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The simultaneous removal of organic and inorganic pollutants from wastewater is a complex challenge and requires usually several sequential processes. Here, we demonstrate the fabrication of a hybrid material that can fulfill both tasks: (i) the adsorption of metal ions due to the negative surface charge, and (ii) photocatalytic decomposition of organic compounds. The bioinorganic hybrid membrane consists of cellulose fibers to ensure mechanical stability and of Bi4O5Br2/BiOBr nanosheets. The composite is synthesized at low temperature of 115 °C directly on the cellulose membrane (CM) in order to maintain the carboxylic and hydroxyl groups on the surface that are responsible for the adsorption of metal ions. The composite can adsorb both Co(II) and Ni(II) ions and the kinetic study confirmed a good agreement of experimental data with the pseudo-second-order equation kinetic model. CM/Bi4O5Br2/BiOBr showed higher affinity to Co(II) ions than to Ni(II) ions from diluted aqueous solutions. The bioinorganic composite demonstrates a synergistic effect in the photocatalytic degradation of rhodamine B (RhB) by exceeding the removal efficiency of single components. The fabrication of the biologic-inorganic interface was confirmed by various analytical techniques including scanning electron microscopy (SEM), scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM EDX) mapping, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The presented approach for controlled formation of the bioinorganic interface between natural material (cellulose) and nanoscopic inorganic materials of tailored morphology (Bi–O–Br system) enables the significant enhancement of materials functionality.

International audience; The band alignment, interface states, interface coupling, and carrier transport of semiconductor heterojunctions (SHs) need to be well understood for the design and fabrication of various important semiconductor structures and devices. Scanning tunneling microscopy (STM) with high spatial resolution and scanning tunneling spectroscopy (STS) with high energy resolution are significantly contributing to the understanding on the important properties of SHs. In this work, the recent progress on the use of STM and STS to study lateral, vertical and bulk SHs is reviewed. The spatial structures of SHs with atomically flat surface have been examined with STM. The electronic band structures (e. g., the band offset, interface state, and space charge region) of SHs are measured with STS. Combined with the spatial structures and the tunneling spectra features, the mechanism for the carrier transport in the SH may be proposed. © 2021 Wiley-VCH GmbH

Alloying of Ge with other group-IV elements – C, Sn or Pb – represents a promising route to realise direct-gap group-IV semiconductors for applications in Si-compatible devices, including light-emitting diodes and lasers, as well as tunnelling field-effect transistors and multi-junction solar cells. To develop a quantitative understanding of the properties and potential of group-IV alloys, we have established a multi-scale simulation framework to enable predictive analysis of their structural and electronic properties. We provide an overview of these simulation capabilities, and describe previously overlooked fundamental aspects of the electronic structure evolution and indirect- to direct-gap transition in (Si)Ge 1–x (C, Sn, Pb) x alloys. We further describe ongoing work related to exploiting this simulation platform to compute the optical and transport properties of (Si)Ge 1–x Sn x alloys and heterostructures.

Semiconductor heterostructures are suitable for the design and fabrication of terahertz (THz) plasmonic devices, due to their matching carrier densities. The classical dispersion relations in the current literature are derived for metal plasmonic materials, such as gold and silver, for which a homogeneous dielectric function is valid. Penetration of the electric fields into semiconductors induces locally varying charge densities and a spatially varying dielectric function is expected. While such an occurrence renders tunable THz plasmonics a possibility, it is crucial to understand the conditions under which propagating resonant conditions for the carriers occur, upon incidence of an electromagnetic radiation. In this manuscript, we derive a dispersion relation for a p&ndash, n heterojunction and apply the methodology to a GaAs p&ndash, n junction, a material of interest for optoelectronic devices. Considering symmetrically doped p- and n-type regions with equal width, the effect of certain parameters (such as doping and voltage bias) on the dispersion curve of the p&ndash, n heterojunction were investigated. Keeping in sight the different effective masses and mobilities of the carriers, we were able to obtain the conditions that yield identical dielectric functions for the p- and n-regions. Our results indicated that the p&ndash, n GaAs system can sustain propagating resonances and can be used as a layered plasmonic waveguide. The conditions under which this is feasible fall in the frequency region between the transverse optical phonon resonance of GaAs and the traditional cut-off frequency of the diode waveguide. In addition, our results indicated when the excitation was slightly above the phonon resonance frequency, the plasmon propagation attained low-loss characteristics. We also showed that the existence or nonexistence of the depletion zone between the p- and n- interfaces allowed certain plasmon modes to propagate, while others decayed rapidly, pointing out the possibility for a design of selective filters.

