Growth and characterisation of Zn:LiNbO3/Mg:LiNbO3 multilayer thin films grown by liquid phase epitaxy

1, 3 and 5 mol% ZnO doped LiNbO₃ film and 2 mol% MgO doped LiNbO₃ multilayer films were grown on the LiNbO₃ (001) substrate by liquid phase epitaxy (LPE) method with a Li₂O‐V₂O₅ system. We examined the optical transmission spectra of the Zn:LiNbO₃ by Fourier Transform‐Infrared Spectrophotometer (FT‐IR). The crystallinity and the lattice mismatch between the Zn:LiNbO₃ film and Mg:LiNbO₃ film was confirmed by x‐ray rocking curve (XRC) and observed the ZnO and MgO distribution in the cross‐section of the multilayer thin films by electron probe micro analyzer (EPMA). Furthermore, the surface morphology of the films was observed using atomic force microscopy (AFM). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of ZnTe layers on (111) GaAs substrates by metalorganic vapor phase epitaxy

ZnTe layers were grown on (111) GaAs substrates by metalorganic vapor phase epitaxy using dimethylzinc and diethyltelluride as the source materials. X-ray diffraction analysis revealed that epitaxial ZnTe layers can be obtained on (111) GaAs substrates. X-ray rocking curves, Raman spectroscopy, and photoluminescence measurements showed that the crystal quality of ZnTe layers depends on the substrate temperature during the growth. A high-crystalline quality (111) ZnTe heteroepitaxial layer with strong near-band-edge emission at 550 nm was obtained at a substrate temperature of 440 °C.     

Luminescence of (GaAl)As layers grown by temperature gradient liquid phase epitaxy

In this paper the growth of Al_xGa_1–xAs layers with nearly constant composition along their thickness is described. By means of electroluminescence and cathodoluminescence measurements recombination mechanisms connected with the presence of Si are discussed. The aging behaviour of the light emitting diodes is supposed to depend on the AlAs content of the layers and to be connected with the diffusion of acceptors in the p-n junction region.     

Formation and characterization of GaAs/As superlattice grown by molecular beam epitaxy at low substrate temperature

High-resolution X-ray diffractometer and transmission electron microscope (TEM) are used to characterize the redistribution of As precipitates in Si δ-doped GaAs grown by molecular beam epitaxy at low substrate temperature (230°C). The superlattice satellite peaks are observed for samples annealed at 700-800°C for 10 min, which is attributed to the formation of a GaAs/As superlattice during the annealing period. The degree of As precipitates confined on the δ-doped planes is revealed on the intensity of satellite peaks in the X-ray rocking curves, as confirmed by the TEM observations. The lattice expansion and contraction of the annealed low-temperature epitaxial layers can be easily observed from the asymmetry of the satellite peaks.     

Growth mechanisms of GaAs nanowires by gas source molecular beam epitaxy

GaAs nanowires were grown on GaAs (1 1 1)B substrates in a gas source molecular beam epitaxy system, using self-assembled Au particles with diameters between 20 and 800 nm as catalytic agents. The growth kinetics of the wires was investigated for substrate temperatures between 500 and 600 °C, and V/III flux ratios of 1.5 and 2.3. The broad distribution of Au particles enabled the first observation of two distinct growth regimes related to the size of the catalyst. The origins of this transition are discussed in terms of the various mass transport mechanisms that drive the wire growth. Diffusion of the growth species on the 2-D surface and up the wire sidewalls dominates for catalyst diameters smaller than ∼130 nm on average, while direct impingement on the catalyst followed by bulk diffusion through the Au particle appears to sustain the wire growth for larger catalyst diameters. A change in wire sidewall facets, indicating a probable transition in the crystal structure, is found to be primarily dependent on the V/III flux ratio.     

