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Showing papers in "Physica Status Solidi (a) in 2003"


Journal ArticleDOI
TL;DR: In this article, the authors investigated the release of Si(OH) 4 from porous Si films under physiological conditions with the aim of developing a bioavailable form of Si, which is vital for normal bone and connective tissue homeostasis.
Abstract: Silicon (Si) in the form of orthosilicic acid (Si(OH) 4 ) is vital for normal bone and connective tissue homeostasis. Porous Si films release Si(OH) 4 in aqueous solutions in the physiological pH range. This study investigates the release of Si(OH) 4 from porous Si films under physiological conditions with the aim of developing a bioavailable form of Si. Using a standardised technique, porous Si films released increasing Si with time. Dissolution was significant at pH 7 and above, and at a temperature of 37 °C. Higher porosity generally promoted dissolution, however multiple layer films did not show enhanced solubility over corresponding single layer controls. These properties will be used to optimise Si nanostructures that slowly deliver orthosilicic acid in the digestive tract.

223 citations


Journal ArticleDOI
TL;DR: In this article, an in situ method for the determination of the stress in GaN layers on hetero-substrates, in particular Si, via measuring the wafer curvature is presented.
Abstract: We present an in situ method for the determination of the stress in GaN layers on hetero-substrates, in particular Si, via measuring the wafer curvature. For device application it is essential to obtain stress free low-curvature layers. With our in situ method we directly observe the evolution of strain and can identify the sources of strain and the efficiency of strain compensating layers. We find a strong increase in tensile stress with increasing Si doping up to 0.18 GPa for a 1018 cm−3 Si doping concentration. This can be significantly reduced by an appropriate buffer layer growth scheme. The compensation of tensile thermal stress by introducing AlN interlayers to avoid cracking of GaN on Si is in situ investigated. We find that the impact of undoped AlN interlayers is independent of growth temperatures Tgrowth up to Tgrowth > 1000 °C. A linear dependence of strain reduction on AlN interlayer thickness up to a thickness of 12 nm is observed. Using appropriate growth schemes more than 6 μm thick crack free high quality GaN layers on Si were grown. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

154 citations


Journal ArticleDOI
TL;DR: In this paper, the acceptor-bound exciton emission at (3.3570 ± 0.0002) eV, assigned in the literature as an acceptor bound exciton, may involve N o complexes.
Abstract: Hall-effect, photoluminescence (PL), and electron paramagnetic resonance (EPR) measurements have been performed in single-crystal ZnO samples annealed in air at 25, 550, 750, and 950 °C, for 30 min each. A 37 meV donor is dominant in the unannealed sample, but nearly disappears during the higher temperature anneals, and is replaced by a 67 meV donor. The 37 meV donor is responsible for a donor-bound-exciton PL line at (3.3631 ± 0.0002) eV, which is dominant in the unannealed sample. The EPR measurements show that N o centers appear in the 750 °C and 950 °C anneals, and they are probably responsible for an increase in the acceptor concentration found from the Hall-effect results. A PL emission at (3.3570 ± 0.0002) eV, assigned in the literature as an acceptor-bound exciton, may involve N o complexes.

140 citations


Journal ArticleDOI
TL;DR: In this article, the authors review recent advances in the development of novel lasing nanocrystalline ceramics, as well as nonlinear and nonlinear-laser crystals, including organics, for χ(2) and χ (3) frequency converters.
Abstract: After a brief examination of known insulating laser crystals and the stimulated emission channels of their generating activator ions, this article reviews recent advances in the development of novel lasing nanocrystalline ceramics, as well as nonlinear and nonlinear-laser crystals, including organics, for χ(2) and χ(3) frequency converters. Several new attractive technologies in the physics and techniques of crystalline lasers are also discussed. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

