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Organic–inorganic hybrid (OIH) materials have emerged as a high-performance class of light emitters, which can be used as phosphors for optically pumped white-light-emitting diodes (WLEDs). Here, w...

Hybrid organic–inorganic halides containing Bi and Sb generally exhibit higher stability and lower toxicity compared to Pb analogues. In this work, the synthesis, crystal and electronic structures and optical properties of a brand-new methylammonium bismuth iodide, (MA)4Bi6I22 (MA+ = CH3NH3+), are reported. Interestingly, we find that the presence of the HgI2 is necessary for the targeted preparation of (MA)4Bi6I22. (MA)4Bi6I22 contains isolated [Bi6I22]4− clusters made of six edge-sharing octahedral BiI6 units, which are separated by MA+ cations in its 0D crystal structure. A relatively low optical band gap of 1.9 eV was estimated for (MA)4Bi6I22 based on diffuse reflectance measurements. An intense photoluminescence peak emerges at 636 nm at low temperatures that supports the assigned band gap value. Electronic structure calculations show the presence of flat bands in the valence and conduction bands, consistent with the low-dimensional structure of (MA)4Bi6I22, and slightly indirect nature of the bandgap. Our findings suggest that the use of facilitator moieties such as HgI2 may provide a pathway to obtaining alternative methylammonium bismuth iodides to (MA)3Bi2I9.

Atomic layers of Black Phosphorus (BP) present unique opto-electronic properties dominated by a direct tunable bandgap in a wide spectral range from visible to mid-infrared. In this work, we investigate the infrared photoluminescence of BP single crystals at very low temperature. Near-bandedge recombinations are observed at 2 K, including dominant excitonic transitions at 0.276 eV and a weaker one at 0.278 eV. The free-exciton binding energy is calculated with an anisotropic Wannier-Mott model and found equal to 9.1 meV. On the contrary, the PL intensity quenching of the 0.276 eV peak at high temperature is found with a much smaller activation energy, attributed to the localization of free excitons on a shallow impurity. This analysis leads us to attribute respectively the 0.276 eV and 0.278 eV PL lines to bound excitons and free excitons in BP. As a result, the value of bulk BP bandgap is refined to 0.287 eV at 2K., 12 pages, 3 figures - Main text 13 pages, 6 figures - Supporting information

International audience; Antimony-doped ZnO layers have been grown by metalorganic vapour-phase epitaxy on sapphire and ZnO substrates at high-temperature (950 °C) and low-pressure conditions (50 torr). Nitrous oxide and diethyl-zinc have been used as oxygen and zinc precursors, respectively. The incorporation of antimony has been obtained from the decomposition of triethylantimony doping molecules added in the gas phase. High Sb concentrations were measured from 1019 to 1021 at/cm−3 using secondary ion mass spectroscopy and depend on the nature and the orientation on the substrate. Low-temperature photoluminescence spectra of Sb-doped layers exhibit donor–acceptor pair transitions at 3.253 eV. Unlike Raman spectra of nitrogen-doped ZnO layers which show several local vibrational modes related to nitrogen incorporation, these modes were found to be absent in the antimony-doped ZnO layers. Transmission electron microscopy suggests that the incorporation of Sb is partly related to dislocations and other structural defects. All together, the characterizations suggest the formation of acceptor dopant–defect complexes, such as SbZn-2VZn. Finally, ZnO:Sb/n-ZnO homojunction diodes have been successfully elaborated on ZnO substrate. The current–voltage characteristics of the device exhibit a rectifying behaviour with a turn-on voltage of 3 V.

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International audience; We report syntheses, crystal and electronic structures, and characterization of three new hybrid organic−inorganic halides (R)ZnBr 3 (DMSO), (R) 2 CdBr 4 · DMSO, and (R)CdI 3 (DMSO) (where (R) = C 6 (CH 3) 5 CH 2 N(CH 3) 3 , and DMSO = dimethyl sulfoxide). The compounds can be conveniently prepared as single crystals and bulk polycrystalline powders using a DMSO−methanol solvent system. On the basis of the single-crystal X-ray diffraction results carried out at room temperature and 100 K, all compounds have zero-dimensional (0D) crystal structures featuring alternating layers of bulky organic cations and molecular inorganic anions based on a tetrahedral coordination around group 12 metal cations. The presence of discrete molecular building blocks in the 0D structures results in localized charges and tunable room-temperature light emission, including white light for (R)ZnBr 3 (DMSO), bluish-white light for (R) 2 CdBr 4 ·DMSO, and green for (R)CdI 3 (DMSO). The highest photoluminescence quantum yield (PLQY) value of 3.07% was measured for (R)ZnBr 3 (DMSO), which emits cold white light based on the calculated correlated color temperature (CCT) of 11,044 K. All compounds exhibit fast photoluminescence lifetimes on the timescale of tens of nanoseconds, consistent with the fast luminescence decay observed in π-conjugated organic molecules. Temperature dependence photoluminescence study showed the appearance of additional peaks around 550 nm, resulting from the organic salt emission. Density functional theory calculations show that the incorporation of both the low-gap aromatic molecule R and the relatively electropositive Zn and Cd metals can lead to exciton localization at the aromatic molecular cations, which act as luminescence centers.

