Luminescence and lifetime properties of europium doped gallium nitride compatible with CMOS technology
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Luminescence and lifetime properties of europium doped gallium nitride compatible with CMOS technology Carl B. Poitras, Michal Lipson, Huaqiang Wu and Michael G. Spencer Department of Electrical and Computer Engineering, Cornell University, Ithaca, NY 14853 ABSTRACT Continuous-wave and time resolved photoluminescence measurements on europium doped gallium nitride in the form of a powder are presented. The powder is obtained from reacting NH3 and a melt of gallium and europium with bismuth as a wetting agent. Photoluminescence from continuous wave excitation above the GaN bandgap reveals that an optimal concentration of about 1 at.% of Eu gives the most intense emission at 621 nm. Above gap time resolved photoluminescence reveals that energy transfer between the host material (GaN) and the rare earth ions occurs at a faster rate than previously reported for MBE grown GaN:Eu. Applications of the powder are directed towards CMOS compatible light emitters that are spun on silicon. A high temperature anneal of the powder shows no change in the CW photoluminescence spectrum of the powder, confirming CMOS compatibility.
INTRODUCTION Since the first demonstration at 20K of emission from Er in III-V semiconductors and silicon [1], rare earth (RE) doped host semiconductors have spurred great interest for applications such as optical telecommunications and displays [2-4]. The use of a wider bandgap material like GaN offers the distinct advantages that it is a direct transition, which in turn results in very low thermal quenching and increases the luminescence of the rare earth ions [5]. The luminescence exhibited by the RE ions from within the GaN host material is via an energy transfer mechanism from the host material to the ions when the excitation is above the bandgap of the GaN (3.4 eV). RE doped GaN in the form of a powder, in contrast to previously studied MBE [6], MOCVD [7] and HVPE [8] grown materials in bulk form for example, offers the promise of light emitters that can be spun on silicon and are CMOS compatible. Here we study such a powder and compare its optical properties to those of RE doped GaN in bulk form.
EXPERIMENTAL DETAILS The GