Metallorganic Vapor Phase Epitaxy Research Articles

The effect of post-growth interruption on the formation of InGaAs/GaAs quantum dots obtained by MOVPE

In this work, the study of formation regimes of In0.8Ga0.2As quantum dots on GaAs surface by metallorganic vapour-phase epitaxy has been carried out. The influence of post-growth interruption after the quantum dots deposition on the optical and physical properties of the formed objects has been investigated. It has been established that the interruption time of 2-5 seconds is optimal for the In0.8Ga0.2As/GaAs material system and growth conditions. For the chosen interruption time, the quality of formed quantum dots and their physical sizes were estimated using transmission electron microscopy: lateral size is 10 – 20 nm, height is not exceeding 5 nm and concentration is ∼9.8·1010 cm−2.

Kinetic Analysis of GaN-MOVPE via Thickness Profiles in the Gas Flow Direction with Systematically Varied Growth Conditions

We carried out a kinetic analysis of metallorganic vapor phase epitaxy (MOVPE) of GaN to investigate the dependence of the growth rate on the process conditions as a function of residence time of the precursors in the reactor. The wafer was not rotated during growth, allowing us to analyze the thickness profile of the film in the direction of gas flow, and hence the dependence of the growth rate on the residence time. The growth rate is determined mainly by the concentration of the growth species and mass transfer of the growth species to the wafer surface. The growth rate peaked in the flow direction, and the position of this peak could, in most cases, be explained by considering a combination of the linear gas velocity and the time constant for vertical diffusion of trimethylgallium (TMGa) and/or growth species across the NH3 feed stream to the wafer surface. In some cases this was not possible, indicating that more complex effects were significant. This work is expected to contribute to understanding of the reaction pathways for GaN-MOVPE, and the growth rate data reported here are expected to provide useful benchmarks for growth simulations that combine computational fluid dynamics and reaction models.

Parabolic tailored-potential quantum-wires grown in inverted pyramids

Quasi-one-dimensional AlGaAs quantum wires (QWRs) with parabolic heterostructure profiles along their axis were fabricated using metallorganic vapor phase epitaxy (MOVPE) on patterned (111)B GaAs substrates. Tailoring of the confined electronic states via modification in the parabolic potential profile is demonstrated using model calculations and photoluminescence spectroscopy. These novel nanostructures are useful for studying the optical properties of systems with dimensionality between zero and one.

Determination of hardness and Young's modulus for important III–V compound semiconductors

Nanoindentation was used to determine material hardness and Young's modulus in a wide compositional range of GaAsxP1−x, Ga1−xInxP, Ga1−xInxAs and Al0.5Ga1−xInxAs compound semiconductors. Ternary and quaternary samples were grown on misoriented GaAs(001) and Si(001) substrates by metallorganic vapor phase epitaxy. Nanoindentation measurements were made using a Berkovich shaped indenter in a continuous stiffness mode. This method allows a continuous measurement of modulus and hardness over the complete indentation depth. Parabolic and linear trends were found for the Young's modulus of the investigated compound semiconductors. In case of hardness, parabolic trends associated with solid solution strengthening were found for all investigated material systems.

Photoelectrochemical Conditioning of MOVPE p-InP Films for Light-Induced Hydrogen Evolution: Chemical, Electronic and Optical Properties

Homoepitaxial p-InP(100) thin films prepared by MOVPE (metallorganic vapor phase epitaxy) were transformed into an InP/oxide-phosphate/Rh heterostructure by photoelectrochemical conditioning. Surface sensitive synchrotron radiation photoelectron spectroscopy indicates the formation of a mixed oxide constituted by In(PO3)3, InPO4 and In2O3 as nominal components during photo-electrochemical activation. The operation of these films as hydrogen evolving photocathode proved a light-to-chemical energy conversion efficiency of 14.5%. Surface activation arises from a shift of the semiconductor electron affinity by 0.44 eV by formation of In-Cl interfacial dipoles with a density of about 1012 cm−2. Predominant local In2O3-like structures in the oxide introduce resonance states near the semiconductor conduction band edge imparting electron conductivity to the phosphate matrix. Surface reflectance investigations indicate an enhanced light-coupling in the layered architecture.

Extraction of plasticity parameters of GaN with high temperature, in situ micro-compression

Micro-pillar compression has been utilised in a novel elevated temperature technique, in situ in the SEM to characterise the plasticity of gallium nitride (GaN) {0001}-oriented euhedral prisms grown by metallorganic vapor phase epitaxy. Electron backscatter diffraction was used to confirm the orientation of the prisms, and deformation was observed to occur via 2nd order pyramidal slip on the {112¯2}〈112¯3〉 slip system. Analysis of the micro-compression data allowed extraction of fundamental deformation parameters of GaN from 24.5 to 479.3°C. The strain rate sensitivity parameter was determined to be 0.0234±0.0073 both by constant strain rate micro-compressions and micro-compression strain rate jump tests. The measured activation volume was 3.88±0.13×10−29m3, and the activation energy was 0.9±0.2eV.

