GaAs/GaAsBi coaxial multishell nanowires were grown by molecular beam epitaxy. Introducing Bi results in a characteristic nanowire surface morphology with strong roughening. Elemental mappings clearly show the formation of the GaAsBi shell with inhomogeneous Bi distributions within the layer surrounded by the outermost GaAs, having a strong structural disorder at the wire surface. The nanowire exhibits a predominantly ZB structure from the bottom to the middle part. The polytipic WZ structure creates denser twin defects in the upper part than in the bottom and middle parts of the nanowire. We observe room temperature cathodoluminescence from the GaAsBi nanowires with a broad spectral line shape between 1.1 and 1.5 eV, accompanied by multiple peaks. A distinct energy peak at 1.24 eV agrees well with the energy of the reduced GaAsBi alloy band gap by the introduction of 2% Bi. The existence of localized states energetically and spatially dispersed throughout the NW are indicated from the low temperature cathodoluminescence spectra and images, resulting in the observed luminescence spectra characterized by large line widths at low temperatures as well as by the appearance of multiple peaks at high temperatures and for high excitation powers.

The concept of band engineering dilute nitride semiconductors into nanowires is introduced. Using plasma-assisted molecular beam epitaxy, dilute nitride GaAsN/GaAs heterostructure nanowires are grown on silicon (111) substrates. Growth of the nanowires under high As overpressure results in a regular wire diameter of 350 nm with a length exceeding 3 μm. The GaAsN/GaAs nanowires show characteristics including favorable vertical alignment, hexagonal cross-sectional structure with {110} facets, regions of wurtzite and zinc-blende phases, and a core-shell-type heterostructure. The nanowires are composed of GaAsN shells containing up to 0.3% nitrogen surrounding GaAs cores. Panchromatic cathodoluminescence images show intensity modulation along the length of the nanowires that is possibly related to the interfaces of wurtzite/zinc-blende regions. Photoluminescence with peak wavelengths between 870 and 920 nm is clearly observed at room temperature. The spectral red shift depends on the amount of introduced nitrogen. These results reveal a method for precise lattice and band engineering of nanowires composed of dilute nitride semiconductors.

We investigate fundamental issues on the growth of GaAs/GaAsN core–shell heterostructure nanowires (NWs) by plasma-assisted molecular beam epitaxy. A Ga catalyst crystallizes during growth interruption at a high As pressure, and afterwards the growth dominantly progresses mainly increasing the NW diameter, thereby forming a wire shell. The shell diameter increases linearly depending on growth time and group III flux, similarly to the growth mechanism of planar layers. The lateral growth rate is 0.19 times lower than the growth rate of planar GaAs on a (100) substrate. At a substrate temperature 570 °C, nitrogen incorporation is inefficient in the shell layer. At a substrate temperature of 430 °C, the nitrogen is effectively introduced under continuous plasma irradiation during the growth of the GaAsN shell, resulting in the introduction of nitrogen within the shell estimated up to about 0.5%.

Nanowire (NW) lasers operating in the near-infrared spectral range are of significant technological importance for applications in telecommunications, sensing, and medical diagnostics. So far, lasing within this spectral range has been achieved using GaAs/AlGaAs, GaAs/GaAsP, and InGaAs/GaAs core/shell NWs. Another promising III–V material, not yet explored in its lasing capacity, is the dilute nitride GaNAs. In this work, we demonstrate, for the first time, optically pumped lasing from the GaNAs shell of a single GaAs/GaNAs core/shell NW. The characteristic “S”-shaped pump power dependence of the lasing intensity, with the concomitant line width narrowing, is observed, which yields a threshold gain, g th , of 3300 cm–1 and a spontaneous emission coupling factor, β, of 0.045. The dominant lasing peak is identified to arise from the HE21b cavity mode, as determined from its pronounced emission polarization along the NW axis combined with theoretical calculations of lasing threshold for guided modes inside the nanowire. Even without intentional passivation of the NW surface, the lasing emission can be sustained up to 150 K. This is facilitated by the improved surface quality due to nitrogen incorporation, which partly suppresses the surface-related nonradiative recombination centers via nitridation. Our work therefore represents the first step toward development of room-temperature infrared NW lasers based on dilute nitrides with extended tunability in the lasing wavelength.

Radiative carrier recombination processes in GaAs/GaNAs core/shell nanowires grown by molecular beam epitaxy on a Si substrate are systematically investigated by employing micro-photoluminescence (mu-PL) and mu-PL excitation (mu-PLE) measurements complemented by time-resolved PL spectroscopy. At low temperatures, alloy disorder is found to cause localization of photo-excited carriers leading to predominance of optical transitions from localized excitons (LE). Some of the local fluctuations in N composition are suggested to lead to strongly localized three-dimensional confining potential equivalent to that for quantum dots, based on the observation of sharp and discrete PL lines within the LE contour. The localization effects are found to have minor influence on PL spectra at room temperature due to thermal activation of the localized excitons to extended states. Under these conditions, photo-excited carrier lifetime is found to be governed by non-radiative recombination via surface states which is somewhat suppressed upon N incorporation. (C) 2014 AIP Publishing LLC

Optical transitions in GaNAs bulk layer containing 2.2% N have been studied with microphotoluminescence ͑-PL͒ and photoreflectance. At low temperatures and low excitation conditions, the-PL spectra showed sharp PL lines of 100-300 eV widths about 10-20 meV below the energy gap. Those lines were attributed to the recombination of localized excitons trapped at local potential minima. When the excitation power was increased, an additional smooth PL band appeared at the higher-energy side. This band corresponds to the light-hole transition in photoreflectance spectrum, i.e., transition between the delocalized states.

We report the growth of GaAs/GaNAs/GaAs core-multishell nanowires having N compositions exceeding 2%. The structures were grown by plasma-assisted molecular beam epitaxy using constituent Ga-induced vapor-liquid-solid growth on Si(111) substrates. The GaNAs shell nominally contains 0%, 2%, and 3% nitrogen. The axial cross-sectional scanning transmission electron microscopy measurements confirm the existence of core-multishell structure. The room temperature micro-photoluminescence measurements reveal a red-shift of the detected emission with increasing N content in the nanowires, consistent with the expected changes in the GaNAs bandgap energy due to the bowing effect.

We control the formation of Bi-induced nanostructures on the growth of GaAs/GaAsBi core–shell nanowires (NWs). Bi serves as not only a constituent but also a surfactant and nanowire growth catalyst. Thus, we paved a way to achieve unexplored III–V nanostructures employing the characteristic supersaturation of catalyst droplets, structural modifications induced by strain, and incorporation into the host GaAs matrix correlated with crystalline defects and orientations. When Ga is deficient during growth, Bi accumulates on the vertex of core GaAs NWs and serves as a nanowire growth catalyst for the branched structures to azimuthal <112>. We find a strong correlation between Bi accumulation and stacking faults. Furthermore, Bi is preferentially incorporated on the GaAs (112)B surface, leading to spatially selective Bi incorporation into a confined area that has a Bi concentration of over 7%. The obtained GaAs/GaAsBi/GaAs heterostructure with an interface defined by the crystalline twin defects in a zinc-blende structure can be potentially applied to a quantum confined structure. Our finding provides a rational design concept for the creation of GaAsBi based nanostructures and the control of Bi incorporation beyond the fundamental limit.