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WOS: 000456760700070, 30606580, beta-Agonists are illegally consumed in various products such as food and animal and effect the nutrition distribution owing to change of body fat. In addition, they result in acute poisoning and several symptoms such as muscular tremors and nervousness. A new electrochemical approach based on two-dimensional hexagonal boron nitride (2D-hBN) nanosheets decorated functionalized multi-walled carbon nanotubes (f-MWCNTs) was presented for simultaneous determination of beta-agonists such as phenylethanolamine A (PEA), clenbuterol (CLE), ractopamine (RAC) and salbutamol (SAL) in urine samples. X-ray diffraction (XRD) method, Raman spectroscopy, scanning electron microscope (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used characterizations of nanomaterials. After that, 2D-hBN/f-MWCNTs nanocomposite modified glassy carbon electrode (GCE) was prepared for simultaneous determination of beta-agonists. 1.0 x 10(-12)-1.0 x 10(-8) M and 1.0 x 10(-13) M were founded as the linearity range and the detection limit (LOD) for PEA, CLE, RAC and SAL. Finally, the prepared electrochemical sensor was used for urine sample analysis in presence of ascorbic acid (AA) and uric acid (UA).

WOS: 000441400000076, Serotonin (SER) is the important neurotransmitter and its amount in human body can affect the human life. The low level results in anxiety and carcinoid syndrome. Its high level causes crucial toxicity. Molecularly imprinted approach was used in designing a new electrochemical sensor for serotonin (SER) detection in urine samples. The sensor was prepared based on graphene quantum dots (GQDs) incorporated two-dimensional (2D) hexagonal boron nitride (2D-hBN) nanosheets. All nanomaterials' formation and properties were highlighted with scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) method, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). SER imprinted voltammetric sensor was improved in presence of 80.0 mM phenol containing 20.0 mM SER by CV. 1.0 x 10(-12)-1.0 x 10(-8)M and 2.0 x 10(-13)M were founded as the linearity range and the detection limit (LOD). SER imprinted glassy carbon electrode (GCE) was used for urine sample analysis in presence of the other competitor agents such as dopamine (DOP), tryptophan (TRY) and norepinephrine (NOR). The sensor was also investigated for stability and selectivity.

Defect-assisted nonlinear absorption (NLA) and optical limiting (OL) performance of hexagonal boron nitride nanosheets (h-BNNS) in aqueous suspension and in polymethyl methacrylate matrix (PMMA) as nanocomposite films were studied using open-aperture Z-scan method. To evaluate the transmission in open-aperture Z-scan data, a theoretical model accounting one photon absorption (OPA), two photon absorption (TPA), free carrier absorption (FCA) and saturation of each process was considered. Defect-assisted NLA coefficients and saturation intensity thresholds were extracted from the fitting of the experimental results for 532 and 1064 nm pulse wavelengths. Strong defect-assisted NLA response of h-BNNS was observed while NLA at 532 nm was considerably stronger. This is attributed to the excitation of a greater number of defect states over a wider energy range. Our findings showed that h-BNNS/PMMA nanocomposite films feature highly required properties in OL applications and can function in OL applications in a wide spectral range (?200–1064 nm). © 2021 Elsevier B.V.

Stable magnetic state in the transition metal (TM) doped zincblende (ZB) type compounds ( Al 1 − x M x ) Sb and ( Ga 1 − x M x ) As are investigated on the basis of density functional theory, where M is the 3d TM atom namely Ti, V, Cr, Mn, Fe, Co, Ni and x is the fractional concentration of M. The electronic states and magnetic properties are calculated using the first-principles self-consistent Korringa-Kohn-Rostoker (KKR) Green's function method combined with the coherent potential approximation (CPA). Some of the calculated properties of ZB type materials ( Al 1 − x M x ) Sb and ( Ga 1 − x M x ) As exhibit stable ferromagnetic (FM) states relative to a corresponding disorder local moment (DLM) states. The total energy difference between FM and DLM states per unit cell is used to estimate their Curie temperature (TC) within the mean-field approximation. The calculated TC in Mn, and Cr doped cases are found to be above the room temperature (RT), whereas in Ti, and V doped cases TC remain below the RT. In addition, TC increases with doping concentrations in a range of dilute limit (x ≈ 20%) of magnetic atoms. On the other hand, Fe, and Co doped materials exhibit FM instability due to the dominating super-exchange interaction over the FM one.