The metal–organic chemical vapor deposition growth of various Ga-doped ZnO nanostructures for plasmonics is investigated, with a particular focus on the nanowire facet transformations induced by the addition of trimethylgallium in the gas phase. For nonintentionally doped spontaneous ZnO nanowires, the aspect ratio is strongly decreased due to residual Ga in the reactor, and the shape evolves rapidly toward Christmas-tree-like and hierarchical structures upon intentional Ga doping. Regarding ZnO/ZnO:Ga core–shell structures, a change of the smooth initial M-oriented facets occurs, with the development of {2021} surfaces, and further {1011} and {0001} surfaces. Interestingly, a similar evolution of the lateral roughness is observed in Au-catalyzed doped nanowires. High concentrations of Ga in the grown nanostructures are revealed by photoluminescence and confirmed by Rutherford backscattering spectrometry. First photoacoustic measurements show an optical absorption at 6 μm, evidencing that the degenerate...

International audience; Organic–inorganic hybrid perovskites (OIHP) are developing rapidly as high-performance semiconductors for solid-state solar cells and light emitting devices. Recently, lead-halide two-dimensional (2D) OIHP were found to present bright broadband visible emission, thus, highlighting their potential as single component white-light (WL) emitters. This contribution deals with the preparation of a new Cd-based 2D hybrid perovskite, of the chemical formula (C6H11NH3)2CdBr4 (abbreviated as compound 1), of which structural and optical properties have been studied and analyzed. Room temperature optical absorption (OA) measurements, performed on spin-coated film of compound 1, revealed a sharp excitonic absorption peak at 3.24 eV, and a large exciton binding energy of 377 meV, estimated from low temperature OA spectrum. Upon 325 nm irradiation, compound 1 showed a very broadband WL emission consisting of one peak at 2.94 eV, attributed to exciton confined in the [CdBr4]2– inorganic layers, and a second peak at 2.53 eV resulting from the cyclohexylammonium cations emission. Temperature dependence of PL spectra evidenced anomalous behavior accompanied by singularities around 50 and 150 K in the integrated intensity, the full width at half-maximum and the PL peaks positions. These singularities have been traced back to structural phase transitions, from temperature dependence powder and single crystal X-ray diffraction investigations, from which strong correlations had emerged between the structural distortion of the CdBr6 pseudo-octahedron and the broadening characteristics of the WL emission band. These hitherto unrecognized properties turn this and similar OIHP into perspective candidates for potential applications as WL-emitting diodes.

We have investigated the optical properties of ZnO nanowires grown by metalorganic chemical vapor deposition (MOCVD) with nitrous oxide (N2O) as oxygen precursor. Photoluminescence (PL) and Raman measurements showed the influence of adsorbed molecules on the optical properties. Low-temperature (4 K) PL studies on the surface exciton (SX) at 3.3660 eV elucidated the nature and origin of this emission. In particular, surface treatment by annealing at high temperature under inert gas reduced the emission intensity of SX. Raman vibrational spectra proved that presence of a considerable amount of adsorbed molecules on the surface of ZnO nanowires plays a key role in the occurrence of surface excitons.

International audience; We report an in-depth analysis of ZnO micropods emission. A strong correlation between defect and interband emissions is observed. ZnO micropods were grown using low-temperature chemical bath deposition (CBD). ZnO micropods exhibited perfectly-crystalline hexagonally-shaped facets with various numbers of branches. Raman studies showed that ZnO micropods contained trapped zinc hydroxide (OH) and imidogen (NH) defects that originate from the precursor solution used in the CBD technique. These defects were evacuated by thermal annealing, leading to the recrystallization in the volume of the micropods and the formation of structural defects at their surface, as attested by scanning electron microscopy and X-ray diffraction. More importantly, the thermal annealing was accompanied by a breakdown of the NH defects, which resulted in a nitrogen doping of the ZnO micropods. The structural changes as well as the nitrogen doping resulted in a drastic change in the photoluminescence (PL) spectrum of the ZnO micropods that exhibited a stronger free exciton UV emission as well as a stronger visible (white) emission. An in-depth low-temperature PL study of both UV and visible emission reveals a strong interplay between the structural-defect bound excitonic UV emission (Y-band) and the deep donor (visible) emission, which suggests a rather complex emission mechanism involving an efficient nonradiative energy transfer between the Y-band states and defect states leading to the enhanced visible emission of ZnO micropods after high temperature annealing.

