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We investigated the optical properties of wurtzite (WZ) GaP nanowires by performing photoluminescence (PL) and time-resolved PL measurements in the temperature range from 4K to 300 K, together with atom probe tomography to identify residual impurities in the nanowires. At low temperature, the WZ GaP luminescence shows donor-acceptor pair emission at 2.115 eV and 2.088 eV, and Burstein-Moss band-filling continuum between 2.180 and 2.253 eV, resulting in a direct band gap above 2.170 eV. Sharp exciton α-β-γ lines are observed at 2.140-2.164-2.252 eV, respectively, showing clear differences in lifetime, presence of phonon replicas, and temperaturedependence. The excitonic nature of those peaks is critically discussed, leading to a direct band gap of ~2.190 eV and to a resonant state associated with the c-line ~80 meV above the Γ8C conduction band edge. [ABSTRACT FROM AUTHOR]

We present an initial study of the influence of the growth parameters on the surface morphology and on the interface quality of homoepitaxial GaP(1 1 1) and heteroepitaxial GaP/AlGaP(1 1 1) grown on GaP(1 1 1)B substrates using Gas-Source Molecular Beam Epitaxy (GSMBE). Three different surface reconstructions are identified in the RHEED patterns during the growth runs. The Root Mean Square (RMS) surface roughness measured post-growth by AFM ranges from 3 to 10 nm over 10 × 10 µm 2 areas, for a film thickness of 100–600 nm. The results of 2θ-ω XRD scans on (1 1 1) and (3 1 1) planes reveal a stacking disorder in the AlGaP layer and further XRD phi-scan measurements on GaP (3 1 1) show strong peaks with 3-fold rotational symmetry and additional of 3-fold weak peaks indicating only a negligible fraction of the twinned crystal orientation in the substrate. TEM images of these samples show a smooth interface between the AlGaP layer and GaP substrate, and reveal the presence of a high density of extended defects such as stacking faults, twinning and dislocations lines in AlGaP layer whereas the GaP layer appears as pure Zinc-Blende. Further TEM analysis reveals composition and local strain variations for GaP/AlGaP samples associated with an undulated surface. [ABSTRACT FROM AUTHOR]

The structural and optical properties of GaP and GaPN layers synthesized by molecular-beam epitaxy on Si(100) substrates misoriented by 4° are studied. The possibility of producing GaP buffer layers that exhibit a high degree of heterointerface planarity and an outcropping dislocation density of no higher than ~2 × 10 cm is shown. Emission from the Si/GaP/GaPN structure in the spectral range of 630-640 nm at room temperature is observed. Annealing during growth of the Si/GaP/GaPN structure makes it possible to enhance the room-temperature photoluminescence intensity by a factor of 2.6, with no shift of the maximum of the emission line. [ABSTRACT FROM AUTHOR]

Wurtzite gallium phosphide (WZ GaP) has been predicted to exhibit a direct bandgap in the green spectral range. Optical transitions, however, are only weakly allowed by the symmetry of the bands. While efficient luminescence has been experimentally shown, the nature of the transitions is not yet clear. Here we apply tensile strain up to 6% and investigate the evolution of the photoluminescence (PL) spectrum of WZ GaP nanowires (NWs). The pressure and polarization dependence of the emission together with a theoretical analysis of strain effects is employed to establish the nature and symmetry of the transitions. We identify the emission lines to be related to localized states with significant admixture of G7c symmetry and not exclusively related to the G8c conduction band minimum (CBM). The results emphasize the importance of strongly bound state-related emission in the pseudodirect semiconductor WZ GaP and contribute significantly to the understanding of the optoelectronic properties of this novel material. [ABSTRACT FROM AUTHOR]

In this report, we have measured the current – voltage characteristics and the relative light intensity of two different GaP based light emitting diodes (LEDs), namely, L-53HD and L-53GD in a temperature range from 350 K to 110 K and the variation of relative light intensity as a function forward current are measured only at 350 K and 110 K. From the opto-electrical characterizations we obtained the values of the ideality factor, forward voltage and the relative light intensity emitted by the LED at different temperatures. The variations of these data show that temperature has a significant influence on different properties of such LEDs. These results are analysed by their associate theories. Finally, it is important to note that an optimization among the different parameter values, while some increasing and others decreasing with temperature change, as indicated in the present study, is essential and must be considered for design involving the device, particularly, for any low temperature application. [ABSTRACT FROM AUTHOR]