126 citations


Journal ArticleDOI
TL;DR: In this paper, the real part of the dielectric constant e′ and the ac electrical conductivity σac were measured and the Dielectric loss tangent tan δ was calculated in the frequency range 50-105 Hz and from room temperature up to ≅800 K.
Abstract: Samples with the chemical formula Cu0.5Zn0.5Fe2−xRxO4 (R = La, Nd, Sm and Gd; x = 0 and 0.1) were prepared by the standard ceramic method. The real part of the dielectric constant e′ and the ac electrical conductivity σac are measured and the dielectric loss tangent tan δ is calculated in the frequency range 50–105 Hz and from room temperature up to ≅800 K. e′ and tan δ are found to decrease with increasing the frequency while σac is generally increased. On the contrary e′, σac and tan δ are increased with temperature. No relaxation was detected in tan δ(f) in the investigated frequency range while tan δ(T) showed two maxima. The composition dependence of the dielectric parameters is discussed and the results are explained using Koops's model. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

118 citations


Journal ArticleDOI
TL;DR: In this paper, the concept of photonic crystal waveguides and related device applications in integrated optics are discussed, as well as some of the fabrication technology required to realise these structures in practise.
Abstract: The concept of photonic crystal waveguides and related device applications in integrated optics are discussed, as well as some of the fabrication technology required to realise these structures in practise. Photonic crystal waveguides interact with light on a wavelength scale, which leads to a novel class of miniaturised devices that display designer dispersion.

115 citations


Journal ArticleDOI
TL;DR: In this paper, the authors found that the grain size of V2O5 thin films produced by pulsed laser ablation strongly influences their optical properties, and that the decrease in the optical band gap associated with a change in spectral transmittance of the pulsed-laser-depletion-deposited VO5 films are mainly due to structure evolution from amorphous to crystalline state and size evolution and distribution characteristics of the grains as a function of increasing growth temperature.
Abstract: We found that the grain size of V2O5 thin films produced by pulsed laser ablation strongly influences their optical characteristics. The decrease in the optical band gap associated with a change in spectral transmittance of the pulsed laser deposited V2O5 films are mainly due to structure evolution from amorphous to crystalline state and size evolution and distribution characteristics of the grains as a function of increasing growth temperature. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

114 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of thickness on the net dielectric constant was studied in detail, and it was found that the relaxation times decrease with increasing measuring temperatures, suggesting that the net relaxation phenomenon is associated with the charge carrier transport mechanism.
Abstract: Cd0.6Zn0.4Te thin films of different thicknesses were prepared by the thermal evaporation technique onto well-cleaned Corning glass substrates. The dielectric properties of Al/Cd0.6Zn0.4Te/Al sandwich structures were studied in the frequency range 50 Hz–4 MHz and in the temperature range 300–420 K. The effect of thickness on the net dielectric constant was studied in detail. The bulk dielectric constant was calculated as 13.5, which is consistent with the value of 11.5–8.2 measured at 1 MHz for the films of different thickness varying between 120 and 850 nm. The relaxation phenomenon present in the films is due to the presence of grains and grain boundaries across the film thickness. The relaxation times decrease with increasing measuring temperatures, suggesting that the net relaxation phenomenon is associated with the charge carrier transport mechanism. The grain boundary activation energies, calculated from the spectroscopic plot, vary between 0.61 and 0.53 eV. The variation of conductivity as a function of temperature and frequency reveals non-adiabatic hopping of charge carriers between impurity sites/localized states and the activation energies are found to vary between 0.28 and 0.11 eV. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

106 citations


Journal ArticleDOI
TL;DR: In this article, the activation energy of the carrier was 0.51 eV and room temperature resistivity was determined to be 2 × 109 Ω cm at room temperature by linear fitting and extrapolation to room temperature.
Abstract: Semi-insulating freestanding GaN substrates were produced by hydride vapor phase epitaxy using intentionally introduced iron impurity atoms to compensate residual donors in GaN. Variable temperature resistivity measurements determined the resistivity of an iron-doped GaN sample to be ∼3 × 105 Ω cm at 250 °C. The activation energy of the carrier was 0.51 eV and room temperature resistivity was determined to be ∼2 × 109 Ω cm at room temperature by linear fitting and extrapolation to room temperature. Near-infrared photoluminescence at 1.6 K exhibited sharp emission at 1.3 eV, associated with the 4T1(G) 6A1(S) internal transition of the Fe3+ charge state. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