International audience; Deuterium diffusion is investigated in nitrogen-doped homoepitaxial ZnO layers. The samples were grown under slightly Zn-rich growth conditions by plasma-assisted molecular beam epitaxy on m-plane ZnO substrates and have a nitrogen content [N] varied up to 5 × 1018 at cm-3 as measured by secondary ion mass spectrometry (SIMS). All were exposed to a radio frequency deuterium plasma during 1 h at room temperature. Deuterium diffusion is observed in all epilayers, while its penetration depth decreases as the nitrogen concentration increases. This is strong evidence of a diffusion mechanism limited by the trapping of deuterium on a nitrogen-related trap. The SIMS profiles are analyzed using a two-trap model including a shallow trap, associated with a fast diffusion, and a deep trap, related to nitrogen. The capture radius of the nitrogen-related trap is determined to be 20 times smaller than the value expected for nitrogen-deuterium pairs formed by coulombic attraction between D+ and nitrogen-related acceptors. The (N2)O deep donor is proposed as the deep trapping site for deuterium and accounts well for the small capture radius and the observed photoluminescence quenching and recovery after deuteration of the ZnO:N epilayers. It is also found that this defect is by far the N-related defect with the highest concentration in the studied samples.

In this present work, ZnO and ZnMgO thin films prepared by a sol-gel process were deposited on glass substrates via spin coating technique. The structural, morphological and optical properties of the obtained films were investigated. X-ray diffraction study revealed that all layers exhibit a hexagonal wurtzite structure without any secondary phase segregation. The atomic force microscopy (AFM) depicts that the grains size of ours samples decreases as magnesium content increases. The absorption spectra obtained on ZnMgO thin films show a band gap tuning from 3.19 to 3.36 eV, which is also consistent with blue shifting of near-band edge PL emission, measured at low temperature. The incorporated amount of magnesium was calculated and confirmed by EDX. The gas sensing performances were tested in air containing NO 2 for different operating temperatures. The experimental result exhibited that ZnMgO sensors shows a faster response and recovery time than the ZnO thin films. The resistivity and the sensor response as function of Mg content were also investigated.

A simple and cost-effective sol–gel technique was employed to elaborate ZnO and Zn(1−x)CdxO thin films deposit by spin coating onto the c- and r-plane sapphire substrates. The deposited films were characterized for their structural, morphological and optical properties using high resolution X ray diffraction (HRXRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) as function of Cd incorporation and employed substrate. Higher Cd incorporation (4.5%) is obtained for ZnCdO layer deposited on r-plane sapphire, which is confirmed by the greatest energy shift (110 meV) to lower energy measured by low temperature photoluminescence. X-ray diffraction study revealed that all films are polycrystalline with a hexagonal wurtzite structure. A preferred orientation along [001] and [110] direction is obtained respectively for layer deposited on c- and r-plane sapphire. However, the (002) and (110) XRD layers peak were shifted towards the lower 2θ values after Cd incorporation showing a slight variation of cell parameters. SEM and AFM image show no very significant variation in the morphology of the layers depending on the substrate orientation and Cd content incorporated. A mixture of large and small hexagonal grains are obtained which are more pronounced for ZnCdO deposited on r-plane sapphire and their agglomeration leaves more empty space in films. The gas sensing performances were tested in NO2 containing air for different operating temperatures as function of Cd incorporation and sapphire substrate orientation. The experimental result exhibited that ZnCdO sensors deposited on r-plane sapphire shows a more better gas response with fast response and recovery time at moderate operating temperatures as Cd contend increase.