Fabrication and growth of GaN-based micro and nanostructures

GaN is considered as the material of choice for electromechanical, electronic and optoelectronic applications in the visible/UV regions of the electromagnetic spectrum. However, the lack of an adapted substrate results in a very large density of defects, in particular dislocations, stacking faults and cracks. Under these circumstances, the growth of nanostructures appears as an appealing means of circumventing the problem. In this paper, we describe the fabrication and characterisation of GaN–based nanostructures – cantilevers, microdiscs, photonic crystals, micro and nanowires – grown by metallorganic vapour phase epitaxy (MOVPE) and molecular beam epitaxy (MBE) and fabricated either by a bottom–up or a top–down approach. The applications envisaged at CRHEA will be examined.

Dilute nitride InGaAsN/GaAs V-groove quantum wires emitting at 1.3 μm wavelength at room temperature

Site-controlled InGaAsN quantum wires (QWRs) emitting at 1.3 μm at room temperature were grown on V-grooved GaAs substrates by modulated-flux metallorganic vapor phase epitaxy. The nonplanar substrate template is shown to enhance the nitrogen uptake, evidenced by a redshift in photoluminescence wavelength twice larger for the QWRs than for the adjacent quantum well regions. The mechanism of this increase in nitrogen incorporation efficiency, achieved without degradation in optical properties, is explained by the extended gradient of In content at the step-rich QWR interfaces.

High-quality 1.3 μm-wavelength GaInAsN/GaAs quantum wells grown by metalorganic vapor phase epitaxy on vicinal substrates

We investigated the composition and optical properties of GaInAsN/GaAs single quantum wells (QWs) grown on vicinal-(001) GaAs substrates using metallorganic vapor phase epitaxy with modulated nitrogen-precursor flux. A significant enhancement in N incorporation and photoluminescence efficiency is achieved with such optimized QW structures. Possible mechanisms of the observed increase in N uptake and reduction in defect density, related to the substrate vicinality, are discussed.

Photoluminescence of Eu-doped GaN

ABSTRACTThis talk reviews work on the optical properties of Eu-doped GaN at the Semiconductor Spectroscopy laboratory of the University of Strathclyde. The principal experimental technique used has been lamp-based Photoluminescence/Excitation (PL/E) spectroscopy on samples produced mainly by high-energy ion implantation and annealing, either at low or high pressures of nitrogen, as described by Lorenz et al. [1]. These have been supplemented by samples doped in-situ either by Molecular Beam Epitaxy or Metallorganic Vapour Phase Epitaxy. Magneto-optic experiments on GaN:Eu were carried out in collaboration with the University of Bath.

GaN stripes on vertical {111} fin facets of (110)-oriented Si substrates

Selective sidewall epitaxy of AlN/GaN is reported on vertical fins of silicon using metallorganic vapor phase epitaxy. Silicon (110) wafers are structured to form fins with {111} sidewall facets. AlN buffer layers are grown with uniform thickness on vertical {111} surfaces, followed by GaN which grows selectively on the AlN to form the sidewall fin structures. Raman measurements of the GaN show very narrow line widths, consistent with excellent material quality. Spatial dependence from microcathodoluminescence mapping of the GaN band gap emission shows compressive strain in the GaN relaxes closer to the fin corners.

Study of Luminescence from GaN : Tb3 + Powders and Thin Films Deposited by MOVPE and PLD Methods

Due to the recent commercial interest in nitride-based optoelectronics and rare-earth emission in nitride materials, the structural and optical characteristics of powders and thin films have been investigated in this work. The powder samples were made using a three-step solution method. Pulsed laser deposition (PLD) and metallorganic vapor phase epitaxy (MOVPE) methods were utilized for depositing films on sapphire substrates. The GaN powders with activator concentrations up to 8 atom % exhibited luminescence due to the transitions under cathodoluminescence (CL) as well as under photon excitation. Both near-band-edge emission and activator emission have been observed in PLD thin films made from the corresponding powders. X-ray diffraction revealed polycrystalline PLD thin films with a preferred growth direction along the axis, while scanning electron micrographs showed rough film morphology with submicrometer particles. CL emission from accompanied by near-band-edge emission and defect emissions from the GaN host was observed for the MOVPE films made using tris(2,2,6,6-tetramethyl-3,5-heptanedionato)terbium but not films made with tris(isopropylcyclopentadienyl)terbium. Despite visible luminescence from in GaN powders and thin films, no energy transfer from the host to activator ions was observed. This suggests that is unlikely to fluoresce if used in a GaN-based optoelectronic device.

Parasitic Interlayer at the GaAs-on-InGaP Interface in MOVPE InGaP ∕ GaAs : A Study by the Chemically Sensitive (200) Diffraction

The chemically sensitive (200) diffraction in the dark field (DF) mode of transmission electron microscopy has been used to detect, identify, and evaluate the composition of the parasitic interlayer at the GaAs-on-InGaP interface in metallorganic vapor-phase epitaxy (MOVPE) heterostructures. The latter were grown at with no growth interruption. The composition range determined by (200) DF was further refined by using the X-ray diffraction result that the interlayer has a negative lattice mismatch to GaAs. The parasitic interlayer can be either or with and . intermixing and In segregation are assumed to drive the formation of the interlayer. The low In content in the quaternary is ascribed to the reduced In segregation at . In segregation is likely favored by the tensile strain associated with the interlayer in its process of growth.