102 citations


Journal ArticleDOI
TL;DR: In this article, an energy gap of InN < 1 eV and a nonparabolic absorption edge was found for InN 1-x N. The results are critically discussed in the light of recent experiments.
Abstract: We present ab initio calculations of the electronic structure and the optical properties of In x Ga 1-x N. They are completed by studies of the strain influence on the alloys. The results are critically discussed in the light of recent experiments. We find an energy gap of InN < 1 eV and a nonparabolic absorption edge. The strong variation of the alloy gap with the In molar fraction is described by a composition-dependent bowing parameter. The tendency of spinodal decomposition is suppressed by biaxial strain. Its extent depends on the realization of strain accommodation.

99 citations


Journal ArticleDOI
TL;DR: By combining two experimental techniques, electrochemical impedance spectroscopy (EIS) and the coplanar electrodes-gap configuration, the authors monitored the electronic conductivity in nanoporous Ti0 2 in aqueous solution (pH 2) as a function of the electrode potential.
Abstract: By combining two experimental techniques, electrochemical impedance spectroscopy (EIS) and the coplanar electrodes-gap configuration, we monitored the electronic conductivity in nanoporous Ti0 2 in aqueous solution (pH 2) as a function of the electrode potential. As a result of electron accumulation the conductivity varies over more than eight orders of magnitude up to a maximum σ = 3.7 x 10 -3 Ω -1 cm -1 .

Journal ArticleDOI
TL;DR: In this paper, a comparison of room temperature infrared transmittance, reflectance and visible ellipsometry spectra to temperature-dependent Hall effect and conductivity measurements allows a quantitative determination of optical constants and of transport parameters.
Abstract: At room temperature, the optical, transport and magnetotransport properties of homo-epitaxial MPCVD diamond layers with boron contents in the 2 × 10 20 to 2 x 10 21 cm -3 range are expected to be governed by the characteristics of the boron impurity band. A comparison of room temperature infrared transmittance, reflectance and visible ellipsometry spectra to temperature-dependent Hall effect and conductivity measurements allows a quantitative determination of optical constants and of transport parameters. The results are discussed in reference to the metallic-insulator transition in heavily doped semiconductors. This description enables us to discuss the Raman spectra of p + monocrystalline diamond, focussing on the polarization dependence of the low energy tail, of the unassigned broad peak observed around 500 cm -1 and of the optical phonon frequency range where the Fano interference occurs. On the basis of the observed scattering selection rules, we propose that these features result from electronic scattering in the impurity band and from the electron-phonon coupling on the boron center.

Journal ArticleDOI
TL;DR: In this article, the temperature-dependent photoluminescence spectra of highly uniform self-assembled InAs quantum dots (QDs) embedded in In 0.15 Ga 0.8 As/GaAs multi-quantum well (MQW) structures have been investigated.
Abstract: The temperature-dependent photoluminescence (PL) spectra of highly uniform self-assembled InAs quantum dots (QDs) embedded in In 0.15 Ga 0.8 As/GaAs multi-quantum well (MQW) structures have been investigated. Spectral peak shift and PL temperature quenching for ground state (GS) and first excited state (1ES) optical transitions in the range 12-220 K are analyzed. Small FWHM values equal to 37 and 27 meV at 12 K characterize the GS and 1ES transitions, respectively. For the highly uniform QDs no unusual decrease of the FWHM at low temperatures was seen that would be connected with the redistribution of carriers between the QDs. The activation energies of the PL temperature quenching processes for GS and 1ES in InAs QDs are found to be the same, about 50-52 meV. The reasons for the same GS and 1ES thermal activation energies in InAs self-assembled QDs are discussed.


