The characteristic surface morphologies of GaN grown by plasma-assisted molecular beam epitaxy under various growth conditions have been investigated. Three regimes (one N stable and two Ga stable) are identified on a structure diagram (Ga/N ratio versus substrate temperature). boundary between the N-stable regime (low Ga/N ratios) Ga-stable (high is determined rate films constant over range temperatures (the Ga-droplet intermediate regime) formation droplets has an Arrhenius dependence with...

We investigate the electronic states in strained Ga0.62In0.38N0.015As0.985/GaAs multiple- quantum-well structures using photoluminescence and (polarized) excitation measurements at low temperature. From a theoretical fit to experimental data, type-I band alignment for heavy holes with conduction-band offset ratio of about 80% is obtained, while light show an approximately flat alignment. Additionally, our results suggest increased effective electron mass GaInNAs, possibly due interaction...

The formation mechanisms of epitaxial GaN nanowires grown within a self-induced approach by molecular-beam epitaxy have been investigated at the onset nucleation process combining in situ reflection high-energy electron-diffraction measurements and ex high-resolution transmission electron microscopy imaging. It is shown that growth on AlN buffer layer initially governed dislocation-free coherent islands. These islands develop through series shape transitions from spherical caps truncated to...

We report a Raman study of the so-called buffer layer with periodicity which forms intrinsic interface structure between epitaxial graphene and SiC(0001). show that this leads to non-vanishing signal in spectrum at frequencies range D- G-band discuss its shape intensity. Ab initio phonon calculations reveal these features can be attributed vibrational density states layer.

GaAs nanowires (NWs) grown by molecular-beam epitaxy may contain segments of both the zincblende (ZB) and wurtzite (WZ) phases. Depending on growth conditions, we find that optical emission such NWs occurs either predominantly above or below band gap energy ZB [E(g,ZB)]. This result is consistent with assumption [E(g,WZ)] larger than E(g,ZB) alternating WZ along wire axis establish a type II alignment, where electrons captured within recombine holes neighboring segments. Thus, corresponding...

The formation mechanisms of GaN nanowires grown on a Si${}_{x}$N${}_{y}$ amorphous interlayer within self-induced approach by molecular beam epitaxy have been investigated combining in situ reflection high-energy electron-diffraction measurements with ex high-resolution transmission electron microscopy imaging. It is found that initially nucleates as spherical cap-shaped islands wetting angle $42\ifmmode\pm\else\textpm\fi{}{7}^{\ifmmode^\circ\else\textdegree\fi{}}$. Subsequently, these...

Hexagonal boron nitride (h-BN) is a layered two-dimensional material with properties that make it promising as dielectric in various applications. We report the growth of h-BN films on Ni foils from elemental B and N using molecular beam epitaxy. The presence crystalline over entire substrate confirmed by Raman spectroscopy. Atomic force microscopy used to examine morphology continuity synthesized films. A scanning electron study obtained shorter depositions offers insight into nucleation...

The authors report on electrically pumped MBE-grown VCSELs GaAs substrate with an InGaAsN active region, emitting above 1.28 µm record characteristics. CW output power at room temperature exceeds 500 µW initial slope efficiency of 0.17 W/A.

The authors report on the generation of 8 W optical power at 1.3 µm under continuous wave (CW) operation from a 100 aperture an InGaAsN single quantum well laser. laser was facet-coated and active region maintained 10°C by heatsinking. A preliminary lifetime test produced no noticeable degradation characteristics after 1000 hours CW output 1.5 W. Threshold current densities as low 335 A/cm2 were measured such broad area lasers. These values are significant improvement over previously...

We present a comprehensive theoretical and experimental analysis of 1.3-μm InGaAsN/GaAs lasers. After introducing the 10-band k /spl middot/ p Hamiltonian which predicts transition energies observed experimentally, we employ it to investigate laser properties ideal real devices. Our calculations show that addition N reduces peak gain differential at fixed carrier density, although saturation value as function radiative current density are largely unchanged due incorporation N. The...

By measuring the spontaneous emission (SE) from normally operating /spl sim/1.3-/spl mu/m GaInNAs-GaAs-based lasers we have quantitatively determined variation of each current paths present in devices as a function temperature 130 K to 370 K. From SE measurements determine how I close threshold, varies carrier density n, which enables us separate out main corresponding monomolecular (defect-related), radiative or Auger recombination. We find that defect-related recombination forms sim/55%...

On Si(1 1 1) and Si(0 0 1), GaN nanowires (NWs) form in a self-induced way without the need for any external material. sapphire, NW growth is induced by Ni collectors. Both types of NWs exhibit wurtzite crystal structure grow Ga-polar C-direction perpendicular to substrate. The sidewalls are M-plane facets, although on Ni-induced also A-plane segments form, if temperature low. collector-induced free strain epitaxially aligned substrate, but particular former show significant spread tilt...

