Correlating Composition and Luminescence Variations in AlInGaN epilayers

Epilayers of the quaternary alloy AlxInyGa1 x yN have been grown on GaN/sapphire templates by plasma-assisted molecular beam epitaxy. The emission properties and elemental compositions of these samples were evaluated simultaneously and intercorrelated by combining hyperspectral cathodoluminescence imaging and wavelength-dispersive X-ray mapping. Use was made of inherent variations in growth temperature across a single epilayer to study the resultant effect on the different metal fractions and luminescence emission wavelength. By examining statistical correlations in this data, the interdependence of the fractions of constituent binary compounds, together with the associated changes in emission characteristics, can be clarified without the need to grow a systematic series of samples

Influence of the annealing ambient on structural and optical properties of rare earth implanted GaN

GaN films were implanted with Er and Eu ions and rapid thermal annealing was performed at 1000, 1100 and 1200 ⁰C in vacuum, in flowing nitrogen gas or a mixture of NH₃ and N₂. Rutherford backscattering spectrometry in the channeling mode was used to study the evolution of damage introduction and recovery in the Ga sublattice and to monitor the rare earth profiles after annealing. The surface morphology of the samples was analyzed by scanning electron microscopy and the optical properties by room temperature cathodoluminescence (CL). Samples annealed in vacuum and N₂ already show the first signs of surface dissociation at 1000 ⁰C. At higher temperature, Ga droplets form, at the surface. However, samples annealed in NH₃+N₂ exhibit a very good recovery of the lattice along with a smooth surface. These samples also show the strongest CL intensity for the rare earth related emissions in the green (for Er) and red (for Eu). After annealing at 1200 ⁰C in NH₃+N₂ the Eu implanted sample reveals the channeling qualities of an unimplanted sample and a strong increase of CL intensity is observed

CUORE and CUORE-0 experiments

Neutrino oscillation experiments proved that neutrinos have mass and this enhanced the interest in neutrinoless double-beta decay (0vßß). The observation of this very rare hypothetical decay would prove the leptonic number violation and would give us indications about neutrinos mass hierarchy and absolute mass scale. CUORE (Cryogenic Underground Observatory for Rare Events) is an array of 988 crystals of TeO2, for a total sensitive mass of 741 kg. Its goal is the observation of 0vßß of 130Te. The crystals, placed into the a dilution cryostat, are operated as bolometers at a temperature close to 10 mK. CUORE commissioning phase has been concluded recently in Gran Sasso National Laboratory, Italy, and data taking is expected to start in spring 2017. If target background rate is reached (0.01counts/day/keV/kg), the sensibility of CUORE will be, in five years of data taking, T1/21026years (1? CL). In order to test the quality of materials and optimize the construction procedures, the collaboration realized CUORE-0, that took data from spring of 2013 to summer 2015. Here, after a brief description of CUORE, I report its commissioning status and CUORE-0 results

Lowering the CUORE energy threshold

The Cryogenic Underground Observatory for Rare Events (CUORE) is a ton-scale double beta decay experiment based on TeO2 cryogenic bolometers and is currently in the last construction stage at the Gran Sasso National Laboratory (LNGS). Its primary goal is to observe neutrino-less double beta decay of 130Te, however thanks to the ultra-low background and large projected exposure it could also be suitable for other rare event searches, as the detection of solar axions, neutrinos from type II supernovae or direct detection of dark matter. The sensitivity for these searches will depend on the performance achieved at the low energy threshold. For this reason a trigger algorithm based on continuous data filtering has been developed which will allow lowering the threshold down to the few keV region. The new trigger has been tested in CUORE-0, a single-tower CUORE prototype consisting of 52 TeO2 bolometers and recently concluded, and here we present the results in terms of trigger efficiency, data selection and low-energy calibration

Status and prospects for CUORE

CUORE is a cryogenic detector consisting of 988 TeO2 crystals, 750 g each, and will be operated at a temperature of ~10 mK, to search for neutrinoless double beta decay (0¿ßß) of 130Te. The detector, in the final stages of construction at the Laboratori Nazionali del Gran Sasso (Italy), will start its operations in 2016. CUORE-0, its pilot experiment, has proven the feasibility of CUORE, demonstrating that the target background of 0.01 counts/keV/kg/y and the energy resolution of 5 keV are within reach. CUORE-0 also made the most precise measurement of the 2¿ßß decay. The expected sensitivity of CUORE to the 0¿ßß 130Te half-life is 9 •1025y, for 5 years of data taking. Here, we report the most recent results of CUORE-0, their implications for CUORE, and the current status of the CUORE experiment

First Results from CUORE: A Search for Lepton Number Violation via 0νββ0\nu\beta\beta Decay of 130^{130}Te

International audienceThe CUORE experiment, a ton-scale cryogenic bolometer array, recently began operation at the Laboratori Nazionali del Gran Sasso in Italy. The array represents a significant advancement in this technology, and in this work we apply it for the first time to a high-sensitivity search for a lepton-number-violating process: Te130 neutrinoless double-beta decay. Examining a total TeO2 exposure of 86.3 kg yr, characterized by an effective energy resolution of (7.7±0.5)  keV FWHM and a background in the region of interest of (0.014±0.002)  counts/(keV kg yr), we find no evidence for neutrinoless double-beta decay. Including systematic uncertainties, we place a lower limit on the decay half-life of T1/20ν(Te130)>1.3×1025  yr (90% C.L.); the median statistical sensitivity of this search is 7.0×1024  yr. Combining this result with those of two earlier experiments, Cuoricino and CUORE-0, we find T1/20ν(Te130)>1.5×1025  yr (90% C.L.), which is the most stringent limit to date on this decay. Interpreting this result as a limit on the effective Majorana neutrino mass, we find mββ<(110-520)  meV, where the range reflects the nuclear matrix element estimates employed