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International audience; In this paper, we study the internal quantum efficiency and lasing threshold of AlGaN/GaN separate confinement heterostructures designed for ultraviolet laser emission. We discuss the effect of carrier localization and carrier diffusion on the optical performance. The implementation of graded index separate confinement heterostructures results in an improved carrier collection at the multi-quantum well, which facilitates population inversion and reduces the lasing threshold. However, this improvement is not correlated with the internal quantum efficiency of the spontaneous emission. We show that carrier localization at alloy inhomogeneities results in an enhancement of the radiative efficiency but does not reduce the laser threshold, which is more sensitive to the carrier injection efficiency.

Here, we present the design and fabrication of AlGaN/GaN heterostructures that constitute the active element of electron-beam pumped UV lasers. The design of multi-quantum-well separate confinement heterostructures (SCHs) and graded-index separate confinement heterostructures (GRINSCHs) was adapted based on Monte Carlo simulations of the electron penetration depth. The structures were synthesized by plasma-assisted molecular beam epitaxy on bulk GaN substrates, and validated using transmission electron microscopy and X-ray diffraction. Mirror facets were fabricated by cleaving. Cathodoluminescence studies prove the benefits of the GRINSCH design in terms of carrier collection efficiency. The threshold power density under optical pumping with an Nd-YAG laser (266 nm) was below 200 kW/cm2 at room temperature.

International audience; We present a study of undoped AlGaN/GaN separate confinement heterostructures designed to operate as electron beam pumped ultraviolet lasers. We discuss the effect of spontaneous and piezoelectric polarization on carrier diffusion, comparing the results of cathodoluminescence with electronic simulations of the band structure and Monte Carlo calculations of the electron trajectories. Carrier collection is significantly improved using an asymmetric graded-index separate confinement heterostructure (GRINSCH). The graded layers avoid potential barriers induced by polarization differences in the heterostructure and serve as strain transition buffers which reduce the mosaicity of the active region and the linewidth of spontaneous emission.

Optical properties of ZnO nanorods (NRs) grown by vapour-liquid-solid (VLS) technique on 4H-p-SiC substrates were probed by cathodoluminescence (CL) measurements at room temperature and at 5 K complemented with electroluminescence. At room temperature the CL spectra for defect related emission intensity was enhanced with the electron beam penetration depth. We observed a variation in defect related green emission along the nanorod axis. This indicates a relatively poor structural quality near the interface between ZnO NRs and p-SiC substrate. We associate the green emission with oxygen vacancies. Analysis of the low-temperature (5 K) emission spectra in the UV region suggests that the synthesized nanorods contain shallow donors and acceptors. Original Publication:Nargis Bano, I Hussain, Omer Nour, Magnus Willander, Qamar Ul Wahab, Anne Henry, H S Kwack, D Le Si Dang, Depth-resolved cathodoluminescence study of zinc oxide nanorods catalytically grown on p-type 4H-SiC, 2010, JOURNAL OF LUMINESCENCE, (130), 6, 963-968.http://dx.doi.org/10.1016/j.jlumin.2010.01.006Copyright: Elsevier Science B.V., Amsterdam.http://www.elsevier.com/

High quality vertically aligned ZnO nanorods (NRs) were grown by low-temperature aqueous chemical technique on 4H-n-SiC substrates. Schottky light-emitting diodes (LEDs) were fabricated. The current-voltage (I–V) characteristics of Schottky diodes reveal good rectifying behavior. Optical properties of the ZnO nanorods (NRs) were probed by cathodoluminescence (CL) measurements at room temperature complemented with electroluminescence (EL). The room-temperature CL spectra of the ZnO NRs exhibit near band edge (NBE) emission as well as strong deep level emission (DLE) centered at 690 nm. At room temperature the CL spectra intensity of the DLE was enhanced with the increase of the electron beam penetration depth due to the increase of defect concentration at the interface and due to the conversion of self-absorbed UV emission. We observed a variation in the DLE along the nanorod depth. This indicates a relatively lower structural quality near the interface between ZnO NRs and n-SiC substrate. The room-temperature CL spectra of SiC show very weak emission, which confirms that most of the DLE is originating from the ZnO NRs, and SiC has a minute contribution to the emission.

