The infrared-optical properties of GaAs/GaN x As 1− x superlattice (SL) heterostructures (0 < x < 3.3%) are studied by variable angle-of-incidence infrared spectroscopic ellipsometry (IRSE) for wavenumbers from 250 cm −1 to 700 cm −1 . The undoped SL structures where grown on top of a 300 nm thick undoped GaAs buffer layer on Te-doped (001) GaAs substrates by metal-organic vapor phase epitaxy (MOVPE). We observe the well-known Berreman-polariton effect within the GaAs LO-phonon region. We further observe a strong polariton-like resonance near the coupled longitudinal-optical plasmon-phonon frequency of the Te-doped substrate at 306 cm −1 . For analysis of the IRSE data we employ the harmonic oscillator dielectric function model and the Drude model for free-carrier response. The additional resonance feature is explained by pseudo surface polariton (PSP) interface modes between the Te-doped GaAs and the undoped GaAs buffer layer / SL film. We find that the PSP modes are extremely sensitive to free-carrier properties within the SL structures, and we obtain a strong increase in free-carrier concentration within the GaNAs SL sublayers with increasing x from analysis of the IRSE data. We further observe the localized vibrational modes of nitrogen at 470 cm −1 in the GaN x As 1− x SL sublayers with a polar strength that increases linearly with x , and which can be used to monitor the nitrogen concentration in GaN x As 1− x .

In this study the boron lattice site location in ternary BxGa1−xAs and BxGa1−xP thin films grown on (001) GaAs and (001) GaP, respectively, using low pressure metal-organic vapour-phase epitaxy (MOVPE) with boron concentrations between x=0.8% and x=3.2% was investigated with RBS and the 10B(α,p)13C nuclear reaction using a 2.3MeV He+ ion beam. For this purpose, the ion beam was aligned with the [001], [011] and [111] axis and the RBS and proton yield from the nuclear reaction compared with random ion incidence. For comparison, theoretical proton yields which assume boron to be located on substitutional lattice sites only were calculated for each sample/axis combination and compared with the experimental yields. The RBS/channeling measurements show a very good crystal quality of the films with χmin being in the range of 3–5% for the [011] axis. The best crystal qualities, i.e. the lowest χmin values and dechanneling rates, are achieved for low boron concentrations. From NRA/channeling it can be deduced that in the BxGa1−xAs films the fraction of interstitial boron is approximately 5% for low boron concentrations of x=1% and 6–10% for concentrations up to x=3.2%, whereas the fraction of interstitial boron is less than 3% in the BxGa1−xP film studied despite a concentration of x=2.0%. This indicates that antisite effects of the boron incorporation are more likely in GaAs compared to GaP.

We report on the gold-based vapor–liquid–solid (VLS) growth of GaAs/(InGa)As/GaAs axial double-heterostructure nanowires using low-pressure metal-organic vapor phase epitaxy (MOVPE). Systematic growth investigations were performed to study the influence of the growth time, the temperature and the V/III ratio on the composition and the extent of the (InGa)As segments. A group-III precursor growth interrupt prior to and after the (InGa)As growth showed the highest solid indium fraction and the strongest composition gradients at the heterojunctions. The experimental results were discussed considering the droplet composition as well as MOVPE and VLS kinetics.

We have studied the vapour–liquid–solid (VLS) growth of free-standing GaN wires on various III–V substrates using metalorganic vapour phase epitaxy. The low-temperature deposition including in situ droplet formation was investigated applying 1.1-dimethylhydrazine and trimethylgallium. In particular, the surface structure of BP and GaN intermediate layers on the growth of GaN wires is discussed. Furthermore, the GaN growth was examined with a special focus on the influence of triethylboron on the droplet formation and wire growth. Additionally, the Au-initiated VLS growth on c-plane Al2O3 is reported, where NH3 and triethylgallium have been used at usual growth conditions. Depending on the growth conditions used, the wires have hexagonal (h-GaN) wurtzite or cubic (c-GaN) zinc blende structure. The resulting nanowire diameters range from 50 to 300nm and they are up to 2μm in length.

The application of near-field imaging to optoelectronic devices and laser diodes provides subwavelength information on a device structure. The fiber tip used for near-field imaging can be used also as a local tunable optical source exciting a photocurrent in the near-field region of an investigated structure. We demonstrate the structure and layer properties of laser diodes based on triple GaAs quantum well structures in AlGaAs active region emitting at wavelength 850 nm. The near-field optical beam induced current analysis is here demonstrated. From the vertical scan across the laser facet the active region with quantum wells and p-, n-doped confinement layers are identified.