We present and thoroughly compare band-structures computed with density functional theory, tight-binding, k · p and non-parabolic effective mass models. Parameter sets for the non-parabolic Γ , the L and X valleys and intervalley bandgaps are extracted for bulk InAs, GaAs and InGaAs. We then consider quantum-wells with thickness ranging from 3 nm to 10 nm and the bandgap dependence on film thickness is compared with experiments for In 0.53 Ga 0.47 As quantum-wells. The impact of the band-structure on the drain current of nanoscale MOSFETs is simulated with ballistic transport models, the results provide a rigorous assessment of III–V semiconductor band structure calculation methods and calibrated band parameters for device simulations.

A very important task on the way of improving the technologies of synthesizing highly effective light-emitting diodes on the basis of silicon is theoretical research into the formation of point defect clusters. One method of obtaining silicon with photoluminescent properties is radiation impact. It causes the formation of various defects in its structure, including point and linear defects, their clusters and complexes. In this paper a mathematical model was used to determine the coordinates and velocities of all particles in the system. The model was used for describing point defect formation processes and studying their evolution with time and temperature. The multi-parametrical Tersoff potential was used for the description of interactions between particles. The values of the Tersoff potential were selected by solving the parametric identification problem for silicon. For developing the models we used the system cohesive energy values obtained by an ab initio calculation based on the density functional theory (DFT). The resultant computer model allows MD simulation of silicon crystal structure with point defects and their cluster with possible visualization and animation of simulation results.

This review paper discusses different synthesis methods and characterization techniques of gallium Phosphide for its application in various fields.

This paper is expected at the study of Ga 1-x In x P/GaAs based solar cell. The effects of indium concentration, lattice parameter mismatch and thickness of the SiO 2 insulating layer on the characteristics and efficiency of the Ga 1-x In x P/GaAs structure were investigated. We noticed that for higher indium concentration, the band gap energy decreases considerably. We found that the efficiency reaches 18% in a lattice-matched δ=50A. For a concentration x > 0.48, we have a compressive strain Δa/a > 0 which leads to a higher efficiency. For x=90%, δ=5 nm and a strain equal Δa/a= 3%, we achieved an efficiency of 27%. The results show that light conversion efficiency has considerably boosted by varying insulating strain values.

In this work the structure of ternary GaxIn1−xP nanowires is investigated with respect to the chemical composition and homogeneity. The nanowires were grown by metal–organic vapor-phase epitaxy. For the investigation of ensemble fluctuations on several lateral length scales, X-ray diffraction reciprocal space maps have been analyzed. The data reveal a complicated varying materials composition across the sample and in the nanowires on the order of 20%. The use of modern synchrotron sources, where beam-sizes in the order of several 10μm are available, enables us to investigate compositional gradients along the sample by recording diffraction patterns at different positions. In addition, compositional variations were found also within single nanowires in X-ray energy dispersive spectroscopy measurements.

The photovoltaic characteristics of a type II staggered heterojunction in the GaSb/GaInAsSb/GaAlAsSb system were studied. The dark current and R 0 A product were investigated at different temperatures. The current–voltage characteristics of n -GaSb/ n -GaInAsSb/ p -GaAlAsSb heterostructures were investigated at room temperature in the photovoltaic mode under illumination by light with wavelength of 0.95–1.0 μm and different intensities. A short-circuit current and an open circuit voltage as a function of intensity of incident light in photovoltaic mode were studied.

Using scanning tunneling microscopy, frequency-modulated scanning atomic-force microscopy, electron diffraction, and density functional theory calculations we investigate a structure of the InAs (001) surface displaying c (8 × 2)/(4 × 2) reconstruction at room temperature. It is found that the room temperature data are satisfactorily interpreted based on the model proposed by Kumpf et al. [Phys. Rev. Lett. 86, 3586 (2001)], however, at cryogenic temperatures the model fails since a different structure, characterized by fourfold period along [110] crystallographic direction, partial disorder and instability, is observed. By the present study we find that the structure is described by corrected Kumpf et al. model where most of atomic rows are left as in the original model and only the dominant indium atom rows running along [110] are changed. At room temperature the dominant rows are disordered and rapidly fluctuate thermally while at cryogenic temperatures they convert to chains of indium aggregates and acquire fourfold period. Moreover, frequently observed incomplete occupancy of the dominant indium rows leads to many different local surface structures, reflected by characteristic “features” in scanning tunneling microscopy patterns. We have classified and explained most of these structures.