Different source field plate (FP) connections are compared for the all-GaN integrated cascode device to address the capacitance matching and turn-off controllability issues reported in the conventional GaN plus Si cascode. The experimental results suggest that the cascode device with an FP connected to the source terminal can significantly suppress the off-state internode voltage, leading to minimized capacitive energy loss and reduced overvoltage stress at the internode. This is attributed to the reduced ratio of the drain-source capacitance of the depletion mode cascode part to the total capacitance at the cascode internode. An additional FP on the E-mode cascode part is proposed to further suppress the off-state internode voltage and benefit the device. Cascode devices with the source FP connecting to the enhancement mode gate have an improved switching controllability via gate resistance during turn-off and hence enhanced dv/dt immunity in the drain loop.

Near-infrared nanowire lasers are promising as ultrasmall, low-consumption light emitters in on-chip optical communications and computing systems. Here, we report on a room-temperature near-infrared nanolaser based on an AlGaAs/GaAs nanowire/single-quantum-well heterostructure grown by Au-catalyzed metal organic chemical vapor deposition. When subjects to pulsed optical excitation, the nanowire exhibits lasing, with a low threshold of 600 W/cm2, a narrow linewidth of 0.39 nm, and a high Q factor of 2000 at low temperature. Lasing is observed up to 300 K, with an ultrasmall temperature dependent wavelength shift of 0.045 nm/K. This work paves the way towards ultrasmall, low-consumption, and high-temperature-stability near-infrared nanolasers.

International audience; In this work, Molecular Beam Epitaxy (MBE) grown tunnel junctions (TJs) based on GaAs(Sb)(In) materials are experimentally and numerically studied. From simple GaAs TJs grown with various n-doping levels, we develop a semi-classical interband tunneling model able to quantify the magnitude of the tunneling current density, which shows that direct interband tunneling is the predominant tunneling mechanism in GaAs tunnel junctions instead of trap-assisted-tunneling mechanisms. Numerical simulations based on non equilibrium perturbation theory through Non Equilibrium Green's Functions (NEGF) and a multi-band kp hamiltonian that includes both gamma and L valleys were performed by the IM2NP (Marseille) and confirmed this result. In order to further improve the performance of the TJs, we are fabricating a type II tunnel heterojunction based on GaAsSb and InGaAs materials.

The key challenge for nanoelectronics technologies is to identify the designs that work on molecular length scales, provide reduced power consumption relative to classical field effect transistors (FETs), and that can be readily integrated at low cost. To this end, a FET is introduced that relies on the quantum effects arising for semimetals patterned with critical dimensions below 5 nm, that intrinsically has lower power requirements due to its better than a “Boltzmann tyranny” limited subthreshold swing (SS) relative to classical field effect devices, eliminates the need to form heterojunctions, and mitigates against the requirement for abrupt doping profiles in the formation of nanowire tunnel FETs. This is achieved through using a nanowire comprised of a single semimetal material while providing the equivalent of a heterojunction structure based on shape engineering to avail of the quantum confinement induced semimetal-to-semiconductor transition. Ab initio calculations combined with a non-equilibrium Green's function formalism for charge transport reveals tunneling behavior in the OFF state and a resonant conduction mechanism for the ON state. A common limitation to tunnel FET (TFET) designs is related to a low current in the ON state. A discussion relating to the semimetal FET design to overcome this limitation while providing less than 60 meV/dec SS at room temperature is provided.

Au-catalyzed InxGa1-xAs nanowires (NWs) and InxGa1-xAs/GaAs core-shell NWs were grown by molecular beam epitaxy on (1 1 1)B GaAs. The effects of In content, growth temperature, and V/III elemental flux ratios on NW morphology have been investigated. The structure of the NWs has been characterized by SEM and transmission electron microscopy and their optical properties by low-temperature photoluminescence.

In this work the choice of appropriate test structures and characterization methods for recessed Ohmic contacts to AlGaN/GaN is discussed. It is shown that, in the worst-case scenario, the prevailing assumption of identical sheet resistance between and under the contacts can lead to errors of up to 3000 % in the extracted specific contact resistance.

