Showing papers in "Physica Status Solidi (c) in 2004"
TL;DR: The thermal conductivity of single crystals of silicon with two different isotopic compositions: natural and 99.983% enriched 28Si, was investigated in the temperature range from 0.5 K to 300 K as discussed by the authors.
Abstract: The thermal conductivity κ(T) of single crystals of silicon with two different isotopic compositions: natural and 99.983% enriched 28Si, was investigated in the temperature range from 0.5 K to 300 K. The enriched 28Si sample has very high thermal conductivity maximum of 290 W cm–1K–1 at Tmax = 26.5 K, about 7.5 times higher relative to the conductivity of natSi with natural isotope abundance. The isotope effect decreases with temperature increase, being 10 ± 2% at room temperature. The data are discussed briefly within the Ambegaocar's theory of isotope effect. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
104 citations
TL;DR: In this article, a novel material: nanostructured CdS:O film prepared at room temperature by rf sputtering, and its application in CdTe solar cells was reported.
Abstract: In this paper, we report on a novel material: nanostructured CdS:O film prepared at room temperature by rf sputtering, and its application in CdTe solar cells The CdS:O film has a higher optical bandgap (25–31 eV) than the poly-CdS film and a nanostructure; the bandgap increases with an increase of oxygen content (from ∼4 at% to ∼23 at%) and a decrease of grain size (from about a few hundred A to a few tenths A) Our results have also demonstrated that the higher oxygen content presented in the nanostructured CdS:O films can significantly suppress the Te diffusion from the CdTe into the CdS film and the formation of a CdS1−yTey alloy with a lower bandgap that results in poor quantum efficiency in the short-wavelength region The preliminary device results have demonstrated that the Jsc of the CdTe device can be greatly improved by exploiting the thin nanostructured CdS:O film, while maintaining higher Voc and FF We have fabricated a CdTe cell demonstrating an NREL-confirmed total-area efficiency of 155% (© 2004 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim)
88 citations
TL;DR: In this article, the authors give an example by designing a refractive index around 1.465 at 1.557 μm wavelength with magnetic fluids composed of various carriers and particles, that could play an important role in optical fiber communication.
Abstract: Magnetic fluid is a type of colloid consisting of magnetic nano-particles dispersed in a liquid carrier with the aid of surfactants and Brownian motion. Thus, the optical properties of magnetic fluids can be manipulated through careful selection of magnetic particles and carriers. In this work, we give an example by designing a refractive index around 1.465 at 1.557 μm wavelength with magnetic fluids composed of various carriers and particles, that could play an important role in optical fiber communication. In addition, we also show how to achieve a desired flexibility in the tunable refractive index with externally varying fields by adopting suitable magnetic fluid films. These results reveal the feasibility of developing index-match or index-tunable devices using magnetic fluids. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
70 citations
TL;DR: A detailed composition, intensity and temperature dependent photoluminescence (PL) study of CuInSe 2 has been performed to obtain data on defects, directly comparable to the defects in CuGaSe 2, prepared under the same conditions as mentioned in this paper.
Abstract: A detailed composition, intensity and temperature dependent photoluminescence (PL) study of CuInSe 2 has been performed to obtain data on defects, directly comparable to the defects in CuGaSe 2 , prepared under the same conditions. Epitaxial films are grown by metal organic vapour phase epitaxy on GaAs. The PL study reveals three shallow defects, which are responsible for the doping behaviour in CuInSe 2 : two acceptors, 40 and 60 meV deep, and a donor, approximately 12 meV deep. The shallower acceptor dominates for low or no Cu-excess, whereas the deeper one dominates material grown under high Cu-excess. These defects and their compositional dependence are the same as observed in CuGaSe 2 . Thus no fundamental difference concerning the shallow defects exists between these two materials.
67 citations
TL;DR: In this article, it was shown that cyanide treatment has an effective role in passivation of defects in Cu2O, in analogy to hydrogen passivation, and that the observed improvement in the electrical rectification of the ZnO/Cu2O heterojunctions is attributable to the defect passivation near the hetero-interface.