Journal ArticleDOI
TL;DR: In this article, the authors reviewed the recent progress of nitride-based light-emitting diodes (LEDs) and discussed the relation between dislocation density and quantum efficiency.
Abstract: We review the recent progress of nitride-based light-emitting diodes (LEDs) and discuss the relation between dislocation density and quantum efficiency. We also discuss how to improve the external quantum efficiency of nitride-based LEDs. Secondly, the group-III nitride laser diodes (LDs), which emit from near-ultraviolet to pure-blue, are reviewed. Reducing threading dislocations can increase the lifetime of nitride LDs. Using the epitaxial lateral overgrowth technique, a dislocations density of the order of 105 cm−2 has been obtained. The relation between the lifetime of nitride LDs and the density of dislocations is discussed. Finally, near-ultraviolet LDs and pure-blue LDs are described. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Journal ArticleDOI
TL;DR: In this paper, the first diode end-pumped ceramic laser with this novel solid-state material was demonstrated, achieving a 345mW cw output power with the slope efficiency of 26%.
Abstract: We have succeeded in the fabrication of Yb3+ : Y3Al5O12 ceramics by the nanocrystalline technology and a vacuum sintering method. The first diode end-pumped ceramic laser with this novel solid-state material was demonstrated. The 345-mW cw output power was obtained with the slope efficiency of 26%. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Journal ArticleDOI
TL;DR: In this paper, peak profile analysis based on high-resolution X-ray diffractometry and transmission electron microscopy (TEM) was used to measure the distribution of grain sizes, the dislocation density, and the corresponding root mean square strain in ultrafine-grained (UFG) nickel processed by different methods: electrodeposition, equal channel angular pressing (ECAP), cold rolling (CR), high pressure torsion (HPT), and their combinations.
Abstract: Peak profile analysis based on high-resolution X-ray diffractometry and transmission electron microscopy (TEM) were used to measure the distribution of grain sizes, the dislocation density, and the corresponding root mean square strain in ultrafine-grained (UFG) nickel processed by different methods: electrodeposition, equal channel angular pressing (ECAP), cold rolling (CR), high pressure torsion (HPT), and their combinations. The Fourier transforms of the experimental X-ray peak profiles were fitted by theoretical functions calculated on the basis of the model of the microstructure. In this model the crystallites are assumed to have spherical shape and log-normal size distribution. It is also supposed that the strain broadening of the profiles is caused by 〈110〉{111} type dislocations. The results obtained from X-ray diffraction are compared with TEM micrographs. It is found that additional deformation following ECAP further decreases the crystallite size and increases the dislocation density. However, in the electrodeposited specimen the crystallite size is lower and the dislocation density is higher than in the samples obtained by any of the combinations of the severe plastic deformation (SPD) procedures.

Journal ArticleDOI
TL;DR: In this paper, the photoluminescence (PL) mechanism of as-prepared AlN nanowires is discussed. But the PL mechanism is not considered in this paper.
Abstract: AlN nanowires have been successfully prepared via melting Al powder in a NH 3 atmosphere with variable flow rate. The as-prepared nanowires are composed of AlN with diameters of 5 to 40 nm, and lengths of tens of microns. Radian scattering spectra and photoluminescence (PL) of as-prepared AlN nanowires are also investigated. As a result of impurity incorporation and stress, the Raman spectra are shifted to lower frequencies. A blue emission band centered at 434 nm is observed. The PL mechanism of AlN nanowires is discussed.