We study the temperature (10 K ... 293 K) dependence of the optical Hall effect (OHE) in modulation-doped AlxGa1-xAs:Si/GaAs (x = 0.45) superlattice structures with different quantum well thickness (dc(GaAs) = 16.9 nm and d(GaAs) = 3.7 nm) using generalized magnetooptic ellipsometry at far-infrared wavelengths. Free electrons Ire identified within the wells; but not within the doped barriers. The observed OHE can be fully explained within the Drude model and thermionic rate equations. The quantum-well free electron density (N = 1:3 x 10(17) cm(-3)) increases five times upon sample cooling within the wells with d(GaAs) = 3.7 nm, and remains constant within the wells with d(GaAs) = 16.9 nm. We describe this behavior as a steady state of three quantum well electron condensation processes: Coulomb-activation of electron states at the AlxGa1-xAs/GaAs interface, quantum-well-barrier reservoir interaction, and irreversible electron emission into the host crystal.

We used the metalorganic vapor-phase epitaxy for the growth of ZnO nanostructures on sapphire substrate. We studied the mechanism of epitaxial nanoneedle growth and the formation of quantum dots (QDs) into amorphous ZnO. The precursor combination diethylzinc (DEZn) and N2O was used for needle growth via the vapor liquid solid mechanism with evaporated gold films and for “initiator free” needle growth without catalyst. The needle orientations, the epitaxial relationships between ZnO and Al2O3 substrate and the dependences on growth parameters were investigated using scanning electron microscopy and X-ray diffraction measurements. For the growth of ZnO QDs iso-propanol (i-PrOH) was used as oxygen source. The QDs with radius of only few nanometers were embedded into amorphous ZnO. They show blue-shifted cathodoluminescence spectra and their mean diameter depends on the supersaturation in the gas phase.

We report on the catalyst-free growth of GaAs and InAs nanowires using the selective-area metal organic vapor phase epitaxy (SA-MOVPE). The nanowires were grown from small circular openings defined by electron-beam lithography and wet chemical etching of a thin SiNx layer. This layer was deposited on a (111)B-oriented GaAs substrate using plasma enhanced chemical vapor deposition. We optimized the growth conditions for realizing extremely uniform arrays in a triangular lattice of GaAs and InAs nanowires with diameters down to 100nm and a length of a few microns. During the growth the nanowires are formed by {1¯10} side facets and a growth direction perpendicular to the substrate surface. We investigated the growth behavior of GaAs nanowires with different diameters varying from 100 to 500nm at different growth parameters, changing the temperature and the V/III ratio of TMG and AsH3. With a combination of GaAs and InAs SA-MOVPE growth radial heterostructures were grown. The structures were characterized by scanning electron microscopy, photoluminescence spectroscopy and transmission electron microscopy.

In this work, we report on investigations of micro-dimensional heterostructures consisting of gallium arsenide and aluminium arsenide in order to obtain more information about the different growth procedure.We analysed GaAs/AlAs longitudinal heterostructures, which were grown by metal-organic vapour phase epitaxy (MOVPE) in two different ways. On the one hand an abrupt Ga to Al change and on the other hand with a continuous Ga to Al change. These columnar, longitudinal heterostructures had a diameter of approximately 1 mu m and a length of appropriately 6 mu m. The analyses were performed in the LIPSION laboratory using 2.25 MeV protons. Due to the size of the sample the beam spot size had to be focused below 1 mu m.From the RBS and PIXE measurements of the GaAs/AlAs longitudinal heterostructures we obtained the laterally resolved stoichiometry along the symmetry axis. Furthermore, impurity concentrations and oxidation processes after the growth were studied. (c) 2007 Elsevier B.V. All rights reserved.

The strain-free boron- and indium-containing GaAs compounds are promising candidates for III-V semiconductor solar cell absorber materials with lattice match to GaAs, for which experimental data of the electronic band structure are widely unknown. For nondegenerate, silicon-doped, n-type B0.03In0.06Ga0.91As with band-gap energy of 1.36eV, determined by near-infrared ellipsometry, a strong increase of the electron effective mass of 44% in B0.03In0.06Ga0.91As compared to In0.06Ga0.94As is obtained from far-infrared magneto-optic generalized ellipsometry studies. The authors thereby obtain the vibrational lattice mode behavior. For BAs, an experimentally obscure compound, the curvature of the Γ-point conduction band thus extrapolates to the free electron mass.

Lateral confinement for cylindrical micro-resonator light emitters improves the ratio of the number of the axial resonant modes to the number of the spontaneous emitting lateral modes. We have observed resonator behaviour of cylindrical microstructures as ZnO micro-pillars and glass-rods, whose lateral surfaces were coated with coaxial Bragg reflectors.

