to the film surface in the absence of an applied field. It has been demonstrated that in bcc Fe films the uniaxial perpendicular anisotropy originates at the film interfaces. Fe/Ni bilayers were also investigated. Ni grows in the pure bcc structure for the first 3–6ML and then transforms to a new structure which exhibits unique magnetic properties. Transformed ultrathin bilayers possesses large in-plane 4th order anisotropies far surpassing those observed in bulk Fe and Ni. The large 4th order anisotropies originate in crystallographic defects formed during the Ni lattice transformation.
Characterization of Epitaxial Fe on GaAs(110) by Scanning Tunneling Microscopy
Authors: Dragoset R. A. , First P. N. , Stroscio Joseph A. , Pierce D. T. , Celotta R. J.
Published: September 2012

Iron on GaAs(110) comprises an interesting system not only due to small lattice mismatch, 1.4%, but also because of the magnetic properties of the overlayer. In the present work, scanning tunneling microscopy (STM) was used to investigate bcc Fe films in the 0.1 Å to 20 Å thickness range, grown at 300 K and 450 K substrate temperatures. STM images show Volmer-Weber growth with the formation of 3-D Fe islands 20–30 Å in diameter for 0.1–1 Å deposition at 300 K, increasing to 40–50 Å for thicker films. Iron island sizes at low coverage and thin film roughness at higher coverages both show significant dependence upon growth temperature.
In-Situ investigation of Structure and Magnetic Properties of the Epitaxial System Pd(111)/Fe(110) on W(110) by Means of Brillouin Spectroscopy
Authors: Baumgart P. , Hillebrands B. , Harzer J. V. , Güntherodt G.
Published: September 2012

The in-situ observation of magnetostatic spin waves by Brillouin spectroscopy offers a versatile dynamical probe for the investigation of magnetic properties of thin films. The measured spin wave spectra of thin films contain a variety of information about their magnetic as well as structural properties. The frequency of a spin wave allows to determine, e.g., the g-factor, the magnetic anisotropy constants and also the saturation magnetization. The spectral line shape allows conclusions about the film quality, i.e., steps or islands. Furthermore, the unidirectional propagation of the surface spin wave with respect to the magnetization allows to measure the coercitivity field of a film. The latter can be used as an additional characterization parameter of a magnetic film.
Structural and Magnetic Characterization of Rare Earth and Transition Metal Films Grown on Epitaxial Buffer Films on Semiconductor
Authors: Farrow R. F. C. , Parkin S. S. P. , Speriosu V. S. , Bezinge A. , Segmuller A. P.
Published: September 2012

Structural and magnetic data are presented and discussed for epitaxial films of rare earth metals ( Dy, Ho, Er) on LaF3 films on the GaAs(TTT) surface and Fe on Ag films on the GaAs(001) surface. Both systems exhibit unusual structural characteristics which influence the magnetic properties of the metal films. In the case of rare earth epitaxy on LaF3 we present evidence for epitaxy across an incommensurate or discommensurate interface. Coherency strain is not transmitted into the metal which behaves much like bulk crystals of the rare earths. In the case of Fe films , tilted epitaxy and long-range coherency strain are confirmed by X-ray diffractometry. Methods of controlling some of these structural effects by modifying the epitaxial structures are presented.
Magnetic Domains in Epitaxial (100) Fe Thin Films
Authors: Florczak Jeffrey M. , Ryan P. J. , Kuznia J. N. , Wowchak A. M. , Cohen P. I. , White R. M. , Prinz G. A. , Dahlberg E. Dan
Published: September 2012

By use of Kerr microscopy, the domain patterns of thin Fe films (10 nm) grown on Inx Ga1-x As (0.09 ≤ x ≤ 0.25)/GaAs substrates have been investigated. For This nvestigation, two types of InGaAs buffer layers were prepared. One consisted of a single, thick InGaAs layer and the second composed of an InGaAs strained layer superlattice. Both were grown on (100) GaAs substrates. The study showed that many of the domain walls were approximately parallel to the easy axis of Fe for those films grown on the low x alloy, e.g. x-0.1, InGaAs buffer layers. In the alloy films with larger values of x, e.g. x-0.2, the domain pattern of the Fe overlayer was strongly influenced by dislocations of the strain relieved InGaAs buffer layer. These dislocations manifested themselves as corrugations parallel to the <110> directions in the InGaAs. Kerr microscopy of a x-0.2 film indicated the presence of long, narrow domains with their long axes parallel to the striations. Although shape anisotropy arguments predicted that the magnetization should be parallel to the striations, magnetometer data indicated that a substantial component of magnetization was oriented perpendicular to the corrugations at low fields. The Fe film grown on the superlattice had magnetic domains very similar to a thick Fe film (0.5 μm) grown on GaAs.
X-Ray Scattering Studies of Thin Films and Multilayers
Authors: Cargill G. S.
Published: September 2012

X-ray scattering experiments provide important information about the atomic scale structure and the microstructure of thin films and multilayers. The high intensity, brightness, and broad energy spectrum of synchrotron radiation greatly extend capabilities of scattering experiments, particularly for scattering from ultrathin films and for anomalous dispersion scattering from alloys. Examples of scattering studies of both crystalline and amorphous materials are given in this overview.
Ferromagnetic and Nuclear Magnetic Resonance Study of Co/Pd Multilayers
Authors: Gronckel H. A. M. De , Swuste C. H. W. , Kopinga K. , Jonge W. J. M. De
Published: September 2012

The microscopic properties of Co/Pd multilayers were studied by ferromagnetic and nuclear magnetic resonance. In addition to previous results the magnetic anisotropy is found to be also a function of the Pd layer thickness, increasing below 20 Å for decreasing thickness. This is ascribed to a decrease in the Pd/Co interface contribution to the anisotropy.