Coexistence properties of phase separation and CuPt-ordering in InGaAsP grown on GaAs substrates by organometallic vapor phase epitaxy

CuPt-ordering and phase separation were directly investigated in In_1-xGa_xAs_yP_1-y with a low arsenic content grown by organometallic vapor phase epitaxy on GaAs substrates. CuPt-ordering and phase separation in samples grown at the substrate temperatures of 630 and 690 °C were characterized by transmission electron diffraction and transmission electron microscopy. Although the immiscibility of InGaAsP was enhanced at the lower substrate temperature, the sample grown at 630 °C showed less phase separation than the 690 °C-grown sample. The degree of CuPt-ordering was significantly enhanced in the sample grown at 630 °C. The results demonstrated that the CuPt-ordering originating from surface reconstruction of P(2×4) suppressed the phase separation even in the miscibility gap. The detailed characterization of the phase separation clearly revealed a vertical composition modulation (VCM) in InGaAsP for the first time. The mechanism of the VCM formation is discussed based on the modulated-strain field on the surface.     

Controlled formation of GaAs pn junctions during hydride vapor phase epitaxy of GaAs

Interface formation in HVPE GaAs was investigated through the growth of multilayer test structures with alternately doped and undoped layers and subsequently, pn diode devices. Two growth procedures were used in device formation: continuous growth of all layers, and a growth interruption with simultaneous equilibration of new gas flows for subsequent layers. These junctions were probed using SIMS to determine the doping profiles and impurity incorporation near the interfaces and throughout the bulk of the layers. The junction I–V characteristics were measured with and without illumination to correlate the junction properties with the measured photovoltaic performance. It was discovered that the use of a growth interruption leads to doping transitions up to 6x narrower than samples grown without interruption. The growth interruption leads to an interfacial Si spike that is not observed in the uninterrupted samples during growth of GaAs doped with silane. This spike does not appear to degrade either the material quality or pn junction quality, and pn diodes grown with interruption have exhibited enhanced device efficiencies under solar simulation compared with devices grown without interruption, reaching efficiencies of up to 9.2% without the use of antireflective coatings.     

A steady-state procedure of liquid phase epitaxy

A turning-shifting technique is reported permitting the deposition of epitaxial layers at constant temperatures and with small melting volumes. Basic parameters of GaAs are studied and the development of crystal growth is followed up in dependence on temperature.     

Fabrication of GaAs quantum wires by metalorganic molecular beam epitaxy and their optical properties

We have grown GaAs quantum wires having nominal cross-sectional dimensions of 20×20 nm² buried in AlGaAs layers, by lateral metalorganic molecular beam epitaxy on the terraced sidewalls of mesa-grooved ( ) substrates. In the photoluminescence spectrum of this sample at 77 K, a dominant emission has been observed at a peak wavelength of 780 nm which corresponds to a blue shift of 80 meV from the GaAs bulk transition. Emission spectroscopy from different positions and imaging by cathodoluminescence have demonstrated that this emission was generated from the sidewalls, indicating that it originates from the quantum wire.     

Surface preparation of AB semiconductors (Cd3As2, Zn3As2, Cd3P2, Zn3P2) under ultra-high vacuum conditions

The UHV surface preparation of AB materials (crystals and thin films) has been monitored with XPS and AES. Clean and stoichiometric surfaces of AB crystals were prepared by means of low energy ion bombardment and subsequent low temperature annealing. Stoichiometric Cd₃As₂ and Zn₃P₂ thin films with very low amounts of C and O were deposited by the evaporation of bulk material in the UHV. The quality of prepared AB crystal and thin film surfaces was sufficient to carry out density of states investigations (UPS, RELS) with success.     

Dependence of impurity incorporation upon substrate misorientation during GaAs growth by metalorganic vapour phase epitaxy

Doping studies of the incorporation behaviour of three different dopants (Zn, In and Si) versus the misorientation of the (100) surface during MOVPE growth of GaAs have been carried out with diethylzinc, trimethylindium and disilane as precursors. The incorporation of the dopants has been studied as function of the input mole fraction dopant, growth temperature, degree and direction of misorientation. In order to explain the results we discuss the BCF theory and the nature of the steps as function of above mentioned parameters. It appears that the BCF theory alone cannot explain the results, a counteracting mechanism has been introduced based on preferential arsenic desorption from the step edges.     