Abstract: Polycrystalline n-ZnO/p-Cu2O heterojunctions were fabricated by reactive sputtering for photovoltaic applications Although electrical rectification was not reproducibly obtained in the as-grown samples, rectification was observed in the samples fabricated with cyanide treated Cu2O We have previously shown that cyanide treatment has an effective role in passivation of defects in Cu2O, in analogy to hydrogen passivation It is, therefore, believed that the observed improvement in the electrical rectification of the ZnO/Cu2O heterojunctions is attributable to the defect passivation near the hetero-interface The effectiveness of the cyanide treatment and the importance of defect passivation in ZnO/Cu2O heterojunctions are presented (© 2004 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim)
60 citations
TL;DR: In this paper, the authors show that ion bombardment is responsible for the formation of a disorderd subsurface layer while deposition on a cooled substrate allows us to trap the silicon nanocrystals and to prevent their growth, thus leading to nanocrystalline thin films.
Abstract: We review current models and propose new approaches for the production of silicon thin films by low temperature plasma processes. Growth models have often been borrowed from those developed for hydrogenated amorphous silicon and are based on surface diffusion of SiH3. However, in situ growth studies have also pointed out the fast diffusion of hydrogen and its role in the crystallization of the film through subsurface reactions. Moreover, ions and silicon nanocrystals can also play a crucial role in microcrystalline silicon deposition. We show that ion bombardment is responsible for the formation of a disorderd subsurface layer while deposition on a cooled substrate allows us to trap the silicon nanocrystals and to prevent their growth, thus leading to nanocrystalline thin films. The deposition at 200 °C on substrates with a low density of surface defects allows for the surface mobility of the nanocrystals and their agglomeration to form large grains, thus resulting in polycrystalline silicon thin films. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
58 citations
TL;DR: In this paper, the influence of barrier thickness and Alconcentration on the current across AlGaN barriers is investigated experimentally and compared to model calculations, and the effect of polarization fields on the electronic properties of single and double barrier heterostructures is discussed and experimental results are reviewed.
Abstract: We present a systematic study of vertical transport in AlGaN/GaN heterostructures. The influence of barrier thickness and Al-concentration on the current across AlGaN barriers is investigated experimentally and compared to model calculations. The effect of polarization fields on the electronic properties of single- and double barrier heterostructures is discussed and experimental results are reviewed. AlN/GaN double barrier RTD structures are fabricated under optimized growth conditions. Experimental analysis of their electronic properties reveals indications for resonant tunneling in the low forward bias regime. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
52 citations
TL;DR: In this article, the dependence of the Raman peak frequencies and amplitudes upon the thickness of the silicon membrane is interpreted as acoustic phonons in an acoustic cavity, and it is shown that these acoustic phonon are confined.
Abstract: Confined acoustic phonons in Silicon-on-insulator membranes have been observed by means of low frequency Raman scattering. The dependence of the Raman peak frequencies and amplitudes upon the thickness of the silicon membrane is interpreted as acoustic phonons in an acoustic cavity. The analysis confirms that these acoustic phonons are confined. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
47 citations
TL;DR: In this paper, a GaN-based blue-violet laser with a kink-free output power of higher than 150 mW has been successfully realized by adopting a new ridge structure and appropriately designing the beam divergence.
Abstract: GaN-based blue-violet lasers with a kink-free output power of higher than 150 mW have been successfully realized by adopting a new ridge structure and appropriately designing the beam divergence. The new ridge structure is a narrow 1.4 μm ridge covered with a stacked layer of Si on SiO2 and the beam divergence half-angles parallel and perpendicular to the junction plane are set at 8° and 21°, respectively. These lasers have been operating stably for more than 500 h under 130-mW pulsed operation at 60 °C. The empirical activation energy of device lifetime under 30-mW continuous-wave operation is 0.32 eV. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
39 citations
TL;DR: In this paper, computer simulations of the hopping relaxation of excitons were carried out to provide an important and reliable information on the energy shape of the density of states and also the energy range in which localized states for exciton are distributed.
Abstract: Exciton photoluminescence (PL) in a GaInNAs/GaNAs quantum well was measured in the temperature range from 15 K to 300 K. Two striking features of the PL were observed: the nonmonotoneous temperature dependence of the Stokes shift and the abrupt increase of the PL linewidth in a rather narrow temperature range. These features are known to be strong indications of the hopping relaxation of excitons via localized states distributed in space and energy. Computer simulations of the hopping relaxation of excitons were carried out. Comparison between the simulation results and the experimental data provides an important and reliable information on the energy shape of the density of states and also on the energy range, in which localized states for excitons are distributed. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
38 citations
TL;DR: The phase constitution and microstructure of NiFe2O4 powders prepared by a sol-gel autocombustion route have been studied in this article, where the results show that different Fe/Ni ratios in the starting solution and different calcination affect the crystal size of the synthesized powder and the phase constitution.