III–V semiconductor nanowires(NWs) have gained significantinterest as building blocksin novel nanoscale devices. The one-dimensional (1D) nanostructurearchitecture allows one to extend band structure engineering beyondquantum confinement effects by utilizing formation of different crystalphases that are thermodynamically unfavorable in bulk materials. Itis therefore of crucial importance to understand the influence ofvariations in the NWs crystal structure on their fundamental physicalproperties. In this work we investigate effects of structural polytypismon the optical properties of gallium phosphide and GaP/GaNP core/shellNW structures by a correlative investigation on the structural andoptical properties of individual NWs. The former is monitored by transmissionelectron microscopy, whereas the latter is studied via cathodoluminescence(CL) mapping. It is found that structural defects, such as rotationaltwins in zinc blende (ZB) GaNP, have detrimental effects on lightemission intensity at low temperatures by promoting nonradiative recombinationprocesses. On the other hand, formation of the wurtzite (WZ) phasedoes not notably affect the CL intensity neither in GaP nor in theGaNP alloy. This suggests that zone folding in WZ GaP does not enhanceits radiative efficiency, consistent with theoretical predictions.We also show that the change in the lattice structure have negligibleeffects on the bandgap energies of the GaNP alloys, at least withinthe range of the investigated nitrogen compositions of <2%. BothWZ and ZB GaNP are found to have a significantly higher efficiencyof radiative recombination as compared with that in parental GaP,promising for potential applications of GaNP NWs as efficient nanoscalelight emitters within the desirable amber-red spectral range. [ABSTRACT FROM AUTHOR]

We demonstrate excitation of surface phonon polaritons on patterned gallium phosphide surfaces. Control over the light-polariton coupling frequencies is demonstrated by changing the pattern periodicity and used to experimentally determine the gallium phosphide surface phonon polariton dispersion curve. Selective emission via out-coupling of thermally excited surface phonon polaritons is experimentally demonstrated. Samples are characterized experimentally by Fourier transform infrared reflection and emission spectroscopy, and modeled using finite element techniques and rigorous coupled wave analysis. The use of phonon resonances for control of emissivity and excitation of bound surface waves offers a potential tool for the exploration of long-wavelength Reststrahlen band frequencies. [ABSTRACT FROM AUTHOR]

We present a study of self-assembled In0.5Ga0.5As quantum dots on GaP(001) surfaces linking growth parameters with structural, optical, and electronic properties. Quantum dot densities from 5.0 × 107 cm-2 to 1.5 × 1011 cm-2 are achieved. A ripening process during a growth interruption after In0.5Ga0.5As deposition is used to vary the quantum dot size. The main focus of this work lies on the nature of optical transitions which can be switched from low-efficient indirect to high-efficient direct ones through improved strain relief of the quantum dots by different cap layers. [ABSTRACT FROM AUTHOR]

Abstract: We report on the quantitative study of microtwins (MT) defects in the GaP/Si(001) thin film grown by Molecular Beam Epitaxy and the optical properties of GaAsP(N)/GaP(N) quantum wells grown on top of the GaP/Si pseudo-substrates. A 780nm photoluminescence at room temperature from the GaAsPN quantum wells is measured on silicon. Time-resolved photoluminescence has been performed and evidences the influence of non-radiative defects originated from the GaP/Si interface. The structural defects such as MT are quantitatively analyzed by synchrotron X-ray diffraction (XRD) combined with transmission electron microscopy (TEM) analyses. We show that the XRD measurements are in good agreement with TEM observation and reveal a strong contribution of MT in the [111] direction. The MT density appears to be directly correlated with the growth temperature. [Copyright &y& Elsevier]

Abstract: AlGaP alloy and InGaAs/GaP quantum dots are studied toward possible solutions for the cladding layers and the active zone of a pseudomorphic laser structure on silicon. Coherent growth of AlGaP layers on GaP substrate is carefully analysed by X-ray reciprocal space mapping. The influence of Al content on refractive index is studied by spectroscopic ellipsometry. The structural and optical properties of InGaAs/GaP quantum dots are respectively studied by scanning tunnelling microscopy and time-resolved photoluminescence experiments. [Copyright &y& Elsevier]

Recombination processes in GaP/GaNP core/shell nanowires (NWs) grown on Si are studied by employing temperature-dependent continuous wave and time-resolved photoluminescence (PL) spectroscopies. The NWs exhibit bright PL emissions due to radiative carrier recombination in the GaNP shell. Though the radiative efficiency of the NWs is found to decrease with increasing temperature, the PL emission remains intense even at room temperature. Two thermal quenching processes of the PL emission are found to be responsible for the degradation of the PL intensity at elevated temperatures: (a) thermal activation of the localized excitons from the N-related localized states and (b) activation of a competing non-radiative recombination (NRR) process. The activation energy of the latter process is determined as being around 180 meV. NRR is also found to cause a significant decrease of carrier lifetime. [ABSTRACT FROM AUTHOR]

It is shown in this paper that tin dioxide coating is suitable to enhance sensitivity of photodiodes operating in the ultraviolet spectral range and based on zinc selenide and gallium phosphide. For these materials, the sensitivity values have been increased up to 0.12 and 0.2 A/W, respectively, in the maxima of their spectral characteristics. It is also shown that the film silicon nitride -- silicon dioxide a bit better clarifies silicon photodiode, especially at the wavelength 700 nm. A gluing composition, in general, worsens transmission of films, and to greater extent transmission of the above film. [ABSTRACT FROM AUTHOR]