ZnO nanowires have been grown by metalorganic chemical vapor deposition on sapphire substrates. The use of N2O and DEZn as oxygen and zinc precursors combined with high temperature leads to the spontaneous growth of vertical ZnO nanowires (NWs) on underlying three dimensional islands present at the bottom of each nanowire. These nanowires are grown along the c axis of the wurtzite structure, exhibit well defined m-plane facets and are free of extended defects. This configuration is favorable to band-gap engineering studies. Based on this, we have grown a series of radial ZnO/ZnMgO shells and quantum wells with different thicknesses and Mg concentrations. ZnxMg1-xO alloys have been grown using O2, (MCp)2Mg and DEZn as oxygen, magnesium and zinc precursors. Low temperature photoluminescence spectroscopy and transmission electron microscopy have assessed Mg concentrations in the shell up to 20 %. Electron diffraction reveals that the ZnMgO alloyed structure is, at least partially, ordered. Micro-photoluminescence performed on a single ZnO/ZnMgO coreshell nanowire including a quantum well exhibits luminescence properties, with a lateral quantum confined emission. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Atomic layers of Black Phosphorus (BP) have been recently isolated, ten years after graphene. BP stands out in the 2D-materials panorama by its unique semiconducting properties: direct bandgap which can be tuned by the layer number in a wide range of wavelengths from visible (monolayer) to midinfrared (bulk) [1]. This tunability combined the anisotropy of the structure therefore offers promising perspectives in various fields such as electronics and photonics. However, the fast photooxidation in ambient condition, coupled to a high sensitivity to quantum confinement and dielectric environment in ultrathin BP, make very difficult the investigations on its intrinsic optical properties [2]. Further, as screening effects may strongly affect electronic and spectroscopic properties of 2D materials, it is highly desirable to investigate intrinsic properties of free-standing layers as well the ones of the bulk material which remain poorly known. To start with, we have investigated photoluminescence (PL) and absorption properties of high quality BP single crystals at 2K [FTIR]. The PL intensity appears comparable to high quality InAs crystals confirming the suitability of BP for infrared applications. Two peaks are evidenced at 0.275 eV and 0.26 eV. The highest energy peak is particularly narrow (FWHM = 3.8meV) and is tentatively attributed to exciton recombination, thanks to the temperature dependence of PL spectra from 2K to 300K. Further, we have measured the gap related energy shift of the PL spectra as a function of the BP thickness in a series of mechanically exfoliated samples with thicknesses down to 10 nm, complementary to the previous measures done on thinner samples [3]. As far as the thinnest layers are concerned, which cannot manipulated in air, we have shown that Angular resolved Electron energy loss spectroscopy implemented in Transmission Electron Microscopy (Ar-EELS-TEM) offers a unique way to investigate dielectric response of free-standing layers related to valence band and plasmon excitations with the advantage to get access to their q dispersion and their symmetry properties [4]. By combining this technique with suitable ab initio calculations, we have studied the dielectric response of free-standing BP layers as a function of the number of layers. We found optical bandgap values of 1.9 eV, 1.4 eV and 1.1 eV for the mono- bi- and trilayer respectively. Moreover, by combining our results with a simple variational model, we correlate the exciton energy with the dielectric screening. We hence demonstrate that the variations of the electronic gap are sizeably larger than the variations of the binding energy. Finally, we probe and analyze the volume and surface plasmons dispersion as a function of momentum for the 1-3 BP layers and bulk and highlight a deviation and linearization of the parabolic dispersion with strong anisotropic fingerprints [5]. [1] G. Zhang et al., Nat. Com., 8, 14071, (2017) [2] A. Favron, E. Gaufres et al Nature Mat. 14 (2015) 826. [3] C. Chen et al., NanoLett., (2019) [4] F. Fossard et al, Phys. Rev. B 96, 115304 (2017) [5] E. Gaufres et al, Nanoletters (2019); DOI: 10.1021/acs.nanolett.9b03928

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The annealing effects of c-plane sapphire (α-Al2O3) substrate with a vicinal-cut angle of α = 0.25° toward the a-plane $$\left( {11\overline{2} 0} \right)$$ on the quality of epitaxial ZnO films grown by metal organic chemical vapor deposition were studied. The atomic steps formed on sapphire substrate surface by annealing at high temperature were analyzed by atomic force microscopy (AFM). The annealing effects of sapphire substrate on the microstructural and optical properties of the ZnO films were examined by high-resolution X-ray diffraction, scanning electron microscopy, AFM and photoluminescence spectroscopy. Experimental results indicate that the film quality is strongly affected by annealing treatment of the sapphire substrate. X-ray diffraction study revealed that ZnO films deposited on c-plane sapphire substrate annealed at T ≥ 1050 °C exhibit a wurtzite phase and have a c-axis orientation. The decrease in FWHM for (0004) and $$\left( {10\overline{1} 4} \right)$$ ZnO peak confirms the improvement of the crystalline quality of ZnO thin film as increasing annealing substrate temperature. Sapphire annealing at 1100 °C for 3 h under oxygen prior to ZnO film growth is the best to achieve ZnO film with good structural and optical quality.

In this study, the epitaxial growth of ( 11 2 ¯ 0 ) (≡ a -plane) Zn (1− x ) Cd x O thin films on ( 01 1 ¯ 2 ) (≡ r -plane) sapphire substrates was performed by metal organic chemical deposition (MOCVD) with the same cadmium flow. The influence of growth temperature (850 °C≤ T g ≤950 °C) and position of sample in the MOCVD reactor on the microstructural and optical properties of Zn (1− x ) Cd x O thin films was investigated using high resolution X-ray diffraction (HRXRD), scanning electron microscopy (SEM), optical transmission measurements and photoluminescence spectroscopy (PL). A maximum Cadmium incorporation about 5.5% is obtained at T g =850 °C for the sample placed as a nearest reactor source. X-ray diffraction study revealed that all films had wurtzite phase and a -plane≡ ( 11 2 ¯ 0 ) film are epitaxially grown on r -plane sapphire. The near band-edge photoluminescence emission shifts gradually to lower energies as Cd is incorporated and reaches 3.10 eV for the highest Cd content (5.5%) at low temperature (2 K). The uniform striated morphology along the [0001] ZnO direction which is a typical feature observed in non-polar ZnO is lost with an increase in the Cd incorporation content. This morphology change is due to the crystal lattice deformation which is revealed by HRXRD.