Journal ArticleDOI
TL;DR: The semi-insulating character of GaN epitaxial layers can be achieved by the control of the early stages of growth on the substrate as mentioned in this paper, where two low temperature (LT) AlN interlayers are added to reduce threading dislocation densities by up to one order of magnitude.
Abstract: The semi-insulating character of GaN epitaxial layers can be achieved by the control of the early stages of growth on the substrate. Adding two low temperature (LT) AlN interlayers is a technique enough powerful to reduce threading dislocation densities by up to one order of magnitude. A compressive strain as high as 2.8 x 10 -3 is induced in the uppermost GaN epilayer. The global structure is kept semi-insulating so that it is a perfect template for undoped AlGaN-GaN HEMTs (High Electron Mobility Transistors). HEMTs with interlayers present better two dimensional electron gas (2DEG) properties: up to 20% higher carrier density (n s ) and 40% higher mobility. Typically n s is as high as 1.7 x 10 13 cm -2 for a record mobility of 1200 cm 2 /Vs. The improvement of the mobility can be correlated to the reduction of nano-scale V-shaped defects in the AlGaN (less morphological-relaxation). The improvement of n s could be explained by the higher piezo-doping resulting from GaN extra-compression and AlGaN weaker relaxation. As a consequence, the DC transistors characteristics are improved: in 2 μm gate transistors, the maximum current and transconductance are increased by up to 80% and 20%, respectively, and could be extrapolated to values as high as 1500 mA/mm and 250 mS/mm for 0.2 μm gate devices.

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate tunable mirrors that consist of a porous silicon microcavity infiltrated with liquid crystal molecules, which can be switched on and off by applying a voltage.
Abstract: We demonstrate tunable mirrors that consist of a porous silicon microcavity infiltrated with liquid crystal molecules. We show theoretically that by utilizing the electro-optic properties of liquid crystals and the sensitivity of the microcavity resonance position to small changes in optical thickness, the porous silicon active mirror can be switched on (high reflectance) and off (low reflectance) by simply applying a voltage. We discuss the issues of obtaining uniform infiltration of liquid crystal molecules in the constricted geometry of the porous silicon microcavity and determining the necessary change in the liquid crystal orientation to achieve a high reflectance contrast. We also present preliminary experimental results showing a greater than 40% change in the reflectance of our active mirror with the application of voltage.

Journal ArticleDOI
TL;DR: In this paper, the sensitivity of the optical reflectivity of porous silicon structures to the refractive index of liquid within the pores is studied for a single layer, a Bragg mirror and a microcavity.
Abstract: The sensitivity of the optical reflectivity of porous silicon structures to the refractive index of liquid within the pores is studied for a single layer, a Bragg mirror and a microcavity. Sucrose solutions of concentration in the range 0.05 to 1.0% by weight are introduced into the pores within a flow cell in order to change the refractive index of the liquid in the pores from 1.3330 to 1.3344. Optimum wavelengths for detection via reflectivity changes are determined based on a signal to noise analysis. The optical thickness of the single layer is also monitored by measuring the fringe spacing via a Fourier transform technique. It is just possible to detect the effect of a change in refractive index of liquid in the pores of 0.00007 for both the reflectivity and optical thickness approaches.

Journal ArticleDOI
TL;DR: In this article, a theory of the fine structure of the excited state of the quantum-dot trion, which is due to spin-spin interactions, is presented, and it is shown that the fine structures are universal for both positive (two holes, one electron) and negative (two electrons, one hole) trions.
Abstract: A theory of the fine structure of the excited state of the quantum-dot trion, which is due to spin-spin interactions, is presented. In particular, it is shown that the fine structure is universal for both positive (two holes, one electron) and negative (two electrons, one hole) trions. It consists of four doublets, three of them forming a compact group of levels separated from the remaining doublet by the energy of the exchange interaction between identical particles (i.e. between two electrons or two holes). The energy separation between the adjacent doublets in the six-level group is of the order of the much smaller energy of the exchange interaction between particles belonging to different bands, i.e. of the exciton exchange energy.