With this paper we propose a detailed study of the gradual degradation of InGaN-based laser diodes and Light-Emitting Diodes submitted to electro-thermal stress. The two device structures have been processed from the same epitaxial wafer. Our purpose is to compare the behavior of the two devices by means of electro-optical measurements, electroluminescence characterization, and near field emission measurements. We demonstrate that: (i) stress induces a decrease in the optical power and an increase in threshold current; (ii) the two failure modes are strictly linked each other, and correlated to the increase in defect-related current components, indicating a substantial increase in defect density during degradation; (iii) analysis of characteristic temperature and near-field emission measurements do not indicate any strong variation of injection efficiency nor current confinement of the devices.

Bu çalışma, 4-8 Şubat 2010 tarihlerinde İstanbul[Türkiye]'da düzenlenen 2. World Conference on Educational Sciences (WCES-2010)'da bildiri olarak sunulmuştur. The paper describes liquid phase epitaxial growth and characterization of the GaSb- and InAs-related materials for the photodiodes and thermophotovoltaic applications. It was shown that doping of the melt with holmium results in obtaining the high purity GaInAsSb and InAs layers. The passivation with the 1 M Na2S aqueous solution makes it possible to prepare flat growth surfaces of GaSb(1 0 0) and InAs(1 0 0) substrates after annealing. A reproducible technique has been developed for fabrication of the high-efficiency GaInAsSb/GaAlAsSb and InAs/InAsSbP photodiodes with the long-wavelength photosensitivity edge of 2.4 and 3.8 mu m, respectively. Room temperature detectivity in the spectral peak reaches D* = (0.8-1.0) x 10(11) W-1 cm Hz(1/2) for the GaInAsSb/GaAlAsSb photodiodes and D* = (3.0-5.0) x 109 W-1 cm Hz(1/2) for the InAs/InAsSbP devices. We have adapted the technology for thermophotovoltaic cells operating at an emitter temperature of 1000-1700 degrees

The electrical end optical characteristics of a type II double heterojunction (DH) in the GaSb/GaInAsSb/GaAlAsSb system with staggered band alignment were studied. An analysis of the photodiodes performance through the investigation into electrical and optical characteristics was carried out. The dark current mechanisms in the heterostructures were investigated at several temperatures. The experimental results show that at the low temperature region, the tunneling mechanism of the current flow dominates in both forward and reverse biases. At high temperatures region and in the range of voltage from 0.1 V to 1 V, the reverse current was defined by generation of carriers in the depletion region. Have been estimated the temperature coefficient of the shift of the long-wavelength edge of the spectral sensitivity at half-maximum as Delta lambda/Delta T = 1.6 nm/K. Quantum efficiency of 0.6-0.7 for the investigated photodiodes was reached without any antireflection coating. For GaSb/GaInAsSb/GaAlAsSb TPV cells, the internal quantum efficiency of 90% was achieved at wavelengths between 1.2 and 1.6 mu m. (C) 2010 Elsevier B.V. All rights reserved. Russian Foundation for Basic Research (RFBR) (07-02-01359) Russian Foundation of Basic Research (RFBR) (09-08-91224)

The Metal Organic Chemical Vapour Deposition (MOCVD) grown n-type Gallium nitride (GaN) layers on sapphire (0 0 0 1) substrates have been irradiated at low and room temperatures with 40 MeV Li3+ ions at the fluence of 1 × 1013 ions cm−2. Irradiated samples were characterised by using X-ray diffraction (XRD), photoluminescence (PL), Raman spectroscopy and atomic force microscopy (AFM). XRD results show that the formation of Ga2O3 has been observed upon irradiation. This is due to interface mixing of GaN/Al2O3, at both temperatures. Also the GaN (0 0 0 2) peak splits into two at low temperature irradiation. PL measurements show a yellow emission band shift towards blue band side upon irradiation at 77 K. Raman studies indicate that the lattice disorder is high at room temperature irradiation compared to low temperature irradiation. AFM images indicate the increasing surface roughness after ion irradiation at room temperature when compared to pristine GaN and low temperature irradiated GaN. These observations are discussed in detail with the use of complementary techniques.