Hyperfine field spectra show a shift to lower hyperfine fields upon decreasing Co sublayer thickness. This is attributed to an expansion of the Co ‘lattice’. Comparison of the results on the [111] multilayers with those on almost single phased [100] multilayers suggests that this expansion is nearly isotropic.
Exafs Study of the Stability of Amorphous TbFe Thin Films
Authors: Samant Mahesh G. , Marinero Ernesto E. , Robinson Clifford , Cargill G. S.
Published: September 2012

EXAFS is used to measure the local atomic structure of Fe in Au doped Tb-Fe thin film alloys. The as deposited sample shows structural fcatures which are essentially identical to those of the undoped films. Au additions stabilizes the amorphous structure against recrystallization, however, the loss of magnetic anisotropy under thermal annealing is not reduced. This demonstrates that magnetic relaxation in these alloys does not involve crystallization of the amorphous structure.
Hrem Structural Studies of TbFeCo Thin Films
Authors: Li Z. G. , Smith David J. , Sickafus K.
Published: September 2012

The microstructure of TbFeCo thin films prepared under different deposition conditions has been observed in crosssection and top-view using high-resolution electron microscopy, as well as conventional bright-field and dark-field techniques. A comparison has been made with FeCo thin films prepared under identical experimental conditions. Very fine microcrystals (sizes 2–5nm) were observed in the basically amorphous TbFeCo thin films whereas much larger crystals (sizes 20–50nm) were visible in the primarily crystalline FeCo thin films. It was also found that the size of the nanocrystals in the TbFeCo films depended upon the argon partial pressure during deposition.
Time-Dependent Landau-Ginzburg Modelling of Magnetic Inhomogeneities and Spiral Domain Structures in Thin Films
Authors: Tuszyński J. A.
Published: September 2012

A Landau-Ginzburg model for a uniaxial ferromagnetic thin film is presented which includes inhomogeneities due to nearest neighbor exchange interactions. The role of external magnetic fields is studied in the determination of exact symmetries of the equation of state. Spiral domain structures allowed by symmetry considerations as exact solutions at the critical and tricritical points have recently been found experimentally in epitaxially grown single-crystal garnet ferrite films. These experiments are discussed from the point of view of our model.
Exchange Anisotropy in Amorphous/Microcrystalline Co-Gd Films
Authors: Toxen A. M. , Hopkins A. , Hagstrom S. B. , White R. M.
Published: September 2012

Magnetization, TEM, and x-ray diffraction studies have been carried out on GdCox films sputtered onto Si or sapphire substrates at ˜90 C, ambient temperature. The composition range studied was x=2−8.5. Over the composition range defined approximately by 5>×>3, the films, which are 1–3 microns thick, exhibit a unidirectionally displaced B-H loop, characteristic of an exchange-biased phase. TEM studies indicated that the samples with the shifted loops indeed consist of a mixture of amorphous and microcrystalline phases. The characteristic size of the microstructure is 10–20 A. Electron diffraction shows a very broad ring characteristic of amorphous phase together with six or seven sharper rings characteristic of crystalline material which index best to the hexagonal GdCo5 structure or to a high temperature hexagonal Gd2Co17 phase. The diffraction pattern remains virtually unchanged over the composition range x=2–8. This leads us to conclude that the microcrystalline material consists of one, or perhaps more than one, metastable phase over the indicated composition range. X-ray diffraction shows only one broad maximum.
X-Ray Diffraction Study of Rare Earth Epitaxial Structures Grown by MBE onto (111) GaAs
Authors: Bennett W. R. , Farrow R. F. C. , Parkin S. S. P. , Marinero E. E.
Published: September 2012

We report on the new epitaxial system LaF3/Er/Dy/Er/LaF3/GaAs (111) grown by molecular beam epitaxy. X-ray diffraction studies have been used to determine the epitaxial relationships between the rare earths, the LaF3 and the substrate. Further studies of symmetric and asymmetric reflections yielded the in-plane and perpendicular strain components of the rare earth layers. Such systems may be used to probe the effects of magnetoelastic interactions and dimensionality on magnetic ordering in rare earth metal films and multilayers.
Magnetic and Crystallographic Interactions of Alternately Deposited Fe and Al ultra-thin Layers
Authors: Nagakubo M. , Yamamoto T. , Naoe M.
Published: September 2012

Multilayered films consisting of ferromagnetic Fe and nonmagnetic Al layers were prepared by using ion beam sputtering, and the relationships between their crystallographic characteristics and soft magnetic properties have been investigated in detail.