Abstract: The phase constitution and the microstructure of NiFe2O4 powders prepared by a sol-gel autocombustion route have been studied in this research. Amorphous gels, as-burnt powders with a varying Fe/Ni ratio and calcined powders at temperatures between 600–1000 °C for 1h, were investigated by using DTA/TG, XRD and SEM techniques. The results show that different Fe/Ni ratios in the starting solution and different calcination affect the crystal size of the synthesized powder and the phase constitution. SEM micrograph also shows a particle size less than 100 nm. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: The dominant relaxation mechanism of SRS-active Ag(ν1) vibronic modes in CaMoO4 and PbMoO 4 molecular ionic crystals was found to be the combination of two relaxation processes: the two-phonon splitting and the dephasing processes as discussed by the authors.
Abstract: The dominant relaxation mechanisms of SRS-active Ag(ν1) vibronic modes in CaMoO4 and PbMoO4 molecular ionic crystals were found to be the combination of two relaxation processes: the two-phonon splitting and the dephasing processes. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, the present status of recently developed ab-initio as well as semi-empirical electronic structure methods that are particularly suited for semiconductors and mesoscopic semiconductor structures is reviewed.
Abstract: This paper reviews the present status of recently developed ab-initio as well as semiempirical electronic structure methods that are particularly suited for semiconductors and mesoscopic semiconductor structures. In assessing each method, we provide some additional and hitherto unpublished details about its implementation. In the first part of the paper, we discuss two important extensions of the local density functional theory, the screened-exchange and the exact exchange method namely. We proceed with a discussion of the relativistic local density method that is essential for a prediction of spin-related phenomena in semiconductors. Finally, we review a rather complete and extensve implementation of the envelope function approach for arbitrary three-dimensional nanometer device structures.
TL;DR: In this paper, a cubic cubic Ni-Zn ferrite phase with a size of 15 nm and saturation magnetization of 44 emu/g at room temperature was synthesized by a low temperature method.
Abstract: Polycrystalline Ni-Zn ferrite, with a well-defined composition, $Ni_{0.8}Zn_{0.2}Fe_{2}O_4$, synthesized by a low temperature method showed the formation of a cubic ferrite phase with a crystallite size of 15 nm and saturation magnetization of Ms ≈ 44 emu/g at room temperature. When calcined at higher temperatures (up to 1200 oC) the magnetization increased continuously to Ms ≈ 67 emu/g. To understand the magnetic nature of the cubic ferrite phase formed at a temperature as low as 80 oC, 57 Fe Mossbauer spectra were recorded for samples annealed at three different temperatures, without any external magnetic field, and with an external field of $H_ext$ = 5 T, at 4.2 K. The spectral parameters at room temperature, namely, isomer shift, quadrupole splitting and hyperfine field, confirmed the presence of ultrafine superparamagnetic crystallites of Ni-Zn ferrite. The Mossbauer spectra at 4.2 K revealed spin relaxation effects resulting in very broad sextets, characteristic of ultrafine crystallites. The Mossbauer spectra recorded at 4.2 K and $H_ext$ = 5 T showed well resolved two sextet pattern with characteristic hyperfine interaction parameters of the cubic ferrite phase.
TL;DR: In this paper, the authors presented a device concept for long-wavelength vertical-cavity surface-emitting lasers (VCSELs) in the InGaAlAs/InP material system incorporating a buried tunnel junction (BTJ).
Abstract: In this paper we present a device concept for long-wavelength vertical-cavity surface-emitting lasers (VCSELs) in the InGaAlAs/InP material system incorporating a buried tunnel junction (BTJ). A major issue of long-wavelength VCSELs is the dissipation of heat because of the low thermal conductivity of ternary and quaternary alloys. With the BTJ-VCSEL, a significant reduction of the thermal resistance is achieved by the use of a hybrid backside mirror made of a stack of amorphous dielectrics with Au-coating and the monolithic integration of a heat sink. These provide improved heat sinking capability compared to a conventional epitaxial semiconductor DBR. In addition, the tunnel junction facilitates a substitution of most of the p-doped layers by n-doped material, reducing heat generation due to ohmic losses. These features significantly improve the VCSEL characteristics. At 1.55 μm wavelength, we demonstrated single-mode cw-output powers of 1.7mW at room temperature [1], multi-mode cw-output powers of 7mW [2], laser operation up to heat sink temperatures of 110 °C [2], and optical data transmission with 10 Gbit/s and low bit error rates [3]. These are record values to the best knowledge of the authors.