International audience; We have studied the in situ HCl etching of Si active areas on patterned wafers. After some in situ HCl etching at 20 Torr of Si(1 0 0), we have locally obtained 2 μm long areas with misorientation angles around 4.5° towards (1 1 0). Furthermore, we have evidenced a recess shape transition from convex (T ≤ 865 °C) to concave (T ≥ 895 °C) as the etch temperature increases, with a nearly flat surface with no facets at T = 880 °C. The morphology of the etched structures at a given time, temperature and PHCl/PH2 ratio will be a function of the slope lengths and the pattern dimensions. Different kinds of surfaces (rounded areas, facets) were obtained in 3.5 μm × 3.5 μm Si windows after HCl etching at 850 °C during 300 s, depending on the stress within. Thermal oxidations can indeed be used to increase by 65 MPa up to 110 MPa the compressive stress in those Si windows which are bordered by SiO2 shallow trench isolation. An increase of the misorientation angle from 4.5° up to 6° occurred after the above-mentioned HCl etch when switching from conventional to highly strained Si windows. For the shortest etching times studied here (150 s), a selective etching of 3.5 μm × 3.5 μm Si windows edges is responsible for the misorientation. The etch is then more uniform. Stress gradients might consequently be one of the main misorientation causes. We have also probed the influence of the shallow trench isolation (STI) thickness on the misorientation. A morphological difference before HCl etching has been shown to be responsible for the transition from sloped to rounded areas. A local loading effect may prevail in this case.

A sputter-cleaned indium-rich (2 × 4) InP(0 0 1) surface was investigated by non-contact scanning atomic force microscopy (NCAFM). Atomically-resolved images of the surface exhibit two different patterns. The patterns can be interpreted within the mixed dimer model of (2 × 4) reconstructed InP(0 0 1) surface. It is shown that due to contrast formation mechanism in NCAFM the features resolved are in close correspondence to scanning tunnelling microscopy (STM) data. Due to chemical interaction a P-terminated tip gives the image similar to an empty-state STM image, whereas an In-terminated tip gives the image resembling a filled-state STM one. Moreover, it is shown that due to dipole–dipole interaction, NCAFM can be sensitive to orientation of In-P dimers.

This paper reviews recent efforts by authors’ group to utilize electrochemical processes for formation, processing and gate control of III–V semiconductor nanostructures. Topics include precise photo-anodic and pulsed anodic etching of InP, formation of arrays of 〈0 0 1〉-oriented straight nanopores in n-type (0 0 1)InP by anodization and their possible applications and macroscopic and nanometer-scale metal contact formation on GaAs, InP and GaN by a pulsed in situ electrochemical process, which remarkably reduces Fermi level pinning. All the results indicate that electrochemical processes can achieve unique and important results, which the conventional semiconductor technology cannot realize, anticipating their increased importance in future semiconductor nanotechnology and nanoelectronics.

We present an overview of recent selective photoluminescence (PL) experiments on shallow levels in ZnSe and GaN. Through two electron transitions (TET) and electronic Raman scattering (ERS) investigations on solid phase recrystallized bulk ZnSe doped with Al, Cl and In, the spectroscopic properties of donor impurities are re-examined. It is shown that the donor spectra previously attributed to Al and Cl are in fact due to common residual impurities. The Al-donor excited states are detected up to n = 6 allowing a very accurate determination of its ionization energy. We show that the central cell correction of Al is vanishing leading to a new evaluation of the Rydberg which is discussed in view of the last experimental determinations of the dielectric constant and electron effective mass. The neutral-donor bound-excitons have been studied in n-type wurtzite GaN homoepitaxial layers and heteroepitaxial layers deposited on sapphire or SiC substrates. It is demonstrated that the existence of strain distributions in heterostructures induces original resonant effects on selective photoluminescence spectra allowing to identify the bound exciton excited states on a large domain of tensile and compressive strains and in particular near the A and B valence band crossing. Finally, the donors are investigated by TET and ERS spectroscopy. (C) 2001 Elsevier Science B.V. All rights reserved.

We report on the femtosecond dynamics of coherent Bloch oscillations in GaAs/Al x Ga 1− x As superlattices. In a superlattice with a miniband width equal to the optical phonon energy of GaAs the Bloch frequency can be tuned into resonance with the LO phonon by an applied electric field. We observe a strong coupling between Bloch oscillations and phonons leading to the coherent excitation of optical phonons when both are brought into resonance. This phenomenon is analyzed theoretically on the base of a microscopic Hamiltonian for the electron–phonon interaction in the superlattice. We show that coupled modes are described by a nonlinear pendulum coupled linearly to an oscillator representing the phonons. Under resonance condition the amplitudes of both modes increase and sidebands appear. The theoretical results are compared to the experimental observations.

