InGaN based LEDs are known to be very efficient in the blue range. However, although InGaN can theoretically cover all visible range, quantum efficiency drops when emission wavelength emission is increased due to quantum confined Stark effect. Furthermore, indium incorporation is hindered by compressive strain induced by lattice mismatch between InGaN and GaN. To tackle the lattice mismatch problem, a full InGaN structure on a relaxed InGaN substrate is proposed.
The structure consisting of five InxGa1-xN / InyGa1-yN multi quantum wells on top of an InyGa1-yN buffer layer is grown by MOVPE on an InGaNOs substrate from Soitec company. Three InGaNOs substrates of lattice parameters of 3.190, 3.200 and 3.205 Ångströms were co-loaded in order to compare their ability to incorporate indium for the same growth conditions. For reference, a sample grown on GaN template will allow us to compare the wavelength red-shift resulting of the use of InGaNOs template.
The samples were characterized by photoluminescence at room temperature using 375 nm and 405 nm laser diodes. It is shown that long wavelengths can be reached thanks to the use of InGaNOs substrates. For same active region growth conditions as reference sample, a red-shift up to 65 nm (from 445 to 510 nm) is observed, demonstrating InGaNOs potential for easier In incorporation. Using different growth conditions, wavelengths up to 600 nm have been reached. First internal quantum efficiency measurements demonstrate a good quality material. InGaNOs seems promising for emission in the “green gap”and beyond.
I. Robin, P. Ferret, A. Dussaigne, C. Bougerol, D. Salomon, X. Chen, M. Charles, P. Tchoulfian, A. Gasse, A. Lagrange, M. Consonni, H. Bono, F. Levy, Y. Desieres, A. Aitmani, S. Makram-Matta, E. Bialic, P. Gorrochategui, L. Mendizabal
With a long experience in optoelectronics, CEA-LETI has focused on Light Emitting Diode (LED) lighting since 2006. Today, all the technical challenges in the implementation of GaN LED based solid state lighting (SSL) are addressed at CEA-LETI who is now an RandD player throughout the entire value chain of LED lighting. The SSL Line at CEA-LETI first deals with the simulation of the active structures and LED devices. Then the growth is addressed in particular 2D growth on 200 mm silicon substrates. Then, technological steps are developed for the fabrication of LED dies with innovative architectures. For instance, Versatile LED Array Devices are currently being developed with a dedicated μLED technology. The objective in this case is to achieve monolithical LED arrays reported and interconnected through a silicon submount. In addition to the required bonding and 3D integration technologies, new solutions for LED chip packaging, thermal management of LED lamps and luminaires are also addressed. LETI is also active in Smart Lighting concepts which offer the possibility of new application fields for SSL technologies. An example is the recent development at CEA LETI of Visible Light Communication Technology also called LiFi. With this technology, we demonstrated a transmission rate up to 10 Mb/s and real time HD-Video transmission.
We report on the epitaxy of vertically aligned ZnO nanowires (NWs), the collective integration technology of these
nanowires and their optical and electrical characterizations. ZnO based nanowires are grown mainly on sapphire
substrates by metal-organic vapour phase epitaxy (MOVPE). Photoluminescence spectra at 4 K exhibit strong excitonic
peaks at around 380 nm without green luminescence band, showing the low deep radiative defect density. Technological
processes have been developed both for mineral and organic integrations of the as-grown nanowires. Photoconducting
properties in the UV-visible range have been investigated through collective electrical contacts. The electrical transport
properties of vertically integrated single nanowires have also been investigated by current sensing AFM measurements.
A comparison of the PL spectra at 300 K of the as-grown and integrated nanowires has shown no significant impact of
the integration process on the crystal quality of the nanowires.
F. Levy, Y. Desieres, P. Ferret, S. Fichet, S. Gidon, P. Gilet, P. Noel, I.-C. Robin, E. Romain-Latu, M. Rosina, R. Songmuang, G. Feuillet, B. Daudin, A. Chelnokov
LEDs based on semiconductor nanowires are a promising alternative to the standard planar devices to achieve low cost high yield manufacturing for the general lighting applications. The expected advantages of such structures are a high crystalline quality of the heterostructures, compliance with a large range of substrates and light extraction enhancement. We report here on the present status of our research work concerning the electromagnetic simulation of nanowire emission, the epitaxy of near-UV semiconductor vertically aligned nanowires, the collective integration technology of these nanowires and their characterizations.
A sensor based on selective optical absorption allows monitoring of hazardous engine exhaust emissions such as gaseous hydrocarbons and carbon monoxide. The IR components presented here offer the potential to develop a compact, fast and selective sensor reaching the technical and cost requirements for on-board automotive applications. Optical gas monitoring requires light sources above 3 μm since most of the gas species have their fundamental absorption peaks between 3 and 6 μm. We report here on resonant microcavity light sources emitting at room temperature between 3 and 5 μm. The emitter combines a CdxHg1-xTe light emitting heterostructure and two dielectric multilayered mirrors. It is optically pumped by a commercial III-V laser diode. The principle of the resonant microcavity emitter allows tailoring of the emission wavelength and the line width to fit the absorption band of a specific gas, ensuring a very good selectivity between species. Moreover, this kind of emitter allows fast modulation enabling high detectivity and short response time. We report performances of light sources in the range 3 - 5 μm allowing the detection of hydrocarbons and carbon monoxide. Association of emitters peaking at different characteristic wavelengths with a single broad band detector allows designing of an optical sensor for several gas species. Sensitivity and time response issues have been characterized: detection of less than 50 ppm of CH4 on a 15 cm path has been demonstrated on synthetic gas; analysis of exhaust gases from a vehicle has allowed the resolution of a cylinder time. This optical sensor offers the potential of various on-board automotive applications.
A sensor based on selective optical absorption allows monitoring of hazardous engine exhaust emissions such as gaseous hydrocarbons and carbon monoxide. The IR components presented here offer the potential to develop a compact, fast and selective sensor reaching the technical and cost requirements for on-board automotive applications. Optical gas monitoring requires light sources above 3μm since most of the gas species have their fundamental absorption peaks between 3 and 6 μm. We report here on resonant microcavity light sources emitting at room temperature between 3 and 5μm. The emitter combines a CdxHg1-xTe light emitting heterostructure and two dielectric multilayered mirrors. It is optically pumped by a commercial III-V laser diode. The principle of the resonant microcavity emitter allows tailoring of the emission wavelength and the line width to fit the absorption band of a specific gas, ensuring a very good selectivity between species. Moreover, this kind of emitter allows fast modulation enabling high detectivity and short response time. We report performances of light sources in the range 3-5μm allowing the detection of hydrocarbons and carbon monoxide. Association of emitters peaking at different characteristic wavelengths with a single broad band detector allows designing of an optical sensor for several gas species. Sensitivity and time response issues have been characterized: detection of less than 50ppm of CH4 on a 15cm path has been demonstrated on synthetic gas; analysis of exhaust gases from a vehicle has allowed cylinder to cylinder resolution. This optical sensor offers the potential of various on-board automotive applications.
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