Using strained quantum wells, the emission wavelength can be tailored to any value in the range between 1.3 μm and 2.0 μm [4], sample results are presented for the telecommunication wavelengths 1.3 μm and 1.55 μm, 1.8 μm, and the currently upper limit of 2.0 μm. The slight wavelength tuning with driving current is brought about by the tiny volume of the devices and makes VCSELs ideal components for tunable diode laser absorption spectroscopy (TDLAS) [5, 6]. The maximum detuning typically reaches 4 nm (≙500 GHz). (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, the diameters of these particles were estimated from X-ray diffraction patterns as ranging from 2 to 6 nm, and magnetic parameters, such as saturation magnetization (Ms), permeability (μ), and coercivity (Hc), were determined from M-H curves.
Abstract: Ni(1-x)Zn(x)Fe2O4 (0≤x≤1) mixed ferrite nanoparticles encapsulated with amorphous-SiO2 were prepared by a wet chemical method. The diameters of these particles were estimated from X-ray diffraction patterns as ranging from 2 to 6 nm. Magnetization measurements were performed for each obtained sample under a ±50 kOe field. Magnetic parameters, such as saturation magnetization (Ms), permeability (μ) and coercivity (Hc), were determined from M-H curves. The relationship between saturation magnetizations Ms and the Zn concentration was almost similar to that between the saturation magnetization and Ni-Zn ferrite bulk crystal, however, the absolute values of Ms of the nanoparticles were about 30 % smaller than those of bulk crystal. The decrease of Ms in the nanoparticle system might be attributed to the canting surface spins or ion distributions. is the abstract. You may use this Word document template to write your article. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, a new model for avalanche carrier multiplication in amorphous semiconductors is proposed, which does not employ the Shockley's lucky-electron ansatz according to which a free carrier gains the energy from electric field in a ballistic motion.
Abstract: A new model for avalanche carrier multiplication in amorphous semiconductors is suggested. In contrary to previous considerations, the model does not employ the Shockley's lucky-electron ansatz according to which a free carrier gains the energy from electric field in a ballistic motion. We show that the majority of free carriers reaching the ionization threshold energy do so by drift, not ballistically. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this article, Raman scattering and IR-reflection have been performed for in-depth investigation of He-implanted LiNbO3, showing substantial changes, from the top surface up to the buried nuclear stopping layer acting as optical barrier, in terms of crystal structure, chemical bonding and electro-optical properties.
Abstract: Raman scattering and IR-reflection have been performed for in-depth investigation of He-implanted LiNbO3. The obtained results clearly demonstrate substantial changes, from the top surface up to the buried nuclear stopping layer acting as optical barrier, in terms of crystal structure, chemical bonding and electro-optical properties of the waveguide. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, a single crystalline sphere was considered to calculate the relative contributions of the confined modes to the Raman scattering, and the second harmonic of these confined modes was also registered.
Abstract: CdS nanoparticles with average radius Ro = 2.2 nm have been investigated by Raman scattering measurements. The nanoparticles, synthesized using aqueous solution precipitation, are small enough to show effects due to confinement. In the Raman spectra of CdS nanoparticles an asymmetric Raman line was observed. The dominant line was at about 300 cm–1 having asymmetric broadening for ω < 300 cm–1. We considered a single crystalline sphere to calculate the relative contributions of the confined modes to the Raman scattering. The second harmonic of these confined modes was also registered. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, a geometrical model of the growth of mixed phase Si is presented, connecting the macroscopically observed transport properties and the crystallinity, hydrogen content, grain size and grain boundaries.
Abstract: Silicon thin films grown near the boundary between the amorphous/microcrystalline growth offer superior properties for industrial applications. Series of silicon samples, in which crossing of this transition region was achieved by changing a single technological parameter (dilution of silane in hydrogen, deposition temperature, sample thickness) were used to test our model of transport, connecting the macroscopically observed transport properties and the crystallinity, hydrogen content, grain size and grain boundaries. Microscopic study by AFM led to the formulation of the geometrical model of growth of mixed phase Si. The demand for research of microcrystalline or polycrystalline silicon prepared at low substrate temperatures is stimulated by the use of cheap plastic substrates. In addition to a direct deposition an alternative technology, such as metal-induced crystallization supported by the electric field is discussed. Possible future application of thin silicon films, for example in a “nanolithography”, is also shown. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this article, the experimental methods of the determination of junction temperature and thermal resistance in GaN-based LEDs are described, and a micro thermocouple is embedded into the epoxy package for the investigation of its size effects on thermal behavior.