We fabricated III–V nano- and microtubes by using the bending of ultra-thin strained films by releasing them due to selective wet-chemical etching of a sacrificial layer from the substrate. The curvature is obtained by a new mechanical equilibrium shape for which the elastic strain energy of the layer-system is minimal. The resulting diameter of these tubes depends on the layer composition, layer thickness, substrate orientation and rolling direction. We studied the influence of thickness variations on the surface due to multiatomic steps on the structural properties of BGaAs/InGaAs-tubes grown on (110)-oriented GaAs-substrates. Cross-sectional transmission electron microscopy (TEM)-images on the rolled structures showed, that the large difference of the outer and inner diameter depends on the multiatomic steps at the surface of the layer-system. We also present a new material-system for the fabrication of rolled-up nanotubes (RUNTs): BGaP/InGaP with AlGaP sacrificial layer on (110)-oriented GaP-substrate. The tube diameter and the internal strain in the rolled and unrolled multilayer systems were modeled using continuum strain theory.

Magneto-transport properties of n- and p-type (B,Ga,In)As and (Ga,In)(N,As) were studied in the temperature range from 2 to 300 K and in magnetic fields up to 10 T and at hydrostatic pressures up to 16 kbar. The magneto-transport in (B,Ga,In)As and (Ga,In)(N,As) is very similar. P-type samples show normal semiconductor behaviour whereas the electron transport in both alloys is strongly affected by the interaction of the free carriers with the density of states of localized B and N impurity states, respectively. (C) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We studied the influence of the substrate preparation and the growth conditions important to fabricate GaAs nanowires (NWs) with metal-organic vapor phase epitaxy. The growth parameters temperature, precursor partial pressures and growth duration were investigated. The definite choice of the V/III ratio enables NW length growth independent on the diameter. By investigating the temporal evolution of the GaAs-NW growth a diameter-dependent growth rate could be determined. Applying nanosphere lithography arranged GaAs-NW arrays were achieved. The NWs morphology and real structure was investigated using (high-resolution) transmission electron microscopy and selective area diffraction. The twin formation in GaAs NWs was investigated. A crystallographic model is presented.

The infrared (100–600cm−1) optical properties of partially CuPt-type ordered Al0.52In0.48P deposited lattice matched on GaAs are studied by ellipsometry. The authors determine the ordinary and extraordinary dielectric functions and report on the evolution of the optical phonon mode frequencies of Al0.52In0.48P as a function of the degree of ordering. In addition to the InP- and AlP-like phonon modes, they observe two alloy-induced phonon modes which are anisotropic upon CuPt ordering. The observed modes are associated to vibrations with E and A1 symmetries. The alloy-induced phonon modes are useful for classifying the degree of ordering in this indirect band gap alloy.

We fabricated III–V nano‐ and microtubes with a diameter in the range of 140 nm to 6 µm using strained heterostructures with high quality interfaces, which were grown by metal‐organic vapor‐phase epitaxy (MOVPE). Investigations of the two‐layer system BGaAs/InGaAs which forms tubes by selective etching of an AlAs sacrificial layer are presented. Calculations of the tube diameter and the internal strain using continuum strain theory dependent on the layer thickness and composition were made. We also fabricated AlGaAs/InGaAs microtubes containing a GaAs quantum well (QW) in different sections of the AlGaAs barrier material and studied the optical properties of this embedded QW using photo‐ and cathodoluminescence spectroscopy at different temperatures. By measuring the luminescence peak‐shift of the QW caused by uniaxially stress, we were able to verify our calculations of the radial profile of the strain within the microtube wall. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

GaN x P 1−x alloy represents a novel compound semiconductor that has attracted considerable interest as a candidate for realization of light emitting diodes (LEDs) in the green-red range of the visible spectra. Simple GaN x P 1−x /GaP LED structures grown by low-preassure metalorganic vapor phase epitaxy and containing different N contents (0.6–2.3%) were investigated. The hierarchy of N complexes that generate different bound states were determined from photocurrent and electroluminescence spectra for different N concentrations in the GaN x P 1−x layer. From the experimental measurements, it was confirmed that the electroluminescence emission peaks show discrete emission maxima at ∼608 nm and ∼628 nm with increasing N content due to formation of N clusters.

Lateral confinement for cylindrical micro-resonator light emitters improves the ratio of the number of the axial resonant modes to the number of the spontaneous emitting lateral modes. We have observed resonator-behaviour of cylindrical micro-structures, whose lateral surfaces were coated with coaxial MgO/ZrO2 and a-Si/SiOχ Braggre flectors. Glass rods with circularly shaped basal planes and ZnO wires with hexagonally shaped basal planes were used as cavity material. Bragg-reflectors were deposited using pulsed laser deposition and plasma enhanced chemical vapour deposition at the lateral surface of the ZnO wires and the glass rods. The optical properties of the Bragg-reflectors were investigated using a confocal micro-reflectometer, spatially resolved spectroscopic ellipsometry technique, and spatially resolved cathodoluminescence measurements.