Journal ArticleDOI
TL;DR: In this paper, the effects of source and substrate temperature, ambient gas pressure and the separation between the source and the substrate on the growth rate of CdTe using the close space sublimation (CSS) system have been investigated.
Abstract: The effects of source and substrate temperature, ambient gas pressure and the separation between source and substrate on the growth rate of CdTe using the close space sublimation (CSS) system have been investigated. The growth rate increased as the source temperature increased with an activation energy of 1.9 eV and it was constant and independent of the substrate temperature, up to some breakpoint temperature, above which the rate decreased rapidly to zero. Free sublimation and transport is involved at low pressures such as 7.5 × 10−5 mbar, whereas diffusion-limited transport was involved at pressures of 2 and 6 mbar of N2. The growth rate increased as the separation between the source and the substrate decreased. The film's grain size increased from <1 μm at 335 °C to more than 2.5 μm at above 445 °C. Analysis of the XRD traces indicated that the films grown at 335 °C were a highly preferred (111) orientation and the (111) texture coefficient reduced when the substrate temperature increased. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Journal ArticleDOI
TL;DR: In this article, the dc electrical conductivity of (100−x)Na2B4O7−xWO3 (x = 5, 15, 20 and 30 mol%) glasses is reported in the temperature range 323 −473 K. The density and molar volume for these glasses are consistent with the ionic size, atomic weight and amount of different elements in the glasses.
Abstract: The dc electrical conductivity of (100−x)Na2B4O7−xWO3 (x = 5, 15, 20 and 30 mol%) glasses is reported in the temperature range 323–473 K. The density and molar volume for these glasses are consistent with the ionic size, atomic weight and amount of different elements in the glasses. At high temperatures the Mott model of phonon-assisted small polaron hopping between nearest neighbours is consistent with conductivity data, while at intermediate temperatures the Greaves variable-range hopping model is found to be appropriate. The estimated model parameters such as number of ions per unit volume, hopping distance, polaron radius and activation energy are found to be consistent with the formation of localized states in these glasses. The electrical conduction of these glasses is confirmed to be that of non-adiabatic small polaron hopping. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Journal ArticleDOI
TL;DR: In this paper, the deposition of nickel (Ni) onto a porous silicon (PS) layer by immersion plating from acidic and alkaline fluoride solutions has been studied, and different deposition behaviors are discussed on the basis of mixed potential theory, etching rate of PS and the state of Ni complex formation.
Abstract: The deposition of nickel (Ni) onto a porous silicon (PS) layer by immersion plating from acidic and alkaline fluoride solutions has been studied. In an immersion plating bath of simple hydrofluoric acid (HF) of pH 2 containing Ni ions, no metal deposition was observed. However, visible metallic Ni was deposited from the ammonium fluoride (NH 4 F) alkaline solution of pH 8. The different deposition behaviors are discussed on the basis of mixed potential theory, etching rate of PS and the state of Ni complex formation. The modified PS layers after the immersion plating were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy. Fourier transform infrared spectroscopy and scanning electron microscopy were also performed to investigate the structural changes and characterizations of PS samples after the plating process. A binary PS/Ni nanostructure without Si oxides is successfully achieved from the alkaline bath.

Journal ArticleDOI
TL;DR: In this article, the influence of oxygen flow rate on structure, composition, density, deposition stress and optical properties of the as-deposited tantalum oxide thin films was reported.
Abstract: We report on the influence of oxygen flow rate on structure, composition, density, deposition stress and optical properties of the as-deposited tantalum oxide thin films. The films were prepared by reactive direct current magnetron sputtering. The sputter current and total pressure were kept constant at 300 mA and 0.8 Pa, respectively. We could deposit fully transparent films at a rate of approximatey 6 nm/min. without noticeable substrate warming from the plasma. Grazing angle XRD showed the films to be amorphous at all oxygen flow rates. Simulations to RBS data revealed, within errors, stoichiometric films above 2 sccm oxygen flow. Moreover argon incorporation in the films above 2 sccm oxygen flow was noted. The density was found to steeply decrease upto 2 sccm followed by a very slow linear decrease with oxygen flow as deduced from X-ray reflectometry. The refractive index, the extinction coefficient and the band gap energy were all obtained by optical spectroscopy. A band gap which increased from 4.17 to 4.23 eV with oxygen flow was determined for films in the transparent region. A characteristic of the defects in the film, γ, which is obtained by simulating the optical spectra, was found to decrease from 85 meV at 6 sccm to 60 meV at 15 sccm oxygen flow. There was no significant change in 7 above 15 sccm. On the other hand the refractive index and the extinction coefficient were found to slightly decrease with increasing oxygen flow for the transparent films. Stress data revealed the films to be under some compressive stress upon deposition. The stress decreased with increasing oxygen flow and stabilized at roughly -250 MPa above 6 sccm oxygen flow.