Vertically aligned ZnO nanorods (NRs) with a diameter in the range of 160-200 nm were grown on p-GaN/sapphire substrates by aqueous chemical growth technique and white light emitting I diodes (LEDs ...

Optical properties of ZnO-based single nanorods are probed by cathodoluminescence (CL) measurements at T = 5 K. We observe a variation of the ZnO near band edge CL by three orders of magnitude along the nanorod axis, accompanied by a spectral blueshift of 10-30 meV. This indicates a rather poor structural quality of the nanorod bottom part, close to the substrate. ZnO/ZnMgO quantum wells grown on top of ZnO nanorods are found to exhibit much stronger confinement effects as compared to their two-dimensional counterparts, suggesting a reduced spontaneous and piezoelectric polarization effects.

The quantum plasmonics field has emerged and been growing increasingly, including study of single emitter-light coupling using plasmonic system and scalable quantum plasmonic circuit. This offers opportunity for the quantum control of light with compact device footprint. However, coupling of a single emitter to highly localized plasmonic mode with nanoscale precision remains an important challenge. Today, the spatial overlap between metallic structure and single emitter mostly relies either on chance or on advanced nanopositioning control. Here, we demonstrate deterministic coupling between three-dimensionally nanofocused plasmonic modes and single quantum dots (QDs) without any positioning for single QDs. By depositing a thin silver layer on a site-controlled pyramid QD wafer, three-dimensional plasmonic nanofocusing on each QD at the pyramid apex is geometrically achieved through the silver-coated pyramid facets. Enhancement of the QD spontaneous emission rate as high as 22 ± 16 is measured for all processed QDs emitting over ∼150-meV spectral range. This approach could apply to high fabrication yield on-chip devices for wide application fields, e.g., high-efficiency light-emitting devices and quantum information processing.

In recent years, the nanorod technology has emerged as a very promising alternative to high efficiency optoelectronics devices. In this chapter, we discuss potential advantages of the one-dimensional geometry as compared to its planar counterpart for solid-state lighting. We review recent progress in growth by metal-organic vapor phase epitaxy of core-shell InGaN multi-quantum-well heterostructures, and their nano-characterization through cross correlation analysis of structural, optical, transport, and electrical measurements.

We present a study of the effect of Si doping localization on the optical and structural properties of GaN/AlN multiple-quantum-well structures for intersubband (ISB) absorption at 1.55 μm. Samples were either undoped or Si doped in different regions (barrier, quantum well (QW), middle of barrier or middle of QW). Structural characterization by atomic force microscopy and X-ray diffraction does not show significant differences in the crystalline quality. All doped samples present room-temperature p-polarized ISB absorption of about 1%–2% per pass, with a line width of 80–90 meV. In contrast, undoped samples present a weaker ISB absorption with a record line width of 40 meV. Both photoluminescence (PL) and ISB absorption display structured shapes whose main peaks correspond to monolayer fluctuations of the well thickness. The emission and absorption line widths depend on the Si doping concentration, but not on the Si location.

We study the self organized growth of GaN quantum dots deposited by molecular beam epitaxy on Al x Ga 1-x N, with x varying between 1 and 0.21. As a result of the specific strain relaxation mechanism of Al x Ga 1-x N on AlN, it is found that dots can be formed for an Al content as low as about 30%. Monopolar devices have been realized by depositing Schottky contacts on n-type doped Al 0.5 Ga 0.5 N. Finally, electroluminescence of Eu-doped GaN quantum dots embedded in n-type Al 0.5 Ga 0.5 N has been demonstrated, emphasizing the potentialities of such an active layer for room temperature visible light emission.