We determine with high precision the growth rate of self-induced GaN nanowires grown by molecular beam epitaxy under various conditions from scanning electron micrographs taking into account in situ measurements initial incubation time, which is needed before nanowire starts. In order to quantitatively describe dependence on gallium flux, and temperature, we develop a detailed theoretical model diffusion-induced specifically for approach, i.e., without any droplet at top. The fits are...

The oscillating piezoelectric fields accompanying surface acoustic waves are able to transport charge carriers in semiconductor heterostructures. Here, we demonstrate high-frequency (above 1 GHz) GaAs-based nanowires deposited on a substrate. short wavelength of the modulation, smaller than length nanowire, allows trapping photo-generated electrons and holes at spatially separated energy minima maxima conduction valence bands, respectively, their along nanowire with well defined velocity...

Vertical GaN nanowires are grown in a self-induced way on sputtered Ti film by plasma-assisted molecular beam epitaxy. Both situ electron diffraction and ex ellipsometry show that is converted to TiN upon exposure of the surface N plasma. In addition, ellipsometric data demonstrate this be metallic. The evidence have strict epitaxial relationship film. Photoluminescence spectroscopy shows excitonic transitions virtually identical spectral position, line width, decay time those...

We propose a platform for observing the Josephson diode effect: Andreev molecule. This nonlocal electronic state is hosted in circuits made of two closely spaced junctions, through hybridization states. The effect occurs at level one individual junction while other generates required time-reversal and spatial-inversion symmetry breaking. present microscopic description this phenomenon based on fermionic states, focusing single channels short limit, we compute both supercurrent energy...

An evaluation algorithm for the determination of chemical composition strained hexagonal epitaxial films is presented. This able to separate influence strain and on lattice parameters measured by x-ray diffraction. The measurement symmetric asymmetric reflections delivers a c films. These are used calculate relaxed employing theory elasticity. From parameters, film can be determined Vegard's rule. has been applied InGaN/GaN/Al2O3(00.1) heterostructures.

Recombination processes in Ga1−xInxNyAs1−y/GaAs multiple quantum wells (MQWs) were investigated as function of the nitrogen molar fraction. We found a pronounced S-shaped behavior for temperature-dependent shift photoluminescence emission similar to ternary nitrides InGaN and AlGaN. This is explained by exciton localization at potential fluctuations. Time-resolved measurements 4 K reveal an increase decay time with decreasing energy. A model based on lateral transfer lower-energy states...

A growth diagram for molecular beam epitaxy of AlN on sapphire and 6H–SiC was established using reflection high energy electron diffraction, atomic force microscopy, Rutherford backscattering spectrometry. In varying the Al/N ratio temperature, distinctive surface morphologies emerge, which are assigned to three regimes growth, one N-rich (Al/N<1) two Al-rich (Al/N>1) regimes. Under conditions, films exhibit rough morphologies. contrast, conditions produce excellent smooth...

Room temperature, continuous-wave operation at 1.3 µm is reported for InGaAsN triple quantum well lasers. The layers were grown by MBE using an RF-coupled plasma source nitrogen. Large broad area lasers exhibit very low threshold current density down to 680 A/cm2 and a slope efficiency of 0.59 W/A (output per two facets). Maximum output powers 2.4 4 W are reached 10°C under CW pulsed operation, respectively. These values significant improvement over those previously published in the material system.

Pseudomorphic InGaAs/GaAs multiple quantum well structures with In contents ranging from 18 to 25% were grown by molecular beam epitaxy and investigated optical absorption, photoluminescence, electronic Raman scattering. Sharp exciton peaks linewidths of ∼3 meV for the first electron heavy hole transition are observed in absorption spectra. The subband structure was independently energies analyzed using a four-band effective mass Schrödinger equation taking strain into account. A...

The effects of GaN nanowire coalescence have been investigated on a local scale by combining high-resolution transmission electron microscopy imaging with spatially resolved cathodoluminescence measurements. Coalescence induces the formation network boundary dislocations, above which I1-type basal-plane stacking faults are nucleated. former contributes to reduction in crystalline quality at bottom coalesced nanowires while latter leads intense excitonic radiative transitions 3.42 eV their...

GaN nanowires (NWs) were grown on sapphire by molecular beam epitaxy. NWs form only in the presence of Ni seed particles and under N-rich conditions. Their length increases linearly with growth time up to about 7.5μm while their diameter remains almost constant. In contrast, a switch Ga-rich conditions after NW formation results radial growth, i.e., lengthening is negligible. These corroborate fact that III-V governed accumulation group-III atoms seeds, group-V species are not preferentially...

We studied the doping with Si and Be of GaAs nanowires (NWRs) grown by molecular beam epitaxy. Regarding NW morphology, no influence was observed for but high concentrations cause a kinking tapering NWRs. investigated local vibrational modes means resonant Raman scattering to determine incorporation sites dopant atoms. For doping, both donors on Ga acceptors As have been observed. found be incorporated as an acceptor sites. However, at concentration, is also interstitial