Characterization of the blue emission of Tm/Er co-implanted GaN
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Characterization of the blue emission of Tm/Er co-implanted GaN I.S. Roqan1, C. Trager-Cowan1, B. Hourahine1, K. Lorenz2, E. Nogales1, K.P. O’Donnell1, R.W. Martin1, E. Alves2, S. Ruffenach3, O. Briot3. 1 Dept. of Physics, University of Strathclyde, Glasgow G4 0NG, UK. 2 ITN, Estrada Nacional 10, 2686-953 Sacavém, Portugal. 3 Groupe d’Etude des Semiconducteurs, Université Montpellier II, 34095 Montpellier, France.
ABSTRACT Comparative studies have been carried out on the cathodoluminescence (CL) and photoluminescence (PL) properties of GaN implanted with Tm and GaN co-implanted with Tm and a low concentration of Er. Room temperature CL spectra were acquired in an electron probe microanalyser to investigate the rare earth emission. The room temperature CL intensity exhibits a strong dependence on the annealing temperature of the implanted samples. The results of CL temperature dependence are reported for blue emission (~ 477 nm) which is due to intra 4f -shell electron transitions (1G4→3H6) associated with Tm3+ ions. The 477 nm blue CL emission is enhanced strongly as the annealing temperature increases up to 1200oC. Blue PL emission has also been observed from the sample annealed at 1200oC. To our knowledge, this is the first observation of blue PL emission from Tm implanted GaN samples. Intra-4f transitions from the 1 D2 level (~ 465 nm emission lines) of Tm3+ ions in GaN have been observed in GaN:Tm films at temperatures between 20–200 K. We will discuss the temperature dependent Tm3+ emission in both GaN:Tm,Er and GaN:Tm samples.
INTRODUCTION Extensive studies of GaN doped with rare earths (REs) (in-situ doped during growth or implanted), have produced red, green and blue (RGB) emission from GaN:Eu, GaN:Er and GaN:Tm, respectively. The aim of these studies is to produce multiple color capability based on GaN:RE, for example, fabrication of white light LEDs through the light emission from co-doped GaN:Eu,Er,Tm. For example, Steckl et al (2001), have reported on multiple color capability based on RE-doped GaN electroluminescence [1]. Intermediate colors from GaN:RE have been reported through MBE co-doping during growth, such as turquoise from GaN:Er,Tm and orange from GaN:Eu,Er [2]. The biggest challenge in the field of light emitting RE doped GaN is to obtain blue emission from GaN:Tm with high device efficiency. In this study, we present the RE luminescence properties of GaN co-implanted with Tm and a low concentration of Er. REs in GaN replace gallium on a substitutional site of symmetry C3ν [3]. The 4f orbitals of RE ions incorporated into semiconductors are so strongly screened that energy levels of the 4f configuration are only slightly perturbed compared to free-ion energy levels [3]. Therefore, the effect of the surrounding host is weak, yielding sharp luminescence lines. We are particularly interested in the persistence of such luminescence at elevated temperature, as required for device operation. Hence we will present here CL temperature-quenching studies. We have carried out preliminar
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