Lattice Location and Cathodoluminescence Studies of Ytterbium/Thulium Implanted 2H-Aluminium Nitride
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Lattice Location and Cathodoluminescence Studies of Ytterbium/Thulium Implanted 2H-Aluminium Nitride U. Vetter1, M. F. Reid2, H. Hofsäss1, C. Ronning1, J. Zenneck1, M. Dietrich3, ISOLDE Collaboration3 1 2. Physikalisches Institut, Universität Göttingen, Bunsenstr. 7-9, D-37073 Göttingen, Germany 2 Department of Physics and Astronomy, University of Canterbury, Christchurch, New Zealand 3 CERN, 1211 Geneva 23, Switzerland ABSTRACT Lattice location studies of radioactive 169Yb ions, implanted at an energy of 60 keV into 2HAlN at the on-line isotope separator ISOLDE at CERN, were performed using the emission channeling technique. The measurements, which yield a substitutional Al lattice site for the implanted ions, were recorded for annealing temperatures ranging from 293 K to 1273 K. After complete decay of 169Yb to 169Tm cathodoluminescence measurements were performed in the range 12 K – 300 K. The samples show a strong visible luminescence at 460 - 470 nm at room temperature, which is attributed to the 1D2-3F4 intra-4f electron transition of Tm3+. At 12 K the luminescence is dominated by transitions starting from the 1H6 multiplet. Time resolved as well as temperature dependent cathodoluminescence measurements are presented and discussed. The lattice location as well as the time resolved cathodoluminescence measurements suggest that there is only one pronounced site of the implanted ions in the AlN lattice and that this is the substitutional aluminium site. INTRODUCTION 2H-aluminium nitride (AlN), with its large band gap of 6.2 eV is, among the wide band gap semiconductors, a very promising candidate for the study of intra-4f electron transitions of triply ionised lanthanides and for the implementation of efficient light emitters in the near infrared, visible and ultraviolet spectrum [1-4]. However, fundamental investigations of luminescence spectra of lanthanide implanted wide band gap semiconductors are difficult because comparative absorption or reflection or selective excitation spectroscopy is not applicable due to the limited implantation fluence. A common problem is therefore the unknown site of the implanted ions. To overcome these problems direct lattice location studies are very useful. In recent years the electron emission channeling method [5] using radioactive isotopes has been very successfully applied to the determination of lattice sites of lanthanides implanted into semiconductors. EXPERIMENTAL DETAILS We implanted radioactive 169Lu ions into AlN (grown by metal-organic vapor phase epitaxy on 6H-SiC, as described in Ref. [6]) at an energy of 60 keV and fluences of 1*1013 ions/cm2 at the online isotope separator ISOLDE [7] at CERN. The ions are produced by irradiation of a tantalum target with protons accelerated to 1.6 GeV and are extracted via surface ionisation and mass separation, followed by implantation at 60 keV. After complete decay of 169Lu (T1/2 = 35 h) to 169Yb (T1/2 = 32.0 d), electron emission channeling spectra were recorded using the conversion electrons arising in the decay 16
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