International audience; Electronic properties of the Al0.56In0.44Sb/Ga0.5In0.5Sb heterostructure grown by molecular beam epitaxy are investigated. We measure by means of x-ray photoemission spectroscopy, photoluminescence, and Hall effect measurements the key parameters involved in the achievement of a high speed and very low power consumption field effect transistor: conduction and valence band offsets, energy gaps of channel and barrier materials, electron effective mass, and density of states in the channel. We observe the influence of the quantum well thickness on the electron Hall mobility and sheet carrier density. A type I heterostructure exhibiting a room temperature electron mobility of 25 000 cm2 V-1 s-1 with a sheet carrier density of 1.5×1012 cm-2 is demonstrated for the widest channel. We show that the thickness of the channel influences both Hall density and mobility through a multisubband occupancy. We discuss about the scattering mechanisms limiting the mobility in the second subband.

X-ray standing waves measurements have been performed on a set of six InAsP/InP superlattices exhibiting a wide range of lattice strain values and on both the (002) and (004) reflections. The objective was to assess the XSW technique as a structural probe in superlattices. For samples with perpendicular lattice misfit less than 1.5% we fmd clear XSW modulations in the As fluorescence ; this signal is well reproduced by simulations performed by solving the Takagi-Taupin equations. For samples with higher misfit a negligible XSW signal is found, indicating considerable lattice disorder.

Time-resolved photoreflectance (PR) in AlInN/GaN heterostructures was applied to study carrier dynamics at energies extending from the uniform AlInN alloy band gap to the band gap of GaN. PR at the AlInN band gap has been found to have subpicosecond decay. Such ultrafast carrier relaxation from the extended to the sub-band edge states implies that the localization sites are small and dense, most probably originating from the In-rich clusters. At energies below the AlInN band gap, a complicated energy dependence of the PR signal is attributed to the properties of the localized states and to the modulation of the interface electric field by photoexcitation. QC 20130109

We investigated transport properties of organic heterointerfaces formed by single-crystals of two organic donor-acceptor molecules, tetramethyltetraselenafulvalene (TMTSF) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). Whereas the individual crystals have un-measurably high resistance, the interface exhibits a resistivity of few tens of MegaOhm with a temperature dependence characteristic of a small gap semiconductor. We analyze the transport properties based on a simple band-diagram that naturally accounts for our observations in terms of charge transfer between two crystals. Together with the recently discovered tetrathiafulvalene (TTF)-TCNQ interfaces, these results indicate that single-crystal organic heterostructures create new electronic systems with properties relevant to both fundamental and applied fields.

We applied the internal photoemission technique to the direct observation of deep levels together with barrier heights and band discontinuities at different semiconductor heterostructure interfaces. Its performances and capabilities are superior to those of established techniques: the energy resolution is excellent and it can be applied to "real" device interfaces under bias. The technique was successfully tested for the Pd/n-GaAs and Pd/a-Si:H Schottky barriers as well as for the a-Ge/n-GaAs and a-Ge/p-GaP heterojunctions. We found a Pd/n-GaAs Schottky barrier height of 0.78 eV and an a-Ge/n-GaAs valence band discontinuity of 0.42 eV; in both cases the Fermi level was "pinned" at an averaged value of 0.76+/-0.03 eV above the top of the GaAs valence band. Furthermore we directly measured a feature at 1.09 eV, due to Pd-induced empty states approximately 1.1 eV above the valence band. The Pd/n-GaAs Schottky barrier also exhibits a feature at 1.36 eV, explained by transitions from the valence band to a localized state, made possible by the band bending. In the case of a-Ge/n-GaP we found a DELTA-E(V) = 0.88 +/- 0.05 eV and a DELTA-E(C) = 0.68 +/- 0.05 eV. Finally, in the Pd/a-Si:H Schottky barrier, we demonstrated the contribution of resonant tunneling through localized states of the conduction band.

We present a highly efficient hybrid heterojunction photovoltaic (PV) cell with a colloidal inorganic nanocrystal (NC) electron donor and an organic electron acceptor. The heterojunction is formed by a thin film of cross-linked PbS NCs and a vacuum deposited C60 layer. Compared to the PbS-only PV cell, the heterojunction device has improved the power conversion efficiency from 1.6% to 2.2% under 1 sun of simulated Air Mass 1.5 Global (AM 1.5G) irradiation. The C60 layer effectively prevents exciton quenching at the NC/metal interface, as evidenced by a significant improvement in fill factor of the heterojunction devices.