International audience; The diffusion of excitons injected in ZnO/Zn 0.92 Mg 0.08 O quantum well heterostructures grown by metal-organic-vapor-phase-epitaxy on non-polar ZnO substrates is investigated at room temperature. Cathodoluminescence linescans in a field-emission-gun scanning-electronmicroscope are performed across cleaved cross-sections. A 55 nm diffusion length is assessed for excitons in bulk ZnMgO. When prepared as small angle bevels using focused ion beam (FIB), the effective diffusion length of excitons is shown to decrease down to 8 nm in the thinner part of the slab. This effect is attributed to non-radiative surface recombinations, with a 7 × 10 4 cm s−1 recombination velocity estimated at the FIB-machined ZnMgO surface. The strong reduction of the diffusion extent in such thin lamellae usually used for transmission electron microscopy could be use improve the spatial resolution of cathodoluminescence images, often limited by diffusion processes.

International audience; ZnO nanowires were grown on sapphire substrates using metalorganic chemical vapor deposition. The samples were subsequently annealed under zinc pressure in a vacuum-sealed ampoule, at temperature ranging from 500 to 800°C. The originality and the main motivation to provide a zinc-rich atmosphere were to prevent the out-diffusion of zinc from the nanowires. In doing so, the perfect structural properties and the morphology of the nanowires are kept. Interestingly, photoluminescence experiments performed on nanowires annealed in a narrow window of temperature [580-620°C] show a spectacular improvement of the optical quality, as transitions commonly observable in high quality bulk samples are found. In addition, the intensity of the so-called "surface excitons" (SX) is strongly decreased. To accurately investigate the chemical modifications of the surface, XPS experiments were carried out and show that zinc hydroxide species and/or Zn(OH)2 sublayer were partially removed from the surface. These results suggest that the annealing process in zinc vapor helps to properly reconstruct the surface of ZnO nanowires, and improves the optical quality of their core. Such a thermal treatment at moderate temperature should be beneficial to nanodevices involving surface reaction, e.g. gas sensors.

International audience; The control of the composition of mixed organic-inorganic hybrid perovskites by solid-state alloying is a very efficient tool to tune the band gap of the material, leading to enhanced optical performances. At this end, we have elaborated a series of mixed-halide two-dimensional hybrid perovskites (C6H11NH3)(2)[PbBr4-xIx], with 0 2), the photoluminescence spectra showed a sharp peak with a relatively small Stokes shift (less than 0.2 eV) attributed to free or bound excitons emissions. In contrast, when the bromide is majority (x < 2), the photoluminescence response consists in a broadband white-light emission with a very large Stokes shift (between 1.2 eV and 0.3 eV), attributed to self-trapped excitons activated by a strong structural distortion of the inorganic sheets. Confronting optical and structural data highlighted the effect of the structure in monitoring the optical properties, since the intensity of the white-light emission increases with the bromine content and was found to excellently correlate with the change of the angular distortion of inorganic octahedra PbX6 (X = I/Br)

Wurtzite ZnO thin films were prepared on sapphire substrate by metal organic chemical vapor deposition (MOCVD). Raman scattering studies on different crystallographic textures were performed in the backscattering geometry, and polarization effect is investigated in different configurations and . ZnO Raman modes are investigated in each texture. In the case of ZnO thin film deposed on r-() sapphire plane and using backscattering geometry, new Raman line was observed at 390 cm−1 because this mode has not been noticed in this geometry. It is shown that the frequencies of the quasi-phonon modes of the examined thin film are in good agreement with the theoretical values calculated within the framework of Loudon model. Copyright © 2014 John Wiley & Sons, Ltd.

An attempt to incorporate dopants in ZnO nanowires grown using metal organic chemical vapour deposition (MOCVD) on sapphire substrates is presented. Diffusion of phosphorus (P) and arsenic (As) into the ZnO nanowires and ZnO substrates were carried out in vacuum sealed ampoules at temperatures ranging from 580 to 800 °C. Doping sources were Zn3P2 or Zn3sA2. The evolution of the wires morphology shows a dramatic degradation above 620–650 °C. SIMS analysis reveals the transport of P and As onto the sample surface. Mass profiling shows that the dopants do not diffuse significantly into bulk ZnO. This is confirmed by both Raman scattering and low temperature photoluminescence (PL) where no optical signatures related to the incorporation of P or As are observed. Surprisingly, PL experiments performed on nanowires processed at a temperature where the effect of annealing on the morphology start to be visible show an improved quality, and features commonly observables in high quality bulk samples. These results suggest that defects localised at the surface of the ZnO nanowires could be removed using post-annealing in Zn rich atmosphere. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

ZnO/ZnSe core/shell nanowire arrays have been grown by metal-organic chemical vapor deposition on c-plane sapphire. The morphology and the structure of the nanostructures were characterized by scanning electron microscopy and transmission electron microscopy. They exhibit well-aligned core/shell ZnO/ZnSe nanowires with a good crystalline quality although some surface roughness is associated to the deposition of ZnSe on the lateral ZnO facets. X-ray diffraction combined with Raman spectroscopy and electron diffraction demonstrate that ZnO grows along the c-axis with the wurtzite (W) structure, but ZnSe can be deposited epitaxially in the zinc-blende (ZB) structure on the M-facet of the wires. Optical transmission measurements reveal an additional contribution at about 2.15 eV attributed to the type-II interfacial transition between the valence band of ZB-ZnSe and the conduction band of W-ZnO. These observations confirm the potential interest of ZnO/ZnSe core/shell nanostructures for photovoltaic applications.