The periodicity of the multilayered films was confirmed for various layer thicknesses (ΔFe and ΔA1) above 10Å from their X-ray diffraction peaks at low angle. When ΔFe decreased along with ΔA1 from 100Å, the coercivity Hc decreased and showed a minimum of 1.5 Oe at layer thicknesses of 20Å, but at the same time, the saturation magnetization 4πMs which was estimated from total thickness of the Fe layers decreased from 20 kG and showed drastic decrease at ΔFe below 10Å. For ΔFe above 100Å, 4πMs was constant around 20 kG without dependence on ΔA1. When ΔAl was changed for AFe of 100Å, the values of Hc had a interesting relationship with the crystallite orientation in Fe layers. Namely, the preferentially oriented planes of α-Fe crystallites changed from (110) to (200) in the case of Al layer thinner than 15Å and Hc showed a minimum below 4 Oe for ΔAl in this transition range of crystallite orientation, while 4πMs of all Fe layers themselves was kept at 20 kG. Taking into consideration that the nearest atomic distance of fcc Al and the lattice constant of bcc Fe is almost the same, these results may be caused by crystallographical interaction at the interfaces between Fe and Al layers.
Calculation of Magnetization Processes in Multilayers with Antiferromagnetic Coupling between Adjacent Layers
Authors: Dieny B. , Gavigan J. P. , Rebouillat J. P.
Published: September 2012

This paper presents calculations of hysteresis loops in ferromagnetic multilayer systems of cubic or uniaxial anisotropy with antiferromagnetic coupling between adjacent layers. The case of a bilayer has been systematically studied as a function of the strenght of the anisotropy. The two limiting cases corresponding to either a coherent rotation of the magnetization or to a non-dissipative nucleation-propagation mechanism are investigated. The influence of the number of layers is also discussed.
Giant Magnetoresistance of (001) Fe / (001) Cr Superlattices
Authors: Barthelemy A. , Baibich M. N. , Broto J. M. , Cabanel R. , Creuzet G. , Etienne P. , Fert A. , Friederich A. , Lequien S. , Dau F. Nguyen Van , Ounadjela K.
Published: September 2012

We recently reported the observation of a very large magnetoresistance in (001)Fe/(001)Cr superlattices grown by MBE. The magnetoresistance is found to be very large for thin Cr layers. We ascribe this magnetoresistance to a magnetic gate effect.

We recently reported the observation of a very large magnetoresistance in (001)Fe/(001)Cr superlattices with thin Cr layers [1]. A large magnetoresitance has also been observed in Fe/Cr/Fe sandwhiches [2]. In both cases, for Cr layers thinner than about 30 Å an antiparallel coupling of the magnetization of neighbor Fe layers is indicated by magnetic, magneto-optic and light scattering measurements [1–3]. It thus turns out that the large magnetoresistance os associated with the change to parallel alignment in an applied field. In this paper, we present new data on the magnetic and transport properties of Fe/Cr superlattics and we concentrate on the discussion of the microscopic origin of the magnetoresistance
Spin Polarized Inverse Photoemission Study of Fe and Co Thin Films on W(001)
Authors: Cai Qing , Avci Recep , Lapeyre Gerald J.
Published: September 2012

Spin- (and angle-) resolved inverse photoemission spectroscopy (SPIPES) has beenused for studying magnetic thin films. The spin dependence of the unoccupiedelectronic structure has been investigated for in-situ-grown epitaxial, ultrathin Fe and Cofilms on W(001). The Fe overlayers have a square lattice and exhibit in-plane magneticremanence in the direction of the surface Brilluoin zone. Four or more atomic layersof Fe show bulklike SPIPES spectra with a majority spin peak at the Fermi energy (EF)and a broad minority peak 1.3 eV above EF The Co overlayers on W(001) showdistorted hexagonal structures in the plane with an atomic density twice that of theW(001) plane. Two atomic layers of Co show strong in-plane magnetic remanence withthe minority peak at 0.7 eV. The SPIPES results in general are consistent with thetheoretical electronic structure for momentum-conserving radiative transition from freeelectron-like bands down to the unoccupied 3d bands.
Magnetometry in Ultrathin Films using Spin Polarized Cascade Electrons
Authors: Kay Eric
Published: September 2012

In this review, we show how spin polarized cascade electron spectroscopy provides a relatively rapid and flexible approach to the study of a variety of problems of current interest in both ultrathin magnetic films and surface magnetism. Specific examples relating to the non-bulk like magnetization behavior as a function of temperature of ultrathin films are given which lead to the conclusion that stabilization of the magnetization at low temperature is a universal characteristic of ultrathin magnetic films. Comparison between ultrathin film and surface magnetic behavior is made. Evidence is given that the weakening of exchange coupling both at the surface of a bulk sample and across magnetic spacer layers between an ultrathin magnetic thin film and a bulk sample can be evaluated and dramatic effects due to minute quantities of non-magnetic nearest neighbors are demonstrated.
Magnetic Properties of Rare-Earth/Fe Multilayered Films with Artificial Superstructures
Authors: Shinjo Teruya , Mibu Ko , Ogawa Shinichi , Hosoito Nobuyoshi
Published: September 2012

By using UHV deposition technique, multilayered films consisting of Fe and rare-earth (Dy, Nd or Y) layers were prepared. Magnetic properties of Fe layers were investigated from 57Fe Mössbauer spectroscopy. From SQUID magnetic measurements, the behavior of rare-earth layers was studied. In Fe/Dy and Fe/Nd multilayers, there often exists a large perpendicular anisotropy. Mössbauer spectra evidenced that, in certain samples, the magnetization changes the direction, from in-plane at high temperature to perpendicular at low temperature. The origin of the perpendicular anisotropy is attributed to interface rare-earth atoms which are magnetically coupled with ferromagnetic Fe layers even at higher than their bulk Curie temperatures.
The Thermal Stability of Heavily Carbon-Doped GaAs Grown by Metalorganic Molecular Beam Epitaxy
Authors: Sohn Hyunchul , Weber E. R. , Nozaki S. , Konagai M. , Takahashi K.
Published: September 2012