We use molecular dynamics (MD) with the reactive interatomic potential ReaxFF to characterize the local strains of epitaxial Si/Ge/Si nanoscale bars as a function of their width and height. While the longitudinal strain (along the bars length) is independent of geometry, surface relaxation leads to transverse strain relaxation in the Ge section. This strain relaxation increases with increasing height of the Ge section and reduction in its width and is complete (i.e., zero transverse strain) for roughly square cross sections of Ge leading to a uniaxial strain state. Such strain state is desirable in some microelectronics applications. From the MD results, which are in excellent agreement with experiments, we derive a simple model to predict lateral strain as a function of geometry for this class of nanobars.

In this paper, we investigate the structural properties of AlGaN/GaN heterostructures grown by metal organic chemical vapor deposition on sapphire substrates with different thicknesses using high-resolution x-ray diffraction and Raman scattering methods. We discuss the microscopic nature of spatial-inhomogeneous deformations and dislocation density in the structures. Microdeformations within mosaic blocks and the sizes of regions of coherent diffraction are determined. We reveal a gradient depth distribution of deformations in the mosaic structure of nitride layers, as well as at the interface regions of the sapphire substrate on the microscale level using confocal micro-Raman spectroscopy. We determine that an increase in substrate thickness leads to a reduction in dislocation density in the layers and an increase in the elastic deformations. The features of the block structure of nitrides layers are shown to have a significant influence on their elastic properties.

Optical properties of the GaSb/GaAs quantum dot system are investigated using a time-resolved photoluminescence technique. In this type-II heterostructure the carriers of different species are spatially separated and, as a consequence, a smooth evolution of both the emission wavelength and decay timescale is observed. A wavelength shift of 170 nm is measured simultaneously with the progressive timescale change from 100 ps to 23 ns. These phenomena are explained by the evolution of the carrier density, which brings a modification to the optical transition probability as well as the shift in the emission toward the higher energies. (C) 2009 American Institute of Physics. (10.1063/1.3202419)

We develop a new three-dimensional multiparticle Monte Carlo ({\it 3DmpMC}) approach in order to study the hopping charge transport in disordered organic molecular media. The approach is applied here to study the charge transport across an energetically disordered organic molecular heterojunction, known to strongly influence the characteristics of the multilayer devices based on thin organic films. The role of energetic disorder and its spatial correlations, known to govern the transport in the bulk, are examined here for the bilayer homopolar system where the heterojunction represents the bottleneck for the transport. We study the effects of disorder on both sides of the heterojunction, the effects of the spatial correlation within each material and among the layers. Most importantly, the {\it 3DmpMC} approach permits us to treat correctly the effects of the Coulomb interaction among carriers in the region where the charge accumulation in the device is particularly important and the Coulomb interaction most pronounced. The Coulomb interaction enhances the current by increasing the electric field at the heterojunction as well as by affecting the thermalization of the carriers in front of the barrier. Our MC simulations are supplemented by the master equation (ME) calculations in order to build a rather comprehensive picture of the hopping transport over the homopolar heterojunction., 26 pages, 11 figures, LaTeX

Deep-level transient spectroscopy (DLTS) has been used to measure the concentration and energy position of deep electronic states in CuInS2. Flat TiO2?CuInS2 heterojunctions as well as TiO2-CuInS2 nanocomposites have been investigated. Subband-gap electronic states in CuInS2 films are mostly due to antisite point defects and vacancies. Substitution of indium with copper, CuInII, leads to an acceptor state 0.15 eV above the valence band, while copper vacancies, VCuI, are acceptor states at 0.1 eV. Furthermore, indium on a copper position, InCu?, yields a donor state at 0.07 eV below the conduction band, while sulphur vacancies are donor states at 0.0 = eV. With DLTS, these states are indeed found. For flat configurations, VCuI are the dominant acceptors with a concentration of 1.83×1017?cm?3. In contrast for nanocomposites CuInII are the dominant acceptors having a concentration of 6.7×1017?cm?3. We conclude that the concentration of antisite defects in nanocomposite CuInS2 is significantly higher than that in flat films of CuInS2.

A waveguide taper design for uncladded rib or channel waveguides on InGaAsP-InP with polarization-independent coupling loss to the fiber is proposed. The spot size variation of the guided mode along the taper is investigated numerically by a two-dimensional finite difference method. By introducing thin guiding layers below the waveguide it is shown that the taper structure can be designed to have relaxed fabrication tolerances and a mode matching loss to the fiber of 1 dB.