Undoped ZnO films were deposited by atmospheric metal-organic chemical vapor deposition (MOCVD) on (0001) ZnO substrate. The films were grown at various partial pressure ratios of oxygen and zinc precursors (VI/II) using either N 2 or H 2 as carrier gas. Micro-Raman scattering was employed to study the effects of carrier gas, VI/II ratio and annealing on carbon impurity incorporation into the ZnO films. Besides the well known phonon modes of ZnO, Raman spectra of the samples grown with N 2 carrier gas show two additional broad peaks, which are ascribed to carbon sp 2 clusters related modes, spreading in the frequency range 1300–1600 cm −1 and dominate the Raman spectrum of the sample grown under oxygen deficiency (VI/II=0.25). In addition, a band centered at ∼520 cm −1 , considered as some defects related local vibrations, appears in the samples grown with N 2 as carrier gas and its intensity increases when the VI/II ratio decreases. The average cluster size, estimated from the intensity ratio of D over G bands of the carbon sp 2 clusters, ranges from 16.5 to 19.4 A. However, in all the samples grown with H 2 as carrier gas, the bands related to carbon sp 2 clusters and defects, are largely suppressed and the second-order-Raman scattering band (1050–1200 cm −1 ) is clearly observed in addition to the bulk ZnO lattice modes. After annealing the samples at 900 °C in oxygen ambient, the crystal quality has been improved for all the samples but the carbon related bands, formed in the as-deposited films grown with the N 2 carrier gas, were only weakened.

ZnO nanowires with different nitrogen concentrations were grown by metalorganic chemical vapour deposition (MOCVD) using DEZn, NO2 and NH3 as zinc, oxygen and nitrogen doping sources respectively. The NH3 concentration in the vapour phase varied from 0 to 13.8 μmol min−1 to favour the nitrogen incorporation. The ZnO nanowires were characterised by scanning electron microscopy, photoluminescence and micro-Raman spectroscopy. Two additional intense Raman peaks at 272 and 580 cm−1 are found to be related to the nitrogen incorporation. Micro-Raman scattering of a single nanowire probes the uniformity of the nitrogen concentration along the nanowire for highly doped samples. The photoluminescence (PL) spectra exhibit donor–acceptor pair band which confirms the incorporation of the nitrogen in the ZnO nanowires.

International audience; In this work, phosphorus donors in diamond have been investigated by means of Fourier Transform Infra-Red (FTIR) transmission spectroscopy on a series of fully-characterized homoepitaxial layers. Low-temperature FTIR absorption spectra have been obtained for concentrations of donors in the range ND = 3.7 × 1016– 3.5 × 1018 cm− 3 and compensating acceptor impurities in the range NA = 2.3 × 1016– 3.0 × 1018 cm− 3. The absorption spectra is shown to exhibit two peaks at 4220 cm− 1 and 4540 cm− 1 corresponding to electronic transitions from the ground state to the 2p0 and 2p± excited states, respectively, of phosphorus donors in the neutral state of charge. The intensity of the most intense peak at 4540 cm− 1 is found proportional to ND-NA over two decades. The absorption cross-section of the corresponding transition is deduced providing a calibration law for the determination of ND-NA in phosphorus-doped diamond. Furthermore, the linewidth of the peak exhibits a linear variation with the compensating acceptor concentration, interpreted as the effect of the distribution of ionized impurities. The use of the non-destructive and contact-less FTIR optical method is finally discussed to determine the compensation ratio in phosphorus-doped diamond.

International audience; ZnO-ZnSe core-shell nanowires have been grown by metal organic chemical vapor deposition and subsequently annealed in an O2 atmosphere. It has been found that the incorporation of oxygen into the ZnSe shell over the 470–580 °C temperature range results in a phase transformation from zinc Blende to orthorhombic and wurtzite. The X-ray diffraction pattern confirms that the heterostructures are composed of a wurtzite ZnO core and an oxide ZnSeO shell. The Raman spectroscopy study shows the appearance of additional peaks at 220 cm−1, 278 cm−1, 480 cm−1, 550 cm−1, and 568 cm−1, which reveal a phase transformation associated with the incorporation of the oxygen into the shell after annealing at 470 °C. This work opens a way to study the structure stability of ZnO-ZnSe core-shell nanowire production and help to understand the mechanisms of the oxidation in ZnO-ZnSe core-shell nanowires.

We present Raman scattering study of wurtzite ZnO nanowires deposited by metal–organic chemical vapor deposition (MOCVD) on (0001) sapphire. It is shown that the misorientation of the nanowires, i.e. the inclination with respect to the vertical direction, mixes A1 and E1 Raman modes, giving rise to new modes for which the propagation directions make various angles with the C-axis of ZnO nanowires. Two particular bands depending on the tilt of the nanowires are observed at 400 and 585 cm−1. They are attributed to TO and LO quasi-phonons, and explained using Loudon's model. Morphological information of the nanowires was extracted and an average orientation of nanowires is calculated.