Heavily carbon-doped GaAs thin films with a hole concentration of 5.8 × 1020 cm-3, grown by metalorganic molecular beam epitaxy (MOMBE), were annealed at 900°C for 30 minutes. The microstructural changes due to annealing were investigated by transmission electron microscopy. Electron diffraction study showed some evidence of carbon clustering on {111} in as-grown samples. A high density of precipitates was found in the annealed sample, together with a decrease of the lattice contraction and hole concentration. In the as-grown layer, misfit dislocations with only one type of Burgers vector were observed, while misfit dislocations with the several Burgers vectors were observed in [110] direction after annealing. The density of misfit dislocations in both <110> directions increased significantly even though the lattice contraction in carbon-doped GaAs decreased after annealing. A model is proposed to explain the change of misfit dislocation density in heavily carbon-doped GaAs layer.
Oxygen Related Lattice Defects in Silicon: Present Status
Authors: Bender Hugo , Vanhellemont Jan
Published: September 2012

The structural characterization of the oxygen related lattice defects formed under different thermal cycling conditions is discussed. The present understanding on the nature of rod-like defects and oxide precipitates is reviewed. Attention is given to the whole lattice defect spectrum which is induced by the oxygen precipitation. The influence of carbon and dopants on the defects is discussed.
High Resistivity GaSb and GaAs Produced by MBE Growth at Elevated Temperatures
Authors: Polyakov A. Y. , Milnes A. G. , Stam M. , Wilson R. G. , Fang Z. Q. , Rai-Choudhury P. , Hillard R. J.
Published: September 2012

In this paper we show that when grown by MBE at unusually high temperatures epitaxial layers of GaSb and GaAs are semi-insulating. In GaSb combination of Hall effect, TSC, SIMS and two probe resistivity profiling leads us to believe that high resistivity is due to production of midgap centers at elevated temperatures. No strong evidence of the prevalence of such midgap centers was obtained for high temperature GaAs layers and in this case we believe that high resistivity is associated with the formation of Ga-related precipitates acting as internal Schottky barriers.
Defect Structures in Heteroepitaxial InAs/GaAs and GaAs/InAs Grown by Atomic Layer Molecular Beam Epitaxy
Authors: Molina S. I. , Aragon G. , Garcia R.
Published: September 2012

A Transmission Electron Microscopy (TEM) study on ALMBE grown InAs/GaAs (001) is presented. The density and the types of defects contained in InAs and GaAs layers are clearly different. A relation between the planar defects in these layers and the compressive and extensive nature of the growth for each layer is found. Atomic Layer Molecular Beam Epitaxy (ALMBE) grown InAs layers possess a better quality of defects than other InAs layers grown on GaAs (001) by conventional MBE. Several ways of nucleation are presented as possible for explaining the existence of the different defects found in the studied heterostructure.
Effect of Electron Irradiation and Excess Cd on Ion-Assisted Doping of p-CdTe Thin Films
Authors: Kim D. , Fahrenbruch A. L. , Lopez-Otero A. , Bube R. H.
Published: September 2012

Ion-assisted doping of homoepitaxial p-CdTe films with low energy P ions (20 eV) deposited by vacuum evaporation has been investigated. In order to control the properties of the films, we applied low energy electron irradiation and Cd overpressure during the growth. We report the results of measurements of hole density, spectral response of Cr/p-CdTe Schottky barriers (to estimate the minority carrier diffusion length Lj). From Ld, we have found that the quality of the films is dependent on both the ion dose and the ion energy. By reducing the ion energy to 20 eV and applying electron irradiation and Cd overpressure, p-CdTe films with p = 1 × 10 17 cm−3 and Lp =0.35 μm were obtained. A p-CdTe film with p = 1016 cm−3 was obtained with a low ion energy of 10eV.
Application of Transmission Electron Microscopy to Solving Defect Issues in III-V Alloy Semiconductors and Devices
Authors: Ueda O.
Published: September 2012

In this paper we provide a review of materials issues in the III-V alloy semiconductor system and examine the role of such issues in the degradation of semiconductor lasers and LEDs.

Among the major materials issues are the formation of defects and thermal instability of the crystals; we will discuss both of these processes, giving relevant examples. It is convenient to divide crystal defects into two classes: interface defects are bulk defects. Among the former type of defects are stacking faults, V-shaped dislocations, dislocation clusters, microtwins, inclusions and misfit dislocations. Defects belonging to the second class include precipitates and dislocation loops. Thermal instability in crystals during growth also leads to structural imperfections which can affect device properties. One example is the formation of quasi-periodic modulated structures due to spi nodal decomposition of the crystal either at the liquid/solid interface or the growth surface. Another is the formation of ordered structure which also occurs on the growth surface through migration and reconstruction of deposited atoms.