We report on the growth of Tb-doped GaN quantum dots deposited by plasma-assisted molecular beam epitaxy. It was found that Tb ions enhance the desorption process of Ga ad-atom on the growing surface. This effect becomes more important with increasing growth temperature, and above a certain amount of Tb, the QDs formation is completely inhibited. Transitions from the 5D4 excited state were found intense and temperature stable, while the transitions from 5D3 excited state were only observed at low temperature. A comparative optical study with Tb-doped AlN thick layer indicates that Tb ions are incorporated in GaN QDs. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of stacking on the optical properties of self-organized GaN/AlN quantum dots (QDs) grown by plasma-assisted molecular beam epitaxy was investigated by photoluminescence (PL), PL excitation (PLE), and cathodoluminescence (CL) spectroscopic techniques. With an increase in the number of the GaN QDs stacking layer, we observed a red shift in the main QD PL peaks. A Stokes-like shift was observed between PL emission and PLE absorption edge for all the samples. From the depth-resolved CL of a 200-period GaN QD sample, we observed that the main QD CL emission peak energy position does not change much, while the higher-energy side CL peak around ∼3.7 eV shows a variation of its peak position with the accelerating voltage probably due to the change in either distribution of QD size/shape or wetting layer properties during the growth of multiple stacking of GaN QDs. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on a comparative optical study of molecular beam epitaxy grown GaN:Eu quantum dots (QDs) and GaN:Eu layer. In the GaN:Eu layer the narrow emission lines of the 5D0-7F2 transition allow to identify two different Eu locations corresponding to near the sample surface and lying deeper in the bulk. Eu3+ emission from QDs has been found to be at the same spectral position than that assigned to Eu3+ ions located in the bulk of the GaN:Eu layer. Eu emission in the temperature range 4-300 K is thermally stable in doped QDs, but exhibits a strong thermal quenching in the doped layer, particularly for Eu3+ ions located near the surface. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on the controlled growth of Si doped GaN/AIN quantum dot (QD) superlattices, in order to tailor their intersubband absorption within the 1.3-1.5 μm telecommunication wavelengths. The QD size is tuned by modifying the amount of GaN in the QDs and the growth temperature. Silicon can be incorporated in the QDs to populate the first electronic level, without significant perturbation of the QD morphology. As a proof of the capability of these structures for infrared detection, a quantum-dot intersubband photodetector at 1.38 μm with lateral carrier transport is demonstrated.

We report on a comparative optical study of InGaN:Eu quantum dots (QDs) and GaN:Eu layer grown by molecular beam epitaxy (MBE). Analysis of the 5D0 → 7F2 transition as a function of the excitation wavelength shows that Eu3+ ions in InGaN:Eu QDs are located inside InGaN QDs and also in the GaN barrier layer. The existence of Eu3+ ions in the GaN barrier layer is explained by Eu segregation/diffusion during growth. For Eu3+ ions located inside InGaN QDs the photoluminescence (PL) shows only a slight decrease with temperature from 5 K to 300 K. In contrast, the PL from Eu3+ ions in the GaN barrier layer or in GaN thick layer shows a much more pronounced thermal quenching.

We report on the MBE growth of GaN and InGaN quantum dots (QDs) doped with rare earth ions, namely Eu, Tm and Tb exhibiting red, blue and green luminescence, respectively. Intense photoluminescence/cathodoluminescence is observed, resulting from the spatial localization of rare earth ions in dots combined with the confinement properties of the carriers. White light emission has been produced by combining the three rare earths in a multilayer sample of stacked GaN QD planes. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present new growth conditions for growing high-quality CdSe/ZnSe quantum dots with photoluminescence emission measurable up to room temperature. The surface morphology is characterized in situ by Reflective High Energy Electron Diffraction (RHEED). The key point is the introduction of a new step in the growth process using amorphous selenium to induce a 2D–3D transition of a CdSe strained layer on ZnSe to form the dots. Optical characterizations by photoluminescence of CdSe/ZnSe quantum dots obtained that way, as well as X-ray diffraction results are also discussed here.

