Wurtzite single crystal GaN nanocolumns were grown by plasma-assisted molecular beam epitaxy on bare Si(001) substrates. Nanocolumns with diameters in the range of 20–40nm have no traces extended defects and they grow aligned along [0001] direction. Photoluminescence measurements evidence a very high quality terms intense narrow excitonic emissions. Raman scattering data show that are strain-free. These results open way to an efficient integration optoelectronic devices complementary metal...

Abstract The growth conditions to achieve group‐III‐nitride nanocolumns and nanocolumnar heterostructures by plasma‐assisted molecular beam epitaxy are studied. evolution of the morphology with is determined for (Ga,Al)N (In,Ga)N nanocolumns. mechanisms behind under high N‐rich clarified in sense that no seeding or catalysts required, as it case vapour‐liquid‐solid model applies most grown metal organic chemical vapour deposition, either group‐III nitrides, II–VI III–V compounds. Some...

A majority of the point defects in GaN that are responsible for broad photoluminescence (PL) bands remain unidentified. One them is green luminescence band (GL2) having a maximum at 2.35 eV which was observed previously undoped grown by molecular-beam epitaxy Ga-rich conditions. The same PL Mg-doped GaN, also very unique properties GL2 allowed us to reliably identify it different samples. best candidate defect causes nitrogen vacancy $({V}_{\mathrm{N}})$. We propose transitions electrons...

The polar nature of the wurtzite crystalline structure GaN and ZnO results in existence a spontaneous electric polarization within these materials their associated alloys (Ga,Al,In)N (Zn,Mg,Cd)O. polarity has also important consequences on stability different crystallographic surfaces, this becomes especially when considering epitaxial growth. Furthermore, internal fields may adversely affect properties optoelectronic devices but is used as potential advantage for advanced electronic...

We experimentally investigate whether crystal polarity affects the growth of GaN nanowires in plasma-assisted molecular beam epitaxy and their formation has to be induced by defects. For this purpose, we prepare smooth coherently strained AlN layers on 6H-SiC(0001) SiC(000$\bar{1}$) substrates ensure a well-defined an absence structural morphological On N-polar AlN, homogeneous dense nanowire array forms, evidencing that form spontaneously Al-polar do not observe Ga-polar NWs. Instead,...

We investigate the axial and radial growth of GaN nanowires upon a variation Ga flux during molecular beam epitaxial growth. An increase in promotes without affecting rate. In contrast, decrease reduces rate any change radius. These results are explained by kinetic model that accounts for both diffusion adatoms along side facets towards nanowire tip finite amount active N available The explains formation new equilibrium radius after increasing provides an explanation two well known but so...

The morphology of GaN samples grown by plasma-assisted molecular beam epitaxy on Si(111) was systematically studied as a function impinging Ga/N flux ratio and growth temperature (750-850{\deg}C).Two different regimes were identified: compact nanocolumnar. A diagram established parameters, exhibiting the transition between regimes, showing under which conditions cannot be due to thermal decomposition Ga desorption. Present results indicate that adatoms diffusion length actual growing surface...

Thermal decomposition of wurtzite (0001)-oriented GaN was analyzed: in vacuum, under active N exposure, and during growth by rf plasma-assisted molecular beam epitaxy. The rate determined measurements the Ga desorption using situ quadrupole mass spectrometry, which showed Arrhenius behavior with an apparent activation energy 3.1 eV. Clear signatures intensity oscillations reflection high-energy electron diffraction facilitated complementary evaluation highlighted a layer-by-layer mode...

The realization of semiconductor structures with stable excitons at room temperature is crucial for the development excitonics and polaritonics. Quantum confinement has commonly been employed enhancing excitonic effects in heterostructures. Dielectric confinement, which potentially much stronger, proven to be more difficult achieve because rapid nonradiative surface/interface recombination hybrid dielectric-semiconductor structures. Here, we demonstrate intense emission from bare GaN...

We demonstrate an all-epitaxial and scalable growth approach to fabricate single-crystalline GaN nanowires on graphene by plasma-assisted molecular beam epitaxy. As substrate, we explore several types of epitaxial layer structures synthesized SiC. The different differ mainly in their total number layers. Because is found be etched under active N exposure, the direct only achieved multilayer structures. analysis nanowire ensembles prepared Raman spectroscopy transmission electron microscopy...

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 demonstrate the self-assembled growth of vertically aligned GaN nanowire ensembles on a flexible Ti foil by plasma-assisted molecular beam epitaxy. The analysis single nanowires transmission electron microscopy reveals that they are crystalline. Low-temperature photoluminescence spectroscopy demonstrates that, in comparison to standard grown Si, prepared exhibit equivalent crystalline perfection, higher density basal-plane stacking faults, but reduced inversion domain boundaries....