Amorphous silicon/crystalline silicon heterojunction solar cells, deposited by the plasma-enhanced chemical vapor deposition (PECVD) technique, have been fabricated using different technologies to passivate defects at the heterointerface: without treatment, the insertion of a thin intrinsic amorphous layer or that of a thin intrinsic epitaxial layer. The open circuit voltage of heterojunction solar cells fabricated including an intrinsic amorphous buffer layer is strangely lower than in devices with no buffer layer. The structure of the amorphous buffer layer is investigated by high resolution transmission electron microscope observations. As an alternative to amorphous silicon, the insertion of a fully epitaxial silicon layer, deposited at low temperature with conventional PECVD technique in a hydrogen-silane gas mixture, was tested. Using the amorphous silicon/crystalline silicon (p a-Si/i epi-Si/n c-Si) heterojunction structure in solar cells, a 13.5% efficiency and a 605-mV open circuit voltage were achieved on flat Czochralski silicon substrates. These results demonstrate that epitaxial silicon can be successfully used to passivate interface defects, allowing for an open circuit voltage gain of more than 50 mV compared to cells with no buffer layer. In this paper, the actual structure of the amorphous silicon buffer layer used in, heterojunction solar cells is discussed. We make the hypothesis that this buffer layer, commonly considered amorphous, is actually epitaxial.

High-resolution x-ray diffraction, in surface symmetric, skew symmetric, and grazing incidence in-plane diffraction geometries, has been used to investigate the effect of an AlN interlayer between micron thick GaN and AlxGa1−xN layers grown by metalorganic vapor phase epitaxy on basal plane sapphire. No change is found in the tilt mosaic (threading screw dislocation density) with thickness or Al fraction x of the upper layer. A linear increase in the twist mosaic (threading edge dislocation density) was observed as a function of interlayer thickness and x. For all samples the twist mosaic of the AlGaN was significantly greater, by at least a factor of two, than that of the GaN layer. With increasing interlayer thickness the in-plane lattice parameter of the AlGaN decreased. The results are explained in terms of extra threading edge dislocations resulting from relaxation at the GaN/AlN interface.

Ga-face AlGaN/GaN heterostructures with different sheet carrier concentrations have been studied by photoluminescence and Raman spectroscopy. Compared to bulk GaN, an energy shift of the excitonic emission lines towards higher energies was observed, indicating the presence of residual compressive strain in the GaN layer. This strain was confirmed by the shift of the E2 Raman line, from which biaxial compressive stresses ranging between 0.34 and 1.7 GPa were deduced. The spontaneous and piezoelectric polarizations for each layer of the heterostructures have been also calculated. The analysis of these quantities clarified the influence of the residual stress on the sheet electron concentration (ns). Possible causes for the discrepancies between the calculated and experimentally determined sheet carrier densities are briefly discussed. Andres.Cantarero@uv.es ; Gema.Martinez@uv.es

The device performance of a novel color sensitive diode (p-i-i-i-n-diode)-based on amorphous silicon is discussed. The detectors are developed with regard to the /spl mu//spl tau/-(carrier mobility/spl times/lifetime)-product and the bandgap of the different i-layers resulting in a voltage controlled spectral response. Since the linear independence of the spectral response curves and a linear response of the photocurrent on the incident light intensity is a prerequisite for the generation of a red-green-blue signal, the influence of light intensity on the color separation is examined by spectral response measurements under different monochromatic bias illumination. Additionally, numerical simulations are carried out to study the optoelectronic properties of these devices. Finally, a deconvolution method is presented which allows the transformation of the measured spectral response curves into a red-green-blue signal.

The detection of the fundamental components of the visible light (blue, green, red) is realized with a multispectral photodiode based on amorphous silicon. The preferential carrier collection region of this two-terminal device shifts upon changing the applied bias voltage, which leads to a color sensitivity. Structures with controlled bandgap and mobility-lifetime product exhibit a dynamic behavior above 95 dB. Three linearly independent spectral response curves can be extracted to generate a RGB-(red-green-blue)-signal. Bias voltage switching experiments under different monochromatic illumination conditions are carried out to investigate the time-dependent behavior. Furthermore, in order to improve the understanding of the photocurrent transients, we have characterized the voltage-dependent capacitance behavior, Thus, a Simulation Program with Integrated Circuit Emphasis (SPICE) model including the capacitance-voltage (CV) data has been developed, which describes the transient behavior of the detector. The simulations are in good agreement with the experimental data and allow an interpretation of the transient photocurrent response after bias voltage switching. Based on these results, optimization criteria to improve the transient behavior are discussed.