We demonstrate Eu, Tm and Er doping of GaN quantum dots. In Er-doped samples, two very sharp blue lines were observed. These lines were dominant over the green lines reported in the case of Er-doped GaN thick layers. However, intensities were very low in comparison with Eu-doped and Tm-doped GaN QDs. Intense blue emission from Tm-doped GaN QDs was observed. Temperature-dependent photoluminescence was studied, and the intensity only decreased to 27% between room temperature and 10 K. Structural studies on Tm-doped samples showed that the kinetic role of Tm atoms was different from that of Eu atoms.

We have studied the structural and optical properties of GaN quantum dots (QDs) doped with Tm and Eu. It has been found that the morphology of the dots was affected by the presence of the rare earth atoms. Differences in incorporation have also been pointed out, Eu being located inside the QDs while Tm is more likely to be found at the interface between GaN QDs and AlN matrix. Intense and sharp Eu- and Tm-related transition lines are observed in the photoluminescence and cathodoluminescence spectra of doped QDs, with no thermal quenching between 20 and 300 K. They exhibit a saturation effect with increasing excitation power, independently of the temperature. It is tentatively proposed that some transition lines in GaN:Tm QDs could be induced by the presence of the internal electric field.

Two monolayers of CdSe sandwiched by ZnSe layers were grown by molecular-beam epitaxy on a vicinal GaAs surface substrate. Small ensembles of these self-assembled quantum dots (QD) have been studied at low temperatures using micro-photoluminescence spectroscopy. We observe reversible spectral diffusion in individual QD luminescence lines. The energy shift is negligibly small at low optical excitation power and amount to about 0.7 meV under higher excitation (0.6 kW/cm2). Because the energy shift is found to be significantly smaller than the exciton–biexciton splitting of CdSe QDs even under high excitation, the conventional spectral filtering could be used to effectively select the exciton-related emission from these QDs.

In this paper we present experimental and theoretical study of intersubband transitions at telecommunication wavelengths in GaN/AlN quantum wells grown by molecular beam epitaxy on sapphire substrates. Crossed Rutherford back-scattering and photoluminescence experiments show that strong in-plane carrier localization occurs due to thickness fluctuations at GaN/AlN interfaces. Fourier transform infrared spectroscopy and photo-induced absorption spectroscopy performed on doped and undoped samples reveal a systematic blue-shift of the e1–e2 transition due to many body interactions. A good agreement is achieved between experiment and self-consistent Schrodinger–Poisson calculations. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We demonstrate the growth of GaN quantum dots doped with Eu by plasma-assisted MBE. Intense emission from the intra-atomic 4f transition of Eu3+ was observed at 622 nm. GaN quantum dots (QDs) doped with 1% Eu showed the maximum emission. The full-width at half maximum (FWHM) of the CL spectrum of Eu-doped GaN QDs was 2.1 nm at room temperature. Eu doping increased the size of QDs by 4 times and decreased the density of QDs by one order of magnitude. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

GaN/AlN quantum dots grown by molecular beam epitaxy either on silicon (111), sapphire or 6H-SiC (0001) substrate have been investigated using photoluminescence, cathodoluminescence, Fourier transform infrared spectroscopy and attenuated total reflection spectroscopy. In-plane polarized intraband absorption is observed at energies of similar to 150 and 310 meV in GaN dots with 22 and 7.5 nm base diameter, respectively. For bigger dots, we observe three interlevel absorptions with a polarization component along the c-axis at energies ranging from 0.52 to 0.97 eV. Based on a simple 2D modelling of the confinement energies we show that the resonant absorptions involve conduction-band interlevel transitions between the electron ground state and states with one or two nodes along the c-axis and that in large dots, the internal field governs the transition energies. (C) 2002 Elsevier Science B.V. All rights reserved.