Correlations between photoluminescence and temperature-dependent Hall measurements were carried out on unintentionally doped HgCdTe epilayers with cadmium composition of 32.7%. These films were grown by liquid-phase epitaxy and post-annealed under different conditions as follows: a p-type annealing was used to control the mercury vacancy concentration, and an n-type annealing under saturated mercury atmosphere was used to fill the mercury vacancies. Comparison of the results obtained by these two characterization techniques allowed us to identify the two acceptor energy levels of the mercury vacancy. Moreover, the “U-negativity” of the vacancy was evidenced: the ionized state V− is stabilized under the neutral state V0 by the dominance of the Jahn–Teller effect over Coulombic repulsion. Finally, three epilayers with different cadmium compositions were also characterized to complete this study.

ZnO thin films were grown by metalorganic chemical vapor deposition on (0001) Zn- and O-polar surfaces of ZnO substrate. The surface morphology of these films was investigated by micro-Raman scattering and scanning electron microscopy. In the case of Zinc-polar face and using back scattering configuration, two new Raman bands were observed at 398 and 584.5 cm−1. They have been interpreted as quasi phonons TO (qTO) and LO (qLO) respectively. The origin of these modes was attributed to the particular morphology of ZnO films grown on Zn-polar face, which consists in c -axis nano-platelets, randomly tilted from the substrate. qTO and qLO frequencies have been calculated using the model of Loudon. SEM observation is in agreement with our Raman interpretation.

Nanowires with different nitrogen concentrations were grown by Metal-Organic Chemical Vapor Deposition (MOCVD) using DEZn, N2O and NH3as zinc, oxygen and nitrogen doping sources respectively. Low temperature photoluminescence, Raman spectroscopy and Transmission Electron Microscopy are combined to study the incorporation of nitrogen in the wires. The observation of donor-acceptor pair band confirms that the incorporation nitrogen in ZnO nanowires is responsible for the creation of acceptor centers. The additional peaks observed in Raman are correlated to nano-sized inter-atomic distance fluctuations observed in TEM. These domains combined with a resonance effect are probably the explanation of the huge Raman cross section observed for the impurity related peaks.

In this work, we present a detailed Raman scattering study to clarify the origin of the mode at 379 cm−1 which is observed in Raman spectra of the ZnO films grown on c-sapphire substrates and generally attributed to the A1-transverse optical (A1-TO) mode of ZnO. The studied ZnO films were deposited by metal-organic chemical vapor deposition on c-sapphire and (0001) ZnO substrates. In the z(−,−)z backscattering configuration, the A1-TO mode is forbidden, while the 379 cm−1 peak is still observed in the as-deposited film grown on sapphire substrate. However, this mode is not observed in Raman spectra of the as deposited film grown on ZnO substrate. We suggest that the peak at 379 cm−1 is the E1g mode of the sapphire substrate which is allowed in z(−,−)z backscattering configuration. The effects of annealing, the substrate and the collection cross-section on Raman active modes were analyzed. Copyright © 2011 John Wiley & Sons, Ltd.

Nitrogen was incorporated into ZnO films grown by metalorganic chemical vapour deposition (MOCVD) on ZnO substrates using DMZn-TEN, tert-butanol and diallylamine, respectively, as zinc, oxygen and doping sources. The carrier gas was either hydrogen or nitrogen and the partial pressure ratio (RVI/II) was varied in order to favor the nitrogen incorporation and/or reduce carbon related defects. The ZnO films have been characterized by Micro-Raman scattering and SIMS measurements. SIMS measurements confirm the nitrogen incorporation with concentrations extending from ∼1019 cm−3 to ∼4×1020 cm−3. Raman spectra show nitrogen local vibration modes in films grown at low RVI/II ratio and using H2 as carrier gas. However, a vibration band attributed to carbon clusters dominates the Raman spectra for films grown with N2 carrier. The contribution of N complexes was discussed. The strain was calculated for the as-grown and annealed films and it changes from tensile to compressive after annealing.

Nitrogen- and antimony-doped thin layers have been grown by metal organic vapour phase epitaxy (MOVPE) at 950 °C. The nitrogen- and antimony-doped layers have been characterized by Raman scattering and photoluminescence (PL) spectroscopy. In nitrogen-doped layers, we have observed several Raman lines from local vibrational modes related to nitrogen. Low temperature PL spectra exhibit donor-acceptor pair (DAP) transitions on both nitrogen- and antimony-doped layers. The DAP transitions have been analysed versus temperature and excitation power experiments. The acceptor binding energy of antimony in ZnO is evaluated to 200 meV.