We discuss optical device degradation in terms of three major degradation modes: rapid degradation, gradual degradation and catastrophic failure. In devices which degrade by rapid degradation, it is found that recombination-enhanced dislocation glide and climb are responsible. We examine the ease with which these phenomena occur in various hetero-structures and attempt to determine what the dominant parameters are. Gradual degradation takes place presumably due to recombination-enhanced point defect reaction in GaAlAs/GaAs-based optical devices. This degradation mode can be enhanced by the presence of stress due to lattice mismatch in the system. However, in InGaAsPAEnP-based devices, gradual degradation is not observed. In GaAlAs/GaAs DH lasers, catastrophic failure is found to be the result of catastrophic optical damage at a mirror or defect. Again, however, InGaAsP/InP DH lasers do not suffer from this form of degradation. In each degradation mechanism, the role of defects in the degradation and methods of elimination of degradation are discussed.
Rapid Structural Defect Mapping of Bulk II-VI Semiconductors Using White-Beam Synchrotron Topography and X-ray Rocking Curve Analysis
Authors: Marzio Don Di , Casagrande Louis G. , Lee Myung B. , Fanning Thomas , Dudley Michael
Published: September 2012

Nondestructive characterization techniques for substrates, epilayers, and device structures are becoming increasingly important in the semiconductor industry. Synchrotron-based white-beam x-ray topography, x-ray rocking curve measurements, and etch pit density were used to map the defect structure in a variety of CdTe and CdZnTe single crystal substrates, which are important for IR detector applications involving HgCdTe. Defects such as low angle grain boundaries have been successfully correlated using topography, rocking curves, and etch pit density, and twins have been observed using topography and rocking curves. The effectiveness of white-beam synchrotron topography for rapid and nondestructive defect analysis and substrate screening is discussed.
Relaxation Defect Characterization of RTCVD Si1-xGex/Si Heterostructjres by Electrical and Optical Techniques
Authors: Souifi A. , Bremond G. , Benyattou T. , Guillot G. , Dutartre D.
Published: September 2012

Photoluminescence (PL) and deep level transient spectroscopy (DLTS) measurements have been carried out on Si1-xGex/Si heterostructures and Si/Si1-xGex/Si double heterostructures with fully strained or partially relaxed layers (0%<xGe<20%) grown by chemical vapor deposition using rapid thermal processing (RTCVD). This study reports strong PL and DLTS results connected to the establishment of relaxation defects in the SiGe layer and at the heterointerface which appear when the layer starts to relax. Strong broad PL bands (defect related) and sharp lines (similar to dislocation related D-lines on Si) have been detected and connected to this relaxation process. These PL results are strengthened by the clear observation, using DLTS experiments on relaxed layers, of interface traps with a maximum energy around Ev + 0.5eV resulting from the presence of misfit dislocations at the SiGe/Si hetero-interface and a deep level at Ev + 0.38eV related to dislocations or relaxation defects in the SiGe layer. Moreover, low temperature PL excitonic transition reported on Si/Si1-xGex/Si double heterostructures is described as a good tool to investigate the relaxation process which occurs in these heteroepitaxial layers.
Monoenergetic Positron Beam Studies of Oxygen in Single Crystal Silicon - Stress Induced Clustering of Oxygen Atoms in Silicon
Authors: Nagai R. , Takeda E. , Tabuki Y. , Wei L. , Tanigawa S.
Published: September 2012

A monoenergetic positron beam has been used to investigate the state of interstitial oxygen in Czochralski (CZ)-grown Si with either thermally grown S1O2 (100 nm thick) or silicon oxide (p-SiOx) deposited by plasma enhanced chemical vaper deposition technique on the surface. Both the growth of thermal SiO2 and the deposition of SiOx film resulted in a reduction of the doppler-broadening line shape parameter (S-parameter) for the positron annihilation in the bulk silicon region. Annealing at 450δC, the removal of oxide overlayer or long-term aging at room temperature caused the S-parameter to return to its intrinsic value. It was thought that tensile stress in silicon, induced by the thermal oxidation or the deposition of SiOx films which had compressive internal stress themselves, enhanced the rearrangement of oxygen atoms and caused the formation of oxygen clusters in silicon crystal. Oxygen interstitial clusters can trap positrons leading to the lower S-parameter value for annihilation in the bulk silicon region, because of large overlap with core electrons. The above results suggest that oxygen atoms can absorb lattice strain by clustering and thus prevent the generation of dislocations against external stress in the Si lattice. This results yield an additional explanation of the high mechanical strength of CZ Si crystal.
Optical Study of the Fe3+-Related Emission at 0.5 eV in InP:Fe
Authors: Pressel Klaus , Bohnert G. , Dörnen A. , Thonke K.
Published: September 2012

The 0.5 eV (2.5 μm 4000 cm1) emission band in InP has been studied by optical spectroscopy. By the use of Fourier-transform-infrared photoluminescence we have been able to observe at least a three-fold fine structure in the zero-phonon transitions at ∼ 4300 cm−1 which are studied at different temperatures. Based on the fine structure and the long decay time of 1.1 ms we ascribe the 0.5 eV emission to the 4T1 → 6A1 spin-flip transition of Fe3+. The excitation spectrum of this Fe3+-related emission shows a characteristic fine structure at ∼ 1.13 eV which belongs to a charge-transfer process of the type: Fe3+ + hv (1.13 eV) → [Fe2+, bound hole]. We discuss the excitation mechanism of the 0.5 eV emission by charge-transfer states and compare the results with an emission at 3057 cm1 in GaAs, which we attribute to the same Fe3+ transition (decay time: 1.9 ms).
The Interfacial Reactions in Ti/Si and Ni/Si Systems Observed by a Monoenergetic Positron Beam
Authors: Tanigawa S. , Wei L. , Tabuki Y.
Published: September 2012