We have fabricated CdMgTe/CdMnTe based pillar microcavities with diameters down to 2 μm by optical lithography and reactive ion etching. Three-dimensional optical confinement is demonstrated by the occurrence of higher lateral modes. In the high excitation regime, the emission linewidth in pillar microcavities is found to be significantly reduced as compared to planar microcavities.

A report is presented on the fabrication of light emitting diodes (LEDs) based on GaN core/shell wires on conductive substrates by metal organic vapour phase epitaxy. Catalyst-free GaN-based wires are grown spontaneously on 2-inch n-doped silicon substrates without any thick buffer layer. The LED wire heterostructure consists of an n-type GaN:Si core covered radially by five InGaN/GaN quantum wells and a p-type GaN:Mg shell. Macroscopic devices that integrate around 10 6 wire-LEDs have been obtained thanks to a simple, direct and full-wafer scale contacting process. For the first time, continuous-wave electrical injection at room temperature through the Si substrate into a cm 2 -chip of GaN-based core/shell wire-LEDs is successfully demonstrated, producing blue electroluminescent emission at 450 nm.

We report on the identification of an optimum deposited amount of AlGaN in AlGaN/AlN quantum dot (QD) superlattices grown by molecular-beam epitaxy, which grants maximum luminescence at room temperature by finding a compromise between the designs providing maximum internal quantum efficiency (60%) and maximum QD density (9.0 × 1011 cm−2). The average Al composition in the QDs is estimated at 10.6% ± 0.8% by combining x-ray diffraction measurements with three-dimensional calculations of the strain distribution. The effect of the variation of the QD height/base-diameter ratio on the interband and intraband optical properties was explored by fitting the experimental data with three-dimensional calculations of the band diagram and quantum confined states.

International audience; We report on the realization of monolithic, i.e. fully epitaxial ZnSe-based microcavities with a 1λ-cavity and a 3λ-cavity for the investigation of strong coupling phenomena. A crucial building block is the fabrication of a lattice matched distributed Bragg reflector for the blue spectral region, consisting of quaternary ZnMgSSe layers as the high-index material and a MgS/ZnCdSe superlattice as the low-index material. Strong coupling at low temperatures was achieved with a vacuum Rabi splitting of 19 meV for the 1λ-cavity (at 70K) and of 40 meV for the 3λ-cavity (at 7 K).Microstructures such as micropillars, waveguides, ringresonators, and molecule chains were fabricated using focused ion-beam etching. Discrete optical modes in micropillars were observed for both cavity lengths confirming three-dimensional optical confinement. Q-factors up to 6500 indicate a high optical quality.

International audience; The AlGa intermixing at Al(Ga)N/GaN interfaces in nanowires and the chemical inhomogeneity in Al x Ga 1-x N/AlN nanodisks (NDs) are attributed to the strain relaxation process. This interpretation is supported by the three-dimensional strain distribution calculated by minimizing the elastic energy in the structure. The alloy inhomogeneity increases with Al content, leading to enhanced carrier localization signatures in their optical characteristics i.e. red shift of the emission, s-shaped temperature dependence and linewidth broadening. Despite these alloy fluctuations, the emission energy of AlGaN/AlN NDs can be tuned in the 240-350 nm range with internal quantum efficiencies around 30%.