Journal ArticleDOI
TL;DR: In this article, the transient behavior of AlGaN/GaN HEMTs was studied by current DLTS and two hole-trap-like signals were observed, which reflected the changes in the electron population in the surface states of the HEMT access regions.
Abstract: The transient behaviour of AlGaN/GaN HEMTs was studied by current DLTS. One electron trap and two hole-trap-like signals were observed. The electron trap had an activation energy of 0.61 eV, which was similar to the defect level in n-GaN obtained by capacitance DLTS. It has been pointed out that the hole-trap-like signals dit not originate from changes in hole trap population in the channel, but probably reflected the changes in the electron population in the surface states of the HEMT access regions. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Journal ArticleDOI
TL;DR: In this article, the influence of solvent molecules on silicon dissolution using several hydrofluoric acid containing organic electrolytes was investigated. And the consequences of mixing organic and aqueous solutions are discussed.
Abstract: The aim of this work is to explain the influence of the solvent molecules on silicon dissolution using several hydrofluoric acid containing organic electrolytes. The investigations focus on the morphology of the mesopores and macropores and the electrochemical valence of the overall reaction. Some basic properties of the electrolyte (polarity, tendency to form silicon oxide, and the H donor properties) were found to dominate the macropore formation in p-type silicon. For macropore formation the correct balance between the two main dissolution paths (direct silicon dissolution and dissolution via an anodic oxide) is very important. For mesopores in highly doped p- and n-type silicon the direct dissolution is dominant. The consequences of mixing organic and aqueous solutions are discussed.

Journal ArticleDOI
TL;DR: An inexpensive and compact carbon dioxide sensor based on a porous silicon (PS) film modified with 3-amino-1-propanol has been demonstrated in this paper, where optical reflectivity spectra of PS modified layers display shifts in the Fabry-Perot fringes upon adsorption of carbon dioxide.
Abstract: An inexpensive and compact carbon dioxide sensor based on a porous silicon (PS) film modified with 3-amino-1-propanol has been demonstrated. The modifying reaction as well as the interaction of carbon dioxide with the PS amine-terminated surface has been investigated using Fourier Transform Infrared Spectroscopy. Optical reflectivity spectra of PS modified layers display shifts in the Fabry-Perot fringes upon adsorption of carbon dioxide. This shift scales with the CO 2 concentration.

Journal ArticleDOI
TL;DR: In this paper, the effect of γ-ray radiation on transport and noise properties of high electron mobility transistors (HEMTs) with gate lengths in the range from 350 to 150 nm at room temperature was studied.
Abstract: γ-ray radiation effect has been studied on transport and noise properties of high electron mobility transistors (HEMTs) with gate lengths in the range from 350 to 150 nm at room temperature. Current-voltage (I-V) characteristics of the devices demonstrate higher radiation hardness to 60 Co γ-rays up to doses of 10 9 Rad at larger gate lengths. This confirms the very important role of surface passivation for channel transport of the HEMTs. The deviation of the I-V characteristics parameters saturated current, transconductance, channel conductance, and threshold voltage does not exceed 20% at highest radiation dose. The noise spectra of pre-irradiated devices and after γ-irradiation show different frequency dependences corresponding to different fluctuation processes in the HEMTs. The results are confirmed by dynamic current measurements of the channel conductivity.