The formation of suicides via the thin-film deposition of transition metals onto Si substrates has been investigated by a monoenergetic positron beam. The Doppler broadened spectra of annihilation radiations in the as-deposited state and the silicide-formed state of the Ti/Si and Ni/Si systems were measured as a function of the incident positron energy between 0.1 keV and 30 keV. From the depth dependence of positron annihilation characters, the diffusion length of positron was determined on the basis of one dimensional diffusion models. In the case of the Ti/Si, the formation of the suicides did not induce the shortening of positron diffusion length in Si substrate. On the contrary, the diffusion length of positrons in formed suicides was very short indicating the presence of a great number of positron traps in suicides. From this fact, the moving species during the silicidation may be Ti atoms. On the other hand, in the case of Ni/Si, the silicidation induced a very short diffusion length of positrons in the Si substrate. On the contrary, the diffusion length in the formed suicide is long to a comparable extent expected defect-free metals. From this fact, the moving species may be Si atoms. In the present parer, the first report on the microscopic observation of Kirkendall effect in metal/Si systems by means of a monoenergetic positron beam will be given.
Electron Irradiated InP: A Positron Annihilation Study
Authors: Bretagnon T. , Dannefaer S. , Kerr D.
Published: September 2012

Positron lifetime measurements show that electron irradiation produces indium vacancy related defects in InP. Divacancies are also found in semi-insulating and lightly doped p and n-type materials. Temperature investigations show a change in the divacancy charge state.
The Study of Si, Se and O-Implanted GaAs by Slow Positrons
Authors: Fujii S. , Shikata S. , Wei L. , Tanigaw S.
Published: September 2012

Variable-energy (0–30keV) positron beam studies have been carried out on 200 keV Se-implanted and 70 keV Si-implanted GaAs specimens before and after annealing for electrical activation. From the measurements of Doppler broadened profiles as a function of incident positron energy, it was found that vacancy clusters with high concentration were introduced in the annealed specimen after Se implantation. From the parallel measurement of electrical characteristics, a higher activation efficiency was found for the higher concentration of vacancy clusters. That fact implies that electrons supplied by the activation of Se also convert the charge state of As vacancies from positive to negative. In contrast, no vacancy clusters were introduced in the Si-implanted GaAs. On the other hand, oxygen clustering was found in annealed specimen after O implantation.
The Effect of Hydrogenation on the Electrical Properties of Crystalline Silicon
Authors: Pankove Jacques I.
Published: September 2012

Hydrogen ties Si dangling bonds at defects as well as near impurities. Defect passivation leads to dramatically lower surface recombination and increased minority carrier lifetime. Dopant neutralization increases the resistivity of the crystal and the mobility of carriers. The neutralization of donors and acceptors is optimum at different temperatures. Deep levels can also be neutralized.
Local Bonding Structure of Hydrogen in Crystalline Silicon: NMR and Tem Studies
Authors: Boyce J. B. , Johnson N. M. , Ready S. E. , Walker J. , Anderson G. B.
Published: September 2012

Nuclear magnetic resonance (NMR) and transmission electron microscopy have been used to obtain information on the local structure of deuterium in single-crystal silicon, both for deuterated, phosphorous-doped Si that contains platelet-structured defects and for deuterated boron-doped silicon. In both cases, the NMR spectrum consists of two components, a narrow doublet and a central, unsplit line. The doublet arises from D bonded to Si with the Si-D bond along the <111> directions. The central line, which contains more D than does the doublet, is ascribed primarily to molecular D2 that resides in regions of the crystal where translation and tumbling are inhibited and possibly to some D in weak Si-D bonds.
Passivation of Surface and Bulk Defects in InP
Authors: Balasubramanian Sathya , Kumar Vikram , Balasubramanian N. , Premachandran V.
Published: September 2012

The effect of sulfur and hydrogen plasma treatment on the Schottky barrier and photoluminescence (PL) properties of p-InP is reported. Both the treatments increase the barrier height of Au/p-InP diodes and band to band PL. This is explained as being due to a shift in the surface fermi level position towards the P vacancy related pinning level in the top half of the band gap. The H+ treatment passivates the shallow and deep levels as observed from the C-V depth profile and PL respectively.
Hydrogen Passivation and Reactivation of DX Centers in Se-Doped and Si-Doped AlGaAs - - A Comparison
Authors: Roos G. , Johnsons N. M. , Herring C. , Harris J. S.
Published: September 2012

The effect of hydrogenation on DX centers was evaluated for both Si- and Se-doped AlxGa1-xAs (x=0.26 and 0.23). MBE-grown AIGaAs:Si and MOCVD-grown AIGaAs:Se epilayers were hydrogenated with either monatomic hydrogen or deuterium from a remote plasma at 250°C for 1h. The passivation and subsequent reactivation kinetics were studied with C-V and DLTS techniques. Reactivation was investigated in the space-charge layer of Schottky diodes under different bias conditions. While the Group VI and Group IV deep donors respond similarly to passivation, they display significantly different reactivation kinetics, with thermal dissociation energies of 1.5 eV and 1.2 eV for Se-H and Si-H, respectively. These values are close to the energies previously determined for reactivation of the Si and Se shallow donors in both AIGaAs and GaAs. Therefore, they are not significantly dependent on the Al concentration (x < 0.30) even for donors residing on the As sublattice. Our results are consistent with the Chang-Chadi model of DX centers.
Passivating Complexes in Cd Doped G a As and InP: Microscopic Properties and Electrical Effects
Authors: Moriya N. , Deicher M. , Kalish R. , Keller R. , Magerle R. , Pfeiffer W. , Pross P. , Skudlik H. , Wichert Th. , Wolf H. , Collaboration Isolde
Published: September 2012