We studied and improved gallium nitride (GaN) nanowire (NW) based light emitting diodes (LEDs). PIN nanodiodes with and without InGaN/GaN multiple quantum wells (MQWs) were grown by molecular beam epitaxy (MBE) under N-rich conditions on n-doped Si(111) substrates. Thanks to the coalescence of the p-type region of the NWs grown at low temperature, an autoplanarization process has been performed to obtain LEDs. Ni/Au top contacts have been deposited and patterned in order to bias the devices. A multiple-scale characterization approach has been carried out through the comparison of localized cathodoluminescence (CL) and macroscopic electroluminescence (EL) spectra. It shows that the EL emission of PIN-based LED at room temperature is related to defects in the p-type region of the NWs. In order to enhance the radiative recombinations of NW-based LEDs, we have first added InGaN/GaN MQWs, and secondly an electron blocking layer (EBL) has been inserted between the MQWs and the p-type zone of the NWs. The LED with EBL exhibited an emission band at 420 nm. The blue-shift of this emission band with increasing injected current is attributed to quantum confined Stark effect (QCSE) and evidences the radiative emission of InGaN/GaN MQWs. At 50 mA dc current, this improved NW-based LED emits about 500 times more light than the heterostructure without EBL. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

In this work we report on the fabrication and characterization of a n-ZnO/p-GaN heterojunction LED. The p-GaN layer was fabricated using MOCVD on Al2O3 with Mg as the acceptor whereas the ZnO nanostructures were grown in a very simple vapor transport system without any additionally doping. Room temperature electroluminescence (EL) measurements show green deep band emission centered at 2.3 eV which is clearly visible with the naked eye when the structure is forward biased. Cathodoluminescence mapping was performed to explain the absence of the band edge emission in the EL spectrum. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on the growth, structural and optical properties of GaN/AlN free standing NWs. The NW lateral growth rate was investigated using thin AlN marker layers. The lateral growth is found to be homogeneous along the NW axis. Its rate can be tuned from ∼1% to ∼10% of the axial growth rate by changing III/V flux ratio. The resulting axial and lateral heterostructures were studied by micro-photoluminescence and micro-cathodoluminescence, which revealed sharp (several meV broad) emission lines. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present a new method, using amorphous selenium, for inducing a well-controlled 2D–3D transition of a strained CdSe/ZnSe layer, i.e. for initiating self-organization of CdSe quantum dots that does not occur spontaneously during epitaxial growth. X-ray diffraction results evidence the very good crystal quality of the samples obtained using this technique. Optical characterizations by photoluminescence and time-resolved photoluminescence show the interest of this process in the growth of CdSe/ZnSe quantum dots.

We report on the growth and properties of two types of AlGaN/AlN nanostructures: Stranski-Krastanow quantum dots (SK-QDs) and nanodisks (NDs) created by nanowire heterostructuring. In both cases, the emission wavelength can be tuned in the range of 240-350 nm at room temperature by varying the flux ratio and the nominal amount of AlGaN in the nanostructures. The efficient carrier confinement in these nanostructures leads to an internal quantum efficiency around 0.5. However, the emission spectra of AlGaN/AlN NDs show broader linewidth than those of SK-QDs, which is attributed to inhomogeneities in height and in chemical composition. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report on the structural and optical properties of AlGaN/AlN quantum dot (QD) superlattices synthesized by plasma-assisted molecular-beam epitaxy. Modifying the composition and geometry of the QDs, the peak emission wavelength can be shifted from 320 nm to 235 nm while keeping the internal quantum efficiency larger than 30%. The efficient carrier confinement is confirmed by the stability of the photoluminescence (PL) intensity and decay time, from low temperature up to 100 K. Above this threshold, the PL intensity decreases and the radiative lifetime increases due to carrier thermalization. We also identified the intraband electronic transition between the ground level of the conduction band and the first excited state confined along the growth axis (s-pz).

Optical pumping has been used to investigate gain mechanisms in CdTe/CdMnTe multi-quantum-well GRINSCH lasers. Lasing action has been obtained at room temperature for excitations as low as 3 kW/cm 2 , e.g. well below the critical density for the transition to an electron-hole plasma. Effects of temperature and cavity length on the stimulated emission are found to be consistent with the model of excitonic gain in an inhomogeneously broadened system proposed by Ding et al.

