Electron Microprobe and Photoluminescence Analysis of Europium-Doped Gallium Nitride Light Emitters
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L6.15.1
ELECTRON MICROPROBE AND PHOTOLUMINESCENCE ANALYSIS OF EUROPIUM-DOPED GALLIUM NITRIDE LIGHT EMITTERS R.W. Martin a, S. Dalmasso a, K.P. O’Donnell a, Y. Nakanishi b, A.Wakahara b, A. Yoshida b & the RENiBEl Network a Department of Physics, Strathclyde University, Glasgow, G4 0NG, U.K. b Toyohashi University of Technology, Tenpaku, Toyohashi, 441-8580, Japan ABSTRACT Rare-earth doped GaN structures offer potential for optical devices emitting in the visible region [1,2]. We describe a study of MOVPE grown GaN-on-sapphire epilayers implanted with Europium ions, producing characteristic red emission lines between 540 and 680 nm due to intra4f(n) electron transitions. As-implanted and subsequently annealed samples are investigated using a combination of wavelength dispersive x-ray analysis (WDX), electron microscopy, cathodoluminescence (CL) and photoluminescence (PL). WDX is shown to be a powerful technique for quantifying rare-earth concentrations in GaN, with varying electron beam voltages allowing a degree of depth profiling, further enhanced by the simultaneous collection of room temperature luminescence (CL) from the analysed region [3]. The intensities of the sharp lines observed in the luminescence spectrum are compared to the doping density (between 1014 – 1015 cm-2) and the Eu content measured by WDX, using a Eu-doped glass standard. Differences observed in the luminescence spectra produced by laser and electron beam excitation will be discussed along with the importance of the annealing conditions, which “heal” defects visible in the electron micrographs. INTRODUCTION Rare earth (RE) ions, such as Nd, Er and Eu, are found in a range of important optoelectronic applications, including solid state lasers and phosphors. They have a partially filled 4f shell shielded by completely filled outer 5s and 5p levels, resulting in very sharp optical emissions due to 4f-4f electron transitions with energies largely independent of the host material. For example, doping with europium, erbium and thulium, respectively, can generate red, green and blue emissions. The host material does play an important role in the thermal quenching of the luminescence and wide band-gap semiconductors, such as GaN, have been shown to be particularly good in this respect [1,4]. Alongside this low thermal quenching additional attractions of investigations into RE:GaN include its high radiation hardness [4] and the proven success of nitride (mainly InGaN based) based optoelectronic devices. In this paper we describe experiments on Eu doped GaN thin films and relate measurements of the Eu composition to the optical properties, measured with laser and electron beam excitations. The samples are annealed to repair damage resulting from the Eu implantation and the effects of this on the optical and structural properties are explored.
L6.15.2
SAMPLE DETAILS AND EXPERIMENTAL TECHNIQUES GaN on sapphire epilayers grown by MOVPE were implanted with 200 keV Eu ions at doses of 1014 and 1015 cm-2, as described previously [4,5]. Following implanta
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