Thermally activated stress relief in garnet layers grown by liquid phase epitaxy

The lattice misfit of (Lu, Tb)₃Fe₅O₁₂ epitaxial layers grown in compression on Gd₃Ga₅O₁₂ substrates has been found to decrease as a result of annealing at temperatures between 1000 and 1300°C. The deformation rate is thermally activated and depends on the degree of compressive misfit stress at the annealing temperature, the layer thickness and the reducing nature of the anneal atmosphere. Layers which were in tension at the annealing temperature (obtained by using Y₃Fe₅O₁₂ as the substrate material) did not exhibit stress relief. The process has been found to occur nonhomogeneously by the formation of regions of almost total relief which grow and multiply with continued annealing. The shape symmetry of these regions is consistent with dislocation climb in {112} planes. The results are interpreted in terms of a mechanism involving dislocation climb loops (∽1μm diameter) which develop as a result of the formation of oxygen vacancies.     

Model for defect-free epitaxial lateral overgrowth of Si over SiO2 by liquid phase epitaxy

A growth model for defect-free epitaxial lateral overgrowth by liquid phase epitaxy is presented. Growth in the pure step flow mode and a preferential development of (111) planes in liquid phase epitaxy permit one to quantitatively predict the overgrowth. The shape and size of the Si lamellae which grow over SiO₂ depend on the crystallographic orientations of the substrate growth face and of the seeding windows. Overgrowth experiments with Si on oxidized, (111)- and (100)-oriented Si wafers serve to verify the model. Growth experiments from In and Bi solutions in temperature intervals between 950 and 800°C yield overgrowth widths up to 120 μm and aspect ratios of 40:1 on (111) oriented wafers.     

Properties of gallium- and aluminum-doped bulk ZnO obtained from single-crystals grown by liquid phase epitaxy

Bulk properties of gallium (Ga)- and aluminum (Al)-doped zinc oxide (ZnO) were studied using bulky single-crystalline thick films grown by liquid phase epitaxy (LPE). The highest possible dopant concentration was 1×10¹⁹ cm^–3 for LPE growth at around 800 °C. The electron concentration was nearly same to the Ga and Al concentrations. The donor binding energy decreased to nearly zero with an increase in dopant concentration, and electron mobility of the sample with relatively high dopant concentration (1×10¹⁹ cm^–3) was more than 60 cm² V^–1 s^–1 at room temperature. The LPE technique is a potential solution for the production of ZnO for optical applications because the well-defined excitonic luminescence could be seen from the LPE-grown-doped single-crystals.     

Growth and electrical properties of liquid phase epitaxial layers of GaxIn1-xP lattice-matched to GaAs substrates

From the measurement of the evaporation rate of phosphorus the favourable conditions for the layer growth were determined. Further, we have studied the influence of zinc and silicon on the growth and the morphology. The mobilities, the electron and hole concentrations in the temperature range from 77 to 300 K are presented. In the Si-doped samples we could not find a correlation between the silicon concentration in the melt and the donor concentrations in the layer. An estimation of the acceptor ionization energy in Zn-doped samples yields E_A = (15 ± 4) meV.     

Fabrication of InGaAs ridge quantum wires by selective molecular beam epitaxy and their characterization

InGaAs/InAlAs ridge quantum wires were successfully fabricated by selective molecular beam epitaxy (MBE) for the first time. Prior to wire fabrication, detailed data on selective growth characteristics were taken by using test structures. Then, triangular shaped InGaAs ridge quantum wires with a width of 300 å were fabricated, using the selectivity data. Photoluminescence (PL) measurements detected a strong and narrow peak from the wires which showed a blue shift of 159 meV with respect to the InGaAs band-gap. This value agrees excellently with the calculation.     

X-ray diffraction measurement of liquid As2Se3 by using third-generation synchrotron radiation

X-ray diffraction (XD) measurements of liquid As₂Se₃ were carried out in the temperature range up to 1600 °C where the temperature is well beyond the semiconductor to metal (SC–M) transition temperature around 1000 °C. The measurements were done by using third-generation synchrotron radiation at SPring-8 and the obtained structure factors have been much improved compared to previous in house XD measurements with regard to the momentum transfer range and the data statistics. The deduced pair distribution functions show that with increasing temperature, the position of the first peak does not change within the errorbar and the coordination number gradually decreases up to 1600 °C irrespective of the SC–M transition. These results coincide with those of the first-principle molecular dynamics simulation.