High-power single-mode laser diodes based on carbon-doped quantum-well InGaAs/AlGaAs heterostructures

Emission parameters of single-mode laser diodes based on InGaAs/GaAs/AlGaAs heterostructures doped with carbon and grown by using the metallorganic vapour phase epitaxy (MOVPE) technique are studied. The obtained results show that maintaining a certain doping profile ensuring optimisation of series resistance and internal optical losses during all fabrication stages of the active element of a diode laser, provides for enhancement of the laser efficiency. Based on laser heterostructures studied in this paper, highly efficient single-transverse-mode laser diodes emitting 300 mW at 980 nm have been manufactured.

Study of GaN : Eu3 + Thin Films Deposited by Metallorganic Vapor-Phase Epitaxy

Using metallorganic vapor-phase epitaxy, thin films of gallium nitride activated by have been deposited on sapphire substrates at atmospheric pressure. Luminescence from ions in GaN has been investigated using photoluminescence (PL) and PL excitation spectroscopy. Experimental results show that ions are excited via energy transfer from the host. Analyses of the observed emission and excitation spectra indicate occupancy of multiple sites in the nitride lattice. Using a pulsed laser source, variation of emission intensity with increasing excitation intensity has also been examined. The possibility of emission saturation at high excitation intensity is discussed from the perspective of application in light-emitting diode sources.

1150-nm wavelength InGaAs/GaAs VCSELs incorporating regrown tunnel junctions

Results of the development of all metallorganic vapor-phase epitaxy (MOVPE) GaAs-based vertical cavity surface emitting lasers (VCSELs) with a regrown tunnel junction (TJ) emitting at ∼1150-nm wavelength are presented. A zero-bias-specific resistance of ∼3×10 −4 Ω cm 2 has been obtained for the GaAs-based TJ structure. VCSEL devices incorporating 4–7-μm and 12-μm TJ mesas exhibit an ∼2–3 mA threshold current. Room-temperature lasing spectra are multimode with an output power of 1 and 2 mW, respectively, and thermal roll-over is above 25 mA. A 2×2 VCSEL array of 3-μm aperture elements at 7-μm pitch yielding 0.8 mW room-temperature output power has been realized.

High Photocatalytic Activity of Heterojunction of Zinc Selenide Grown on Nanoscaled Titanium Oxide

High-quality nanoscaled anatase phase titanium oxide can be obtained from the conversion of ammonium oxotrifluorotitanate by the thermal treatment in oxygen. The photocatalytic activity of nanoscaled titanium oxide obtained at the thermal treatment temperature of shows the highest photocatalytic activity and is times of commercial P-25. The energy bandgap of ZnSe is near the maximum intensity of solar spectrum and acts as a sensitizer. The heterojunction of zinc selenide/titanium oxide prepared by metallorganic vapor-phase epitaxy shows 2.0 times the photocatalytic activities of commercial P-25.

Magnetic characterization of ZnO doped with vanadium

The magnetic properties of vanadium doped ZnO nanorods formed by different growth methods were examined. The samples under investigation were either grown by metallorganic vapour-phase epitaxy (MOVPE) with in situ incorporation of the V atoms or by aqueous chemical growth (ACG) in combination with an ion-implantation process. The V concentration for all samples was less than 2 at.%. Field-cooled SQUID measurements only reveal a weak ferromagnetic signal still in a very sensitive measuring range. However, the MFM micrographs obtained at room temperature show a clear magnetic contrast and complex structures, the images are in good agreement with the phase images expected for vertically aligned magnetic dipoles. This is a strong indication for a ferromagnetic behaviour at room temperature.

Application of electron holography to the determination of contact potential difference in an AlGaN/AlN/Si heterostructure

Electron holography was applied to determine the contact potential differences in an AlGaN/AlN/Si heterostructure formed by metallorganic vapor phase epitaxy. Since mean inner potentials are generally different for different materials, their values before and after forming the junction were evaluated first, then the contact potential difference was obtained by subtracting the difference of the mean inner potentials before forming the junction from the corresponding difference after forming the junction. The contact potential differences thus obtained were consistent with a reported asymmetric nonlinear behavior in the current-voltage characteristics measured for a similar heterojunction diode.

High Photocatalytic Activity of Nanoscaled Heterojunction of ZnS Grown on Fluorine and Nitrogen Co–doped TiO2

High-quality nanoscaled fluorine and nitrogen co–doped anatase-phase titanium oxide can be obtained from the conversion of ammonium oxotrifluorotitanate by thermal treatment. The photocatalytic activity of titanium oxide treated at shows the highest photocatalytic activity and is about 1.31 times of P-25 due to higher fluorine and nitrogen doping. The heterojunction of zinc sulfide/titanium oxide prepared by metallorganic vapor-phase epitaxy shows 1.51 times the photocatalytic activities of commercial P-25. Both nanoscaled titanium oxide and zinc sulfide/titanium oxide heterojunction show a proportional relationship between carrier lifetime and photocatalytic activity.