Quantum dots based on InP/GaInAs quantum wells were realised using epitaxial infill regrowth into a hole array formed in InP by means of e-beam lithography and reactive ion etching. Metal organic molecular beam epitaxy has been applied for selective infill growth. The growth procedure has been elaborated such that the vertical growth rate in predefined holes agrees with coherent growth and edge effects are minimised. Quantum dots formed in holes with a diameter ranging from 60 nm down to 30 nm in combination with a periodicity of 100 nm were studied. The achievement of quantum dots was evidenced by a blue shift of light emission with decreasing the geometrical quantum dot diameter, in qualitative agreement with calculations. Quantitative discrepancies were found because the effective lateral diameter of the quantum dots proved to be smaller than the geometrical value of the etched holes, caused by the lateral growth of the lower InP barrier.

Basic developmental steps are outlined for the application of metal organic molecular beam epitaxy as an epitaxial fabrication process for InP-based integrated photonic circuits. Besides high-quality performance of the individual devices, implementation of Fe-doped semi-insulating layers and selective area deposition of GaInAsP for the whole composition range are of concern. Low-loss semi-insulating waveguides were fabricated for optically interconnecting and electrically isolating different devices at deposition conditions that have proven adequate for selective area growth and, simultaneously, for effective suppression of Fe-movement. Fabricated laser/waveguide butt-joints, a basic building block for any integrated photonic circuit, demonstrate the potential of metal organic molecular beam epitaxy to form practically ideal lateral growth interfaces without compromising on device performance.

The regrowth behaviour of and dopant diffusion in (Ga)In(As)P : Fe layers selectively deposited by metalorganic MBE was assessed. Device quality regrowth and the absence of lateral diffusion and accumulation effects is demonstrated as an essential feature for the fabrication of InP-based optoelectronic devices.

A comprehensive study is presented of the properties of ridge lasers incorporating In 0.5 Ga 0.5 As self-assembled quantum dots grown on (3 1 1)B and (1 0 0) oriented GaAs substrates. Various laser designs are used to optimize the threshold current density J th and the characteristic temperature T 0 . Also, the effect of a thermal annealing of the samples is investigated as a mean of tuning the laser energy emission. Finally, we show an unusual temperature dependence of the laser emission: increasing temperature from 10 to 290 K produces a narrowing of the dot laser mode distribution.

Detection of scintillation light from LSO (Lutetiumoxyorthosilicate) crystals used in positron emission tomography (PET) is traditionally based on photo- multipliers. The proposal is to develop a novel photo- sensor, which is based on vertically integrating an hydrogenated amorphous silicon (a-Si:H) film on a pixel readout chip. The a-Si:H film is deposited with a n-i-p diode structure. The ASIC (Application Specific Integrated Circuit) performs both signal amplification and readout processing. The advantage of such an approach is the extremely compact and low-cost design, together with ultra- low noise signal retrieval. In addition the a-Si:H offers the technological advantage of direct deposition on the wafer thanks to the low deposition temperature. The article presents the results of quantum efficiency measured on different types of a-Si:H photodiodes deposited on glass (DC measurement) and CMOS circuit (AC measurement). Quantum Efficiency (QE) up to 80% has been measured at the wavelength of interest for the optimized photodiodes. © 2007 Elsevier B.V. All rights reserved.

MBE regrowth on MOVPE grown InP and InGaAsP (1.06 μm) layers was found to demand appropriate surface treatment for not sacrificing epitaxial growth performance. Wet chemical etching using a sulphuric acid based solution as well as surface oxidation using UV light/ozone exposure were found to give very satisfactory and basically equivalent results. Particularly with the quaternary material, both methods prove to be destructive in that a non-neglible amount of material is removed from the surface. The removed thickness tends, however, to be smaller with the UV/ozone based process, an advantage, which becomes especially aparent in the presence of lower band gap InGaAs(P) layers which are strongly attacked by the sulphuric acid etchant.