Abstract: This paper reports on the experimental methods of the determination of junction temperature and thermal resistance in GaN-based LEDs. For the direct temperature measurement and investigation of thermal distribution on the operating LED chip, nematic liquid crystal thermographic technique was employed. Hot spot was observed and its size was increasing with the driving input power. The initial hot spot with an anisotropic–isotropic transition of 29 °C appeared near the cathode region under the drive voltage of 2.95 V and the current of 8.1 mA. The size of the hot spot was increased with input power. Micro thermocouple was embedded into the epoxy package for the investigation of its size effects on thermal behavior. For the specific structure of LED package investigated the thermal resistances were calculated to be 265 °C/W and 215 °C/W for the low epoxy domed package and high epoxy domed package, respectively. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this article, the magnetic properties of Na-oleate coated and uncoated iron oxide nanoparticles were investigated by Electron Paramagnetic Resonance (EPR) technique.
Abstract: Superparamagnetic iron oxide nanoparticles were prepared by the co-precipitation technique. Then, fine iron oxide nanoparticles were coated by Na-oleate. Magnetic properties of Na-oleate coated and uncoated iron oxide nanoparticles were investigated by Electron Paramagnetic Resonance (EPR) technique. At room temperature, a single, strong and broad EPR signal was observed for both samples with effective g-values of 2,0839 and 2,18838 for coated and uncoated samples, respectively. The intensity, line width and the resonance field for both coated and uncoated samples are strongly temperature dependent. When the sample is coated with Na-oleate, the line width and the resonance field values of the EPR signal increase due to the decrease in the magnetic interaction between the particles. The total effective magnetic moment of such coated particles is found to decrease, which is most likely due to a non-collinear spin structure originated from the pinning of the surface spins and coated surfactant at the interface of nanoparticles.
TL;DR: In this article, a superparamagnetic colloid with dextran molecules of different molecular weights was synthesized and characterized by magnetometry and Nuclear Magnetic Relaxation Dispersion (NMRD) profiles, which gave the evolution of the water protons with the external magnetic field.
Abstract: Proton relaxation in superparamagnetic colloids is influenced by the structure of the coating surrounding the ferrimagnetic nanocrystals. Colloidal suspension of superparamagnetic crystals of the same size, but coated with dextran molecules of different molecular weights, were synthesized and characterized by magnetometry and Nuclear Magnetic Relaxation Dispersion (NMRD) profiles, which give the evolution of the water protons with the external magnetic field. The evolution of these NMRD curves with the length of the coating molecule (respectively 35000, 71000 and 200000 g.mol–1) is characterized by an increase of relaxivity at low field. This evolution can be explained by a change of the magnetic anisotropy due to the dipolar coupling between neighbouring superparamagnetic crystals in the particle. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this article, the Ramaman spectra of lead chalcogenides (PbTe, PbSe and PbS) were studied at room temperature and ambient pressure.
Abstract: Raman spectra of single crystals of lead chalcogenides (PbTe, PbSe, PbS) were studied at room temperature and ambient pressure. The structure of spectra for all compounds is rather similar showing the bands in one- and two-phonon range. Possible spectra identification is discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, the defect types responsible for emission peaks observed in the band-edge emission region were classified into three groups: oxygen vacancies, interstitial zinc, and residual aluminum impurities.
Abstract: We have studied photoluminescence spectra in the band-edge emission region of very high quality undoped ZnO, as a function of both (i) sample growth methods and conditions, and (ii) measurement temperatures. As a result, we have classified the defect types responsible for emission peaks observed in the band-edge emission region into three groups. In addition, probable lattice defects responsible for some of the emission peaks are suggested to be (i) oxygen vacancies and/or interstitial zinc, and (ii) residual aluminum impurities. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, the structural, optical, and electronic properties of polycrystalline SiGe films have been determined by a variety of techniques and for different Ge contents, and the use of such films in thin-film solar cells is discussed.
Abstract: Recent results concerning the aluminium-induced crystallization of thin SiGe alloy films are reviewed. This crystallization process can be employed throughout the entire alloy range and results in polycrystalline material without a significant amount of phase separation. The structural, optical, and electronic properties of the polycrystalline SiGe films have been determined by a variety of techniques and for different Ge contents. The use of such films in thin film solar cells is discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, the authors have grown Zn1−xCrxTe films by molecular-beam-epitaxy (MBE) and investigated their magnetic properties with variation of Cr concentrations (x) between 0.01-0.08.