In the present paper we discuss the electronic properties of semiconductor heterojunctions, focusing on the band offset problem. We address interface-specific phenomena, where the conditions of growth -- including controlled contamination and strain effects -- may significantly alter the properties of the junction. We study the effects of ultrathin intralayers (i.e., heterovalent implantation) both at homojunctions (such as GaAs/Ge/GaAs) and heterojunctions (such as GaAs/Si/AlAs). In both cases, our theory demonstrates how the intralayers control the band offset: this result is confirmed by recent experimental observation in several systems. We then consider the band-offset engineering at lattice-mismatched heterojunctions, studying the paradigmatic case GaAs/Si. We evaluate the band-offset for several fully relaxed inequivalent interfaces. Both macroscopic strain and microscopic morphology effects are considered.

We present a photoemission study of the initial growth stages of amorphous Si on the InP(110) cleaved surface, performed at 120 K and compared with the room-temperature (RT) results. Deposition at low temperature gives a larger valence-band discontinuity with respect to RT and high-temperature (280-degrees-C) growth. This effect is explained by the smaller outdiffusion of In atoms in the silicon overlayer.

A strong voltage-dependent tunneling anisotropic magnetoresistance (TAMR) effect was observed in a fully epitaxial Co2MnSi/n-GaAs junction and a Co50Fe50/n-GaAs junction. Angular dependence of the tunnel resistance showed uniaxial-type anisotropic tunnel resistance between the [110] and [11ˉ0] directions in the (001) plane. The voltage at which the TAMR effect was suppressed was close to that at which the differential conductance reached a minimum in both samples, suggesting that the strength and/or the sign of the internal electric field at the Co2MnSi/n-GaAs and Co50Fe50/n-GaAs junctions could be related to the voltage-dependent TAMR effect through spin-orbit interaction.

The valence-band offset of a lattice-matched In0.17Al0.83N/GaN heterostructure grown by metal-organic vapor phase epitaxy (MOVPE) was investigated by x-ray photoelectron spectroscopy (XPS). Atomic force microscopy and angle-resolved XPS indicated that a thin In0.17Al0.83N (2.5 nm) layer was successfully grown by MOVPE on GaN. The XPS result showed that the valence band offset was 0.2 ± 0.3 eV. This result indicates that the conduction-band offset at the In0.17Al0.83N/GaN interface is large, i.e., 0.9 to 1.0 eV, and occupies a large part of the entire band discontinuity.

A wafer-bonded Ge/Si heterojunction was observed using transmission electron microscopy to analyze its crystallographic properties and to reveal atomic profiles at the interface by energy dispersive x-ray spectroscopy. There was a 2 nm thick transition layer at the heterojunction, where an aligned lattice image from Si to Ge together with a disordered lattice image could be observed. In the Si layer close to the interface, islandlike modified regions were observed to exist, where a large amount of Ge was detected. Oxygen was also detected accumulated at the interface.

A hetero p/n junction diode was fabricated by laminating an amorphous n-type InGaZn5O8 layer to a p-type LaCuOSe film epitaxially grown on a MgO (001) substrate. It exhibited a relatively sharp blue electroluminescence (EL) that peaked at ~430 nm at room temperature when a forward bias voltage above 8 V was applied. The wavelength and bandwidth of the EL band agreed well with those of the excitonic photoluminescence band in LaCuOSe, which indicates that the EL band originates from the exciton in LaCuOSe. This experiment strongly suggests that layered compounds, LnCuOCh (Ln=lanthanide, Ch=chalcogen), are promising as the light-emitting layer in optoelectronic devices that operate in the blue–ultraviolet region.

We have applied an electrochemical capacitance/voltage method to determine doping profiles and material quality of n -type AlxGa1−xAs:Si heterostructures with x ranging from 0.24 to 0.86 in a single measurement step. It was found that the etching rate of the high content Al samples is low and the resulting surfaces are rough, independent of the etchant used. Though surface roughing is associated with an inherent property of AlxGa1−xAs, the doping depth profile can be determined in an accurate way. On the basis of secondary ion mass spectroscopy, Hall effect, and electrochemical capacitance/voltage measurements the total donor concentration could be estimated.