Layer structures comprising InP and InGaAsP were compared when grown using nitrogen versus hydrogen as carrier gas. Under nitrogen a remarkable improvement in layer uniformity in terms of thickness and PL wavelength is obtained for InGaAsP layers over the whole compositional range. This improvement duplicates for the PL wavelength of quantum wells. The selective-area growth behaves differently regarding the excess growth at mesa edges and the wavelength variation in the vicinity of masked areas. The basic laser parameters, especially the threshold current density, of 1.55 mu m bulk- and MQW-laser structures show at least equivalent, if not superior data when grown under nitrogen.

We report observations of dramatic hysteretic switching behavior in nanometer scale pillar arrays. Using a new technique, we fabricate arrays of closely packed pillars 20–50 nm in diameter from a GaAs/AlAs resonant tunneling diode heterostructure. The array resistance switches between two stable states with a current peak to valley ratio of 500 : 1. Scanning tunneling microscope characterization of individual pillars suggests that the pillars trap charge to block the flow of current through the quantum confined states.

We demonstrate that different spatial correlations among remote impurity charges in the GaAs/AlGaAs quantum well lead to different values of (i) the transport-relaxation time, (ii) the single-particle relaxation time, and that (iii) the different width of the integer quantum Hall plateauxs could be achieved. These findings supply qualitatively new information about the important contribution of the non-random arrangement of remote charges to the transport properties of semiconductor heterostructures.

The resonant polaron effect was investigated for cyclotron transitions N-> N + 1 in magnetic field regimes where the Landau levels N = 2 and 3 cross with the level N = 0 plus one bulk longitudinal optical phonon. The experiment is analyzed in the framework of the improved Wigner-Brillouin perturbation theory taking into account band-coupling phenomena, a finite thickness of the inversion layer in the growth direction, and coupling of the cyclotron transitions due to electron-electron interactions. From the cyclotron mass enhancements, a Fröhlich coupling constant alpha = 0.06 to 0.07 was obtained.

The photon drag effect in a two-dimensional electron gas of a GaAs/AlGaAs multi-quantum well system is measured using the ps infrared pulses of the wavelength-tunable free electron laser source FELIX. The temporal response of the sample on a ps timescale has been verified, and the continuous spectral response through the intersubband resonance is investigated for low and high intensities at room temperature and at T = 100 K. An analysis of the lineshape yields information about the momentum relaxation times of the electrons in the ground and excited subbands.

The photon drag effect of a 2D electron gas is measured using the ps infrared pulses of the wavelength-tunable free electron laser source FELIX. The pulsed photon drag response is found to depend critically on the coupling characteristics of the electrical circuit. We therefore developed an impedance and velocity matched photon drag detector. It consists of a GaAs/AlGaAs multi quantum well sample which forms an integral part of a microstrip line. A Ge-prism enables incoupling at the critical total reflection angle. This novel transmission line integrated photon drag detector (TIP-detector) generates signal transients below 10 ps rise and fall times. Its continuous spectral response through the intersubband resonance is investigated at room temperature and atT=100 K. An analysis of the spectral lineshape of the photon drag current response yields information about the momentum relaxation times of the electrons in the ground and excited subbands.

In molecular beam epitaxy (MBE) grown AlInAs/GaInAs single quantum well high electron mobility transistor structures, the use of low growth temperature for layers below the channel to suppress Si movement is mandatory. An optimized growth temperature profile has been elaborated as a prerequisite to reach high carrier concentrations in combination with high mobilities. The impact of an optimum growth temperature profile on device performance is demonstrated in devices with a saturation current of up to 1000 mA/mm.

Spin quantum beats are detected inGa/AsAl x Ga 1−x Asquantum wells in a magnetic field perpendicular to the growth direction by picosecond time-resolved photoluminescence spectroscopy. We directly determine the electron Lande´g factor as a function of well width from 1 to 20 nm with unprecedented accuracy which makes quantitative comparison with theory possible.

Different gain mechanisms are observed in metal-semiconductor-metal (MSM) photodetectors consisting of coplanar Schottky contacts on a high resistivity GaAs sample. I-V curves taken at different frequencies reveal low-frequency gain due to surface charges. Additionally, the time-resolved photocurrent response indicates the presence of high frequency gain, manifesting itself as a 200 ps long tail in the impulse response. We attribute this effect to injection of electrons by tunneling from the cathode into the semiconductor. The electron injection is caused by holes trapped at defects in the vicinity of the contact. We present a theoretical model for the high-frequency gain, which shows good agreement with the experimental data and explains the observed variation of the tail amplitude with excitation density and contact distance.