Abstract: We have grown Zn1−xCrxTe films by molecular-beam-epitaxy (MBE) and investigated their magnetic properties with variation of Cr concentrations (x) between 0.01–0.08. Systematic increase of the lattice constant was observed by XRD only up to around x = 0.02. Measurements of the magnetizations M–H reveal that ferromagnetic transition occurs in the films at low temperatures. The transition temperature (TC) which was estimated from Arrott-plots increased with Cr concentration up to about 100 K for x = 0.08. However, the temperature dependence of the magnetization M-T shows different curves below TC for field-cooled (FC) and zero-field-cooled (ZFC) processes. Moreover, their paramagnetic Curie temperatures (Θ), estimated from the higher temperature M-T curves, are different from and much higher than TC. These behaviours could be attributed to the superparamagnetism in the films. Indeed, many defects such as stacking faults are observed in the sample with x = 0.08 through HRTEM. It could give rise to the distribution of the Cr concentrations and/or the presence of precipitates including Cr. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, the characterization of bulk and epitaxial ZnO films doped by nitrogen was reported and the optical properties were investigated by steady state and time resolved photoluminescence (PL).
Abstract: We report on the characterization of bulk and epitaxial ZnO films doped by nitrogen. The ZnO thin films were grown on GaN templates and on ZnO single crystals by vapor phase deposition using Zn and NO2/N2O as precursors. Nitrogen was introduced in the epitaxial films by a mixture of ammonia in the total N2 flow and by ion implantation into the bulk crystals. The optical properties were investigated by steady state and time resolved photoluminescence (PL). We observed a well structured donor–acceptor-pair (DAP) band with a zero phonon line (ZPL) at 3.235 eV. Time resolved PL measurements allowed to conclude on the compensation. Diffusion of Ga from the GaN templates into the ZnO layers was detected by SIMS. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, the optical and structural properties of a series of ZnO1−xSx films deposited by radiofrequency sputtering on float glass and sapphire substrates were investigated.
Abstract: We report on the optical and structural properties of a series of ZnO1−xSx films deposited by radio-frequency sputtering on float glass and sapphire substrates. In the range 0 < x < 0.4 we find that the films have wurtzite symmetry and the lattice constant varies linearly on the composition as confirmed by photoelectron spectroscopy and Rutherford backscattering. Raman measurements show that the spectral position of the A1(LO) mode is sensitive to the sulfur content in the films. The composition dependence of the band gap was evaluated by analyzing the absorption coefficient as a function of the square root of the photon energy (direct transition). The energy gap shifted by more than 500 meV to lower energies indicating a bowing of appr. 2.5 eV in contrast to previous predictions. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
TL;DR: In this paper, the results obtained on spin-dependent processes via electrically detected magnetic resonance (EDMR), capacitance-detected magnetic resonance, and noise-detection magnetic resonance are reviewed.
Abstract: The results obtained on spin-dependent processes via electrically detected magnetic resonance (EDMR), capacitance-detected magnetic resonance (CDMR) and noise-detected magnetic resonance (NDMR) in a variety of different semiconductor materials, devices and nanostructures are reviewed. Similar to optically detected magnetic resonance (ODMR), these detection methods are significantly more sensitive for the detection of paramagnetic states and defects than conventional electron spin resonance (ESR) and can be applied also to semiconductors with an indirect band gap. Using GaAs/AlGaAs-heterostructures and thin films of amorphous hydrogenated silicon (a-Si:H) as examples, the physics of spin-dependent recombination and its detection via spin-dependent photoconductivity is briefly recapitulated. EDMR on pn-diodes from GaP, GaAsP and group-III nitrides, resonant spin–spin scattering in strained Si/SiGe heterostructures, new hysteresis effects in the longitudinal magneto-transport through two-dimensional electron gases and edge-magneto plasmons in different III–V heterostructures are discussed. Various aspects of ferromagnetic III–V semiconductors are investigated, including doping of GaN with Mn, inhomogeneous magnetization of GaMnAs and control of ferromagnetism in semiconductors via hydrogen. Finally, preliminary EDMR experiments on the detection of single paramagnetic defects in MOSFETs via random telegraph noise are presented. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)