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Radial GaInP/AlGaInP nanowire array light-emitting diodes (LEDs) are promising candidates for novel high-efficiency solid state lighting due to their potentially large strain-free active emission volumes compared to planar LEDs. Moreover, by proper tuning of the diameter of the nanowires, the fraction of emitted light extracted can be significantly enhanced compared to that of planar LEDs. Reports so far on radial growth of nanowire LED structures, however, still point to significant challenges related to obtaining defect-free radial heterostructures. In this work, we present evidence of optically active growth-induced defects in a fairly broad energy range in vertically processed radial GaInP/AlGaInP quantum well nanowire array LEDs using a variety of complementary experimental techniques. In particular, we demonstrate strong infrared electroluminescence in a spectral range centred around 1 eV (1.2 μm) in addition to the expected red light emission from the quantum well. Spatially resolved cathodoluminescence studies reveal a patchy red light emission with clear spectral features along the NWs, most likely induced by variations in QW thickness, composition and barriers. Dark areas are attributed to infrared emission generated by competing defect-assisted radiative transitions, or to trapping mechanisms involving non-radiative recombination processes. Possible origins of the defects are discussed. [ABSTRACT FROM AUTHOR]

Nanowire array ensembles contacted in a vertical geometry are extensively studied and considered strong candidates for next generations of industrial scale optoelectronics. Key challenges in this development deal with optimization of the doping profile of the nanowires and the interface between nanowires and transparent top contact. Here we report on photodetection characteristics associated with doping profile variations in InP nanowire array photodetectors. Bias-dependent tuning of the spectral shape of the responsivity is observed which is attributed to a Schottky-like contact at the nanowire–ITO interface. Angular dependent responsivity measurements, compared with simulated absorption spectra, support this conclusion. Furthermore, electrical simulations unravel the role of possible self-gating effects in the nanowires induced by the ITO/SiOx wrap-gate geometry. Finally, we discuss possible reasons for the observed low saturation current at large forward biases. [ABSTRACT FROM AUTHOR]

The phonon energies of AlGaP in wurtzite crystal structure are generally not known, as opposed to their zincblende counterparts, because AlGaP crystallizes in zincblende phase in bulk and thin films structures. However, in nanowires AlGaP can be grown in wurtzite crystal structure. In this work we have grown wurtzite GaP/AlGaP/GaP core–shell nanowires by use of MOVPE. After developing suitable growth conditions, the Al composition was determined by STEM-EDX measurements and the wurtzite AlGaP phonon energies by Raman spectroscopy. Raman measurements show a peak shift with increasing Al composition in the AlGaP shell. We find that the phonon energies for wurtzite AlGaP are slightly lower than for zincblende AlGaP. Our results can be used to determine the Al composition in wurtzite AlGaP by Raman scattering. [ABSTRACT FROM AUTHOR]

Ternary nanowires (NWs) often exhibit varying material composition along the NW growth axis because of different diffusion properties of the precursor molecules. This constitutes a problem for optoelectronic devices for which a homogeneous material composition is most often of importance. Especially, ternary GaInP NWs grown under a constant Ga–In precursor ratio typically show inhomogeneous material composition along the length of the NW due to the complexity of low temperature precursor pyrolysis and relative rates of growth species from gas phase diffusion and surface diffusion that contribute to synthesis of particle-assisted growth. Here, we present the results of a method to overcome this challenge by in situ tuning of the trimethylindium molar fraction during growth of ternary Zn-doped GaInP NWs. The NW material compositions were determined by use of x-ray diffraction, scanning transmission electron microscopy and energy dispersive x-ray spectroscopy and the optical properties by photoluminescence spectroscopy. [ABSTRACT FROM AUTHOR]

We report on the influence of hydrogen bromide (HBr) in situ etching on the growth of InP, GaP and GaAs nanowires. We find that HBr can be used to impede undesired radial growth during axial growth for all three material systems. The use of HBr opens a window for optimizing the growth parameters with respect to the materials’ quality rather than only their morphology. Transmission electron microscopy (TEM) characterization reveals a partial transition from a wurtzite crystal structure to a zincblende upon the use of HBr during growth. For InP, defect-related luminescence due to parasitic radial growth is removed by use of HBr. For GaP, the etching with HBr reduced the defect-related luminescence, but no change in peak emission energy was observed. For GaAs, the HBr etching resulted in a shift to lower photon emission energies due to a shift in the crystal structure, which reduced the wurtzite segments. [ABSTRACT FROM AUTHOR]