Real-time analysis of the growth modes during homoepitaxial (0001)GaN by plasma-assisted molecular beam epitaxy was performed using reflection high energy electron diffraction. A mode map established as a function Ga/N flux ratio and temperature, exhibiting distinct transitions between three-dimensional (3D), layer-by-layer step-flow mode. The to transition under Ga-rich surfactant mediated related Ga adlayer coverage one monolayer. Under N-rich conditions from 3D predominantly thermally...

We use line-of-sight quadrupole mass spectrometry to monitor the spontaneous formation of GaN nanowires on Si during molecular beam epitaxy. find that temporal evolution nanowire ensembles is well described by a double logistic function. The analysis prepared under wide variety growth conditions allows us construct diagram which can be used predict average delay time precedes formation.

We investigate the nucleation, growth, and coalescence of spontaneously formed GaN nanowires in molecular beam epitaxy combining statistical analysis scanning electron micrographs with Monte Carlo growth models. find that (i) nanowire density is limited by shadowing substrate from impinging fluxes already existing nanowires, (ii) shortly after nucleation stage, radial becomes negligible, (iii) caused bundling nanowires. The latter phenomenon driven gain surface energy at expense elastic...

Self-assembled columnar AlGaN/GaN nanocavities, with an active region of GaN quantum disks embedded in AlGaN nanocolumn and cladded by top bottom AlN/GaN Bragg mirrors, were grown. The nanocavity has no cracks or extended defects, due to the relaxation at Si interface free-surface volume ratio. emission from matched peak reflectivity tuning Al content thickness. Quantum confinement effects that depend on both disk thickness inhomogeneous strain distribution within are clearly observed.

An alternative approach is presented for the plasma-assisted molecular beam epitaxy of high-quality GaN. Under N-rich growth conditions, an unexpected layer-by-layer mode was found a wide range temperatures in GaN thermal decomposition regime (>750°C). Consequently, superior surface morphologies with roughness less than 1nm (rms) have been achieved. For lightly Si-doped films, room-temperature electron mobilities exceeding 1100cm2∕Vs were measured, surpassing commonly insulating...

We investigate the nature of excitons bound to I1 basal-plane stacking faults [(I1;X)] in GaN nanowire ensembles by continuous-wave and time-resolved photoluminescence spectroscopy. Based on linear increase radiative lifetime these with temperature, they are demonstrated exhibit a two-dimensional density states, i. e., fault acts as quantum well. From slope increase, we determine oscillator strength (I1;X) show that value obtained reflects presence large internal electrostatic fields across...

We investigate the structural and optical properties of spontaneously formed GaN nanowires with different degrees coalescence. This quantity is determined by an analysis cross-sectional area perimeter obtained plan-view scanning electron microscopy. X-ray diffraction experiments are used to measure inhomogeneous strain in nanowire ensembles as well orientational distribution nanowires. The comparison results for prepared on bare Si AlN buffered 6H-SiC reveals that main source random...

Single GaN nanowires formed spontaneously on a given substrate represent nanoscopic single crystals free of any extended defects. However, due to the high area density thus nanowire ensembles, individual coalesce with others in their immediate vicinity. This coalescence process may introduce strain and structural defects, foiling idea defect-free material geometry. To investigate consequences this process, quantitative measure ensembles is required. We derive objective criteria determine...

In molecular beam epitaxy, the spontaneous formation of GaN nanowires on Si(111) substrates at elevated temperatures is limited by long incubation time that precedes nanowire nucleation. this work, we present three unconventional growth approaches to minimize and thus facilitate significantly higher (up 875$^{\circ}$C). We achieve by: (i) using III/V flux ratios larger than one compensate for Ga desorption, (ii) introducing a two-step procedure, (iii) an AlN buffer layer favor The ensembles...

Carrier confinement effects in nanocolumnar ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ multiple quantum disks have been studied by photoluminescence, as a function of the Al content and disk thickness. Experimental emission energies are compared to theoretical calculations based on one-dimensional Schr\"odinger-Poisson solver, including spontaneous piezoelectric polarizations, surface potentials, strain. An inhomogeneous biaxial (in-plane) strain...

Indium incorporation and surface morphology of InAlN layers grown on (0001) GaN by plasma-assisted molecular beam epitaxy were investigated as a function the impinging In flux substrate temperature in 450–610 °C range. was found to decrease with due thermal decomposition growing layer, while for given it increased until stoichiometry reached at growth front. The InN losses during followed an Arrhenius behavior characterized activation energy 2.0 eV. A diagram highly instrumental identify...