Perturbed Angular Correlation (PAC) and Hall measurements were used to investigate the stability of the passivating Cd-H complex in GaAs after low energy H implantation (150 eV, 1014 cm−2) at 300 K. From the observed Cd-H pair formation and reduction of hole concentration it is deduced that about 10 % of the implanted H atoms form pairs with the Cd atoms. The influence of the dopant depth profile on the apparent stability in zero bias isochronal annealing experiments is reported. After H loading a reduction of carrier mobility is observed, which is stable up to about 400 K. The formation of Cd-H pairs after low energy H implantation into InP was studied by PAC. By measuring the fraction of pairs in an isochronal annealing experiment, the stability of the pairs is deduced yielding a dissociation energy of ED = 1.8 (1) eV.
Comparison of Trapping States at SiO2/Si Interfaces on si(100), (110), and (111) Prepared by Plasma-Assisted Oxidation and Oxide Deposition, and by Exposure to Atomic H Prior to Oxidation and Deposition
Authors: Yasuda T. , Ma Y. , Habermehl S. , Lucovsky G.
Published: September 2012

S1O2 layers, ∼ 15 nm thick, were formed on Si (100), (110), and (111) surfaces by a low-temperature, 200–300°C, plasma-assisted oxidation/deposition process sequence. The distribution of the trap density at the S1O2/Si interface, and in the Si band-gap, Dit, was deduced from capacitance-voltage, C-V, measurements. The values of Dit at midgap varied with crystal orientation in a similar way as in thermally grown oxides. In addition, the low-temperature oxides displayed a characteristic and intrinsic dangling bond state, the so-called Pb center, at ∼0.3 eV above the Si valence-band edge. Samples exposed to atomic H prior to the oxidation and deposition steps, showed an increase in Dit due to a roughening of the Si surfaces, which produced additional broad bands of defect states, at ∼0.5 and ∼0.7 eV above the Si valence-band edge.
Evaluation of Microdefects in As-Grown Silicon Crystals
Authors: Takeno H. , Ushio S. , Takenaka T.
Published: September 2012

Microdefects, revealed as ‘flow patterns’ by preferential etching using Secco's etchant, in as-grown silicon crystals have been investigated by means of a transmission electron microscopy and a preferential etching. In as-grown CZ crystals, grown at the pulling speeds of 0.4 or 1.4 mm/min, dislocation loops and clusters were observed with TEM. The dislocation loops in both crystals are interstitial type. From a thermal behavior of flow patterns by heat treatments, we confirmed that the defects revealed as flow patterns in CZ crystals do not have a similar nature of that in D-defect region of FZ crystals.
The Effect of Vacancies Grown into Silicon on Gold Diffusion
Authors: Graupner R. K. , Van Vechten J. A. , Harwood P. , Monson T. K.
Published: September 2012

We propose a generalized model for gold diffusion in silicon based on the effect of the high concentrations of vacancies and vacancy complexes in the as-grown silicon. The monovacancy profiles calculated using this model are identical to the substitutional gold profiles calculated using the kick-out model. We deposited Au on commercial float zone Si in a vacuum system after the Si had reached the diffusion temperature (1233 K) and had been annealed in various ways. Contrary to previously published reports, we find the electrically active Au with a nearly one-sided profile when the Au is deposited on samples which were preannealed in vacuum. We conclude that annealed silicon surfaces lack the imperfections needed to make them effective sources or sinks for vacancies or self-interstitials. We propose that this can cause a high degree of supersaturation in the as-grown silicon crystal since the point defects cannot annihilate at the surfaces to maintain equilibrium as the crystal is cooled.
Enhancement of Long-Wavelength Photoluminescence Due to Heat-Treatment in Si-Doped GaAs
Authors: Suezawa M. , Kasuya A. , Nishina Y. , Sumino K.
Published: September 2012

Highly officient radiative recombination even at room temperature was found at a wavelength of about 1.3 μm in heat-treated Si-doped GaAs. The range of Si concentrations and the condition of heat-treatment to yield this intense luminescence were determined. Excitation spectra of the PL lines suggest that such PL lines are related to pairs of Si-donor and Si- acceptor and such pairs combined with gallium vacancies.
Formation Mechanism and Recombination-Enhanced Dissociation of a Hydrogen-Carbon Complex in Silicon
Authors: Kamiura Yoichi , Hashimoto Fumio , Yoneta Minoru
Published: September 2012

Wc have found that chemical etching induced an electron trap E3 (0.15) into n-typc Si. We attribute this trap to a hydrogen-carbon complex on the basis of available experimental data. By measuring DLTS depth profiles of the E3 trap, we propose a model of the formation mechanism of the hydrogen-carbon complex as follows. Hydrogen atoms arc adsorbed on the Si surface to terminate Si dangling bonds during chemical etching, and after the etching some unstably adsorbed ones diffuse into the near-surface region of silicon and are trapped by carbon to form the complex. The E3 trap is stable up to 100δC in the dark but is annihilated by the illumination of band gap light around 250K only outside the depletion layer of the Schottky structure. This provides unambiguous experimental evidence for the recombination-enhanced dissociation, in which the electronic energy released by the electron-hole recombination at the E3 level is converted into local kinetic energy of hydrogen to be released from carbon.
Process Physics of the Iron-Boron Pair Recombination and Dissociation in p-Type Silicon
Authors: Wuaranakula W.
Published: September 2012