Various one-dimensional (1D) ZnO-based nanostructures, including ZnO nano-wires (NWs) grown using vapour-liquid-solid (VLS) process, ZnO/ZnSe core/shell, nitrogen-doped ZnO and ZnMgO NWs were grown by metalorganic chemical vapour deposition (MOCVD). Transmission electron microscopy (TEM) analysis is presented. For all the samples, a high crystalline quality is observed. Some features are emphasized such as the gold contamination of ZnO wires grown under the metal droplets in the VLS process. It is concluded that MOCVD is a suitable technique for the realization of original ZnO nanodevices.

ZnO and ZnO:Sb films were deposited using low pressure metal organic chemical vapor deposition on C- and R-oriented sapphire and O-polar ZnO substrates. Surface morphologies were studied using scanning electron microscopy. Whereas ZnO films grown on C-sapphire show a rough surface and hexagonal rods, the doped ZnO:Sb layers exhibit a relatively smoother surface, indicating a possible surfactant effect of antimony. The secondary ion mass spectrometry measurements permit to determine the antimony profile in the doped layers. Sb concentrations from 10 18 to 10 20 at/cm 3 were measured, depending on the growth conditions and substrate nature. Photoluminescence spectra exhibit donor-acceptor pair emission at 3.22 eV.

We studied the photoluminescence of Hg1−xCdxTe (x ≈ 0.3) layers grown by molecular-beam epitaxy on CdZnTe. The investigations were carried out on unintentionally doped, In-doped, and As-doped samples, and the effect of different annealing procedures was examined. Excitation-power-dependent and temperature-dependent comparative studies were performed. The transition mechanisms are discussed, and optical signatures for arsenic site transfer are found. The contributions due to As2Te3, As in an amphoteric site, Hg vacancies, and AsHg complexes were identified, and their ionization energies measured. The results are consistent with results found by other techniques. Thus, it is shown that photoluminescence applied to Hg1−xCdxTe can resolve characteristics corresponding to native and intentional donors/acceptors, and offers a nondestructive, fast tool for material characterization.

Metal organic vapor phase epitaxy (MOVPE) has been used to grow ternary Zn 1− x Mg x O layers on c-plane sapphire substrates. The precursors nitrous oxide, bismethylcyclopentadienyl magnesium, and dimethylzinc-triethylamine were used as the oxygen, magnesium, and zinc sources, respectively. Nitrogen was the carrier gas. The concentration of magnesium in the gas phase was varied, relative to the zinc concentration, by adjusting the partial pressures ratio R II =P Mg /(P Mg +P Zn ). Both R II and substrate temperature variations induce a strong dependence of the growth rate, structural and optical qualities, and magnesium content in the grown layer. When the R II ratio is increased from 0 to 0.8 at different substrate temperatures, the following are clearly observed: (i) a decrease of the growth rate, (ii) a shift of the Zn 1− x Mg x O (0 0 2) X-ray diffraction peak to higher diffraction angles from 34.44° (wurtzite ZnO) up to 34.63°, and (iii) a shift of the PL-near band edge emission from 3.36 eV (ZnO bandgap) up to 3.75 eV. This latter value corresponds to a magnesium concentration in the Zn 1− x Mg x O solid solution of approximately 20%.

The electrical properties in iron-passivated porous silicon (PS:Fe) with stable optical properties were studied. Iron is incorporated in porous silicon (PS) by impregnation method using Fe(NO 3 ) 3 aqueous solution. Energy dispersive X-ray analysis and Raman scattering revealed the presence of iron atoms over most of the PS layer surface. We discussed the current–voltage ( I – V ) of PS and PS:Fe structures under both forward and reverse bias conditions. The I – V measurements obtained on PS:Fe showed a rectifying effect and an improvement of both the threshold voltage and current intensity as compared with those relative to PS. By using the Richardson–Schottky diode equation and taking into account a series resistance ( R S ), all the parameters of the structures are determined and discussed. The presence of the iron in the PS matrix reduces the value of ideality factor n (close to 2) and the series resistance. At low voltage, the PS:Fe produces an important change in the transport mechanism of the PS; from ohmic to space charge limited conduction (SCLC) mechanism. The obtained results indicate the presence of the shallow acceptor levels in the gap due to the iron, allowing us to propose a band-gap diagram of Ag/PS:Fe/c-Si.

Metal organic vapour phase epitaxy (MOVPE) has been used to successfully grow one-dimensional (1D) ZnO deposits on (0 0 0 1)-ZnO substrate. Dimethylzinc–triethylamine and nitrous oxide were used as zinc and oxygen sources, respectively, with nitrogen as the carrier gas. Vertically aligned 1D ZnO structures were observed along the c-axis by using lower VI/II mole ratio RVI/II 800 °C). The diameter, length, density and the mechanism of formation could be controlled with the growth time. Scanning electron microscopy (SEM) shows different structures, i.e., sharp-top, flat-top and open-top with slim bottom and large-top one-dimensional ZnO. A good structural quality was revealed by X-ray diffraction rocking curve with a full-width at half-maximum (FWHM) varying from 40 to 92 arcsec with increasing growth time.