The growth of CdMnTe by molecular‐beam epitaxy is described, including an in situ calibration of alloy composition by reflection high‐energy electron diffraction intensity oscillation, which takes advantage of the larger sticking coefficient of Mn with respect to Cd. Layers are studied by photoluminescence, x‐ray diffraction, transmission electron microscopy, and cathodoluminescence imaging. Relaxation of the mismatch strain occurs through different mechanisms, depending on the sign and magnitude of the mismatch. Once identified the characteristic features of the cathodoluminescence images are used to determine the critical thickness of layers of uniform composition or of more elaborate heterostructures. A heuristic criterion for the relaxation of mismatch strain in heterostructures incorporating layers of continuously varying composition is checked.

We report on room temperature photorefractive properties of CdTe/CdZnTe quantum wells. The device works as a distributed Self Electro-optic Effect device based on a Schottky diode and optical modulation of the excitonic absorption in the CdTe/CdZnTe quantum wells.

We report experimental and theoretical results on interband and intersubband transitions in GaN quantum wells with strained AlN barriers. All of the samples are grown by molecular-beam epitaxy on sapphire (0001) substrates. The results show that even at room temperature, strong electron localization occurs in the plane of the quantum wells due to the combined effect of monolayer thickness fluctuations and the high internal field in the GaN layers. We also demonstrate that the intersubband absorption is systematically blueshifted in n-doped quantum wells with respect to nominally undoped samples as a result of strong many-body effects, namely the exchange interaction. The results for both undoped and doped quantum wells are in good agreement with simulations.

We investigated the optical properties of two monolayers of CdSe sandwiched by ZnSe layers grown by molecular-beam epitaxy on GaAs substrates with a vicinal tilt of 2° in the [111] direction. By varying the spatial resolution from 10 μm down to 500 nm, sharp photoluminescence lines due to the recombination of excitons confined into quantum dots could be observed at low temperature. The dot density could be as low as ≈109 dots/cm2, which is smaller than previously reported values by at least one order of magnitude.

Excitonic phenomena, such as excitonic absorption and emission, have been used in many photonic and optoelectronic semiconductor device applications. As the sizes of these nanoscale materials have approached to exciton diffusion lengths in semiconductors, a fundamental understanding of exciton transport in semiconductors has become imperative. We present exciton transport in a single MgZnO nanorod in the spatiotemporal regime with several nanometer-scale spatial resolution and several tens of picosecond temporal resolution. This study was performed using temperature-dependent cathodoluminescence and time-resolved photoluminescence spectroscopies. The exciton diffusion length in the MgZnO nanorod decreased from 100 to 70 nm with increasing temperature in the range of 5 and 80 K. The results obtained for the temperature dependence of exciton diffusion length and luminescence lifetime revealed that the dominant exciton scattering mechanism in MgZnO nanorod is exciton-phonon assisted piezoelectric field scattering.

Arrays of wires and dots have been fabricated by electron beam lithography and Ar+ ion beam etching from CdTe / ZnTe quantum wells. The intrinsic exciton photoluminescence recombination (X line) is observed for wires (dots) as small as 100 nm (130 nm). In addition, photoluminescence intensity from excitons bound to localized centres (Y line) can be detected for the smallest wires (40 nm) and for the dots down to 100 nm. The emission intensity variation together with the polarization rate are also investigated as a function of the grating period.

CdTe / CdMnTe graded index separate confinement heterostructures have been used to produce visible laser emission under electronic or photo-pumping. The optical gain of the structures has been measured as a function of optical power and temperature. The maximum gain, about 190 cm -1 for a structure containing two quantum wells, is easily attained under excitation of about 6 kW / cm 2 at 90 K. It decreases with increasing temperatures, displaying two distinct regimes: (i) in the low temperature regime (below 200–250 K), the gain decreases exponentially with a characteristic temperature T 0 = 110 K, and is interpreted as being due to the escape of holes from quantum wells and also to scattering of carriers by LO phonons; (ii) above 250 K, a faster decrease of gain takes place as a result of the thermal activation of carriers into the barriers.