The process physics of the iron-boron pair recombination and dissociation in p-type silicon at temperatures below 300°C was studied. The result indicates that the recombination and dissociation processes depend strongly upon the relative position of the ionization energy of interstitial iron Efe+ and the Fermi level Ef. At temperatures T < (Efe+ - Ep)/k, the pairing reaction obeys first-order reaction kinetics while at temperatures T > (EFe+ - Ep)/k, an equilibrium between neutral and charged defect species prevails.
Evidence for Metastabile State of DX Center in AxGa1-xAs
Authors: Ghosh Subhasis , Kumar Vikram
Published: September 2012

Photo-Deep Level Transient Spectroscopy with 1.38 eV light reveals a new level with thermal activation energy 0.2 eV of DX centers in silicon doped Alx Ga1-xAs (x = 0.26) for the first time. The observation of this level directly proves the negative-U properties of DX centers and the existence of thermodynamically metastable state DX.
Defect- Impurity Interaction in Irradiated n-GaAs
Authors: Kdrshunov F. P. , Prokhorenkd T. A. , Sobolev N. A. , Mjdriavtseva E. A.
Published: September 2012

The creation of radiation defects (RD's) and their interaction with shallow impurities in 3–4 MeV electron irradiated n-GaAs have been studied by means of photoluminescence (PL) and Hall effect. The irradiations were carried out at sample temperatures ranging from Ti = 30 to 500°C. It has been found for the first time that for high fluences at room temperature the shallow donor concentration starts to decrease. The behaviour of the carrier concentration (n), mobility (μ)and of the concentrations of the shallow acceptors C (As) and Ge (As) has been studied on irradiation and annealing. It was found that the behaviour of the As vacancy govern the main annealing processes observed.
Metallic Impurities in n- and p- Type Silicon: Dlts Studies
Authors: Agarwal Aditya , Radzimski Z. J. , Buczkowski A. , Shimura F. , Rozgonyi G. A.
Published: September 2012

Deep level majority and minority carrier traps in p+/n and n+/p junction diodes have been investigated. The junctions were fabricated on n- and p- type silicon which was intentionally and uniformly doped with heavy metals Cr, Fe, Ni, and Au during Czochralski crystal growth. The activation energies of the traps in these devices has been determined using a computer based Deep Level Transient Spectroscopy system which stores and analyzes entire capacitance-time transients. The capacitance-time data sets have been analyzed using the standard rate-window method as well as by a new algorithm which is able to test for the existence of a single exponential. The new algorithm has shown that only one of the ten traps measured contained a single exponential. Rate-window analysis of all the data sets, however, yielded energy levels based on the expectation of a single-exponential, despite the inherent non-exponentiality of the transients. Implications on the reliability of results obtained by the rate window method have been discussed. Possible reasons for the observed non-exponentiality in the data have been suggested based on a study of simulated data.
The Influence of Stresses on the Surface-Near Defect Structure
Authors: Reiche M. , Nitzsche W.
Published: September 2012

An external stress field, induced at the film edge of a nitride layer, affects the defect generation in the surface-near region. Nucleation and growth of oxide precipitates and/or the generation of dislocations result in the reduction of the width of the denuded zone. The defect formation is discussed in dependence on the stress, gettering technique (annealing conditions), and on the initial oxygen concentration. The effect on electrical parameters is shown. The investigations prove that an additional oxide film (SiO2/Si3N4 films) does not relax completely the tensile stress induced by the nitride layer.
Electric Degradation and Defect Formation of Silicon Due to Cu, Fe, and Ni Contamination
Authors: Naito Shunta , Nakashizu Tsuneo
Published: September 2012

Electric degradation of silicon wafer due to Cu, Fe, and Ni contamination has been studied using MCZ with low oxygen and CZ wafers. In the cases of Cu and Ni contamination, the electric properties depended on the characteristics of the starting wafers,. especially the type of conductance. The behavior of these metals in the low temperature region played an important role to understand the electric properties. On the contrary, no difference between p- and n-type wafers was observed in Fe contamination in our experiment.

The surface defects were observed with high density in the MCZ wafers in Cu contamination. These defects were sensitive to the degradation of the MOS C-t generation lifetime. Making use of this relation, the efficiency of the extrinsic gettering was evaluated.
Evidence for a defect-assisted low resistive conductivity in cw laser beam mixed Au/Te/Au/GaAs contacts.
Authors: Watté J. , Silverans R. E. , Münder H. , Wuyts K.
Published: September 2012

CW laser beam mixed Au/Te/Au/n-GaAs contacts have been studied by RBS, Möss-bauer and Raman spectroscopy. For both low and high laser power mixing, resulting in respectively Schottky-type and ohmic contacts, the formation of non-uniformly dispersed Ga2Te3 crystallites was observed. However, for the ohmic contacts the formation of a high density of defect complexes in the GaAs surface layers was revealed. The experimental results suggest that the ohmic conduction mechanism is based on a hopping or a defect assisted tunneling process through the contact zone, consistent with the amorphous/highly defective heterojunction model.
Heat-Treatment Induced Defects in Cz-Silicon
Authors: Dannefaer S. , Bretagnon T. , Abdurahman K. , Kerr D. , Hahn S.
Published: September 2012

Positron lifetime results show that vacancies can be retained after growth of Czochralski silicon at concentrations of ∼x1016/cm3. Rapid thermal annealing as well as furnace annealing increase the vacancy concentration. The vacancies are predominantly trapped by oxygen interstitial clusters in lightly B-doped materials, and these complexes appear to have temperature dependent configurations which can be quenched-in by rapid cooling. Heavy Sb doping results in trapping of vacancies by the Sb impuritie