Molecular beam epitaxy-grown Al(Ga)InAs/GaInAs single quantum well and multiple quantum well structures, comprising ternary and quaternary barriers, were investigated for laser device applications. Barrier materials of excellent lateral uniformity and high optical and crystalline quality, as well as low interface charge densities of the Al(Ga)InSa/GaInAS heterojunctions, were achieved. The influence of buffer configuration and barrier composition on the well emission properties was studied.

We report on MOVPE growth and characterization of InGaAs/In(GaAs)P and InGaAsP/InP/InAlAs multi-quantum-well structures for electro-optic switching devices, which require abrupt compositional and doping interfaces. Strongly coupled InGaAs/InP Wannier superlattices with a large number of periods show excellent photoluminescence quality and surface morphology. In addition, band-filling effects with very low leakage current density are demonstrated by incorporating InAlAs barrier layers into InGaAsP/InP modulation doped electron transfer structures.

Free and bound electrons in bulk GaAs are investigated by cyclotron resonance in the freeze out regime at temperatures below 40 K. A temperature-induced reversal of the relative intensities of the spin split free electron transition 0 → 1 is observed, providing strong evidence for a spin reversal at a temperature of about 25 K. In contrast, no spin reversal is found for the single electron transition 1s → 2p+1 of the shallow donors.

A model is developed describing Zn outdiffusion during epitaxial growth of a double heterostructure bipolar transistor (DHBT) structure. This model is used for the design of the highly p-doped base layer. Experimental results confirm the calculated doping profiles.

Thermal degradation is identified as the origin for a variety of defects in epitaxial layers. The consequences of these defects are more critical than those of dislocations. It turns out that thermal degradation affects the layer quality more than dislocations.

The time-evolution of photo-Hall mobility, muH, during low-temperature illumination with 1.55 eV photons is presented as determined experimentally. At first muH decreases gradually during illumination, dropping almost to zero, and then increases back to high values, reaching an equilibrium value. The same behavior of mu H is predicted from calculations of time-evolutions of free electrons and holes, derived from the time-evolution of independently measured thermoelectric effect signal and photoconductivity. Results are compatible with the model in which the dynamics of trap filling and changes of relative occupancies of traps with different sign are responsible for transient phenomena observed in photoconductivity, Hall mobility and thermoelectric signal during low-temperature, low-intensity illumination (12 References).

The use of a dispersive system based on the Michelson interferometer in photoluminescence spectroscopy (spectral range 0.7–1.8 eV) employs the Fourier transform of the experimental data to obtain the emitted spectrum. The main cause of error in this mathematical treatment is the incorrect calculation of the phase. This paper shows the influence of the phase errors on the spectra interpretation.

InGaAs/InGaAsP MQW SC lasers for 1.55 μm emission wavelength with different numbers of quantum wells have been fabricated using low-pressure MOVPE. Photoluminescence and gain spectra and threshold current densities and the temperature behaviour T 0 of broad area lasers at varying cavity lengths have been investigated.

We present time resolved photoluminescence measurements of GaAs/Al /sub 0.3/Ga/sub 0.7/As quantum dot structures where no wetting layer is connecting the dots. We show that the two-dimensional character of the wetting layer is not relevant in determining the quantum dot capture, in contrast with the conclusions of several models so far presented in the literature.

Enthalpies of substitutional incorporation of dopants in both sublattices of III-V compounds were analysed using Phillips-van Vechten's dielectric two band model. It has been shown that in the case of very large size mismatch between dopant and host atom, the consequent disorder of the crystal potential can be more important factor in dopant incorporation than the valence mismatch. Present calculations support recent experimental results on `antisite' incorporation of Sb in Ga site in GaN (8 References).

The use of a Sn-In-P melt and of InP cover wafers of different orientation to prevent thermal surface decomposition of InP substrates in liquid phase epitaxy has been compared. An almost equivalent protection efficiency was found for the Sn-In-P solution and a (111B) wafer. However, with the melt approach a remarkable increase of residual impurity density was observed particularly at the interface of epitaxial InGaAs layers.

The initial phases of the oxidation of the GaP(1 1 0) cleaved surface have been studied, by photoemission with synchrotron radiation. A first stage in which an increase in band bending occurs and a second stage in which complete saturation of dangling bonds occurs are distinguished. This result accounts for previous surface reflectance data on the same surface. The processes of band bending variation and dangling bond saturation with oxygen exposure are very similar in GaP(1 1 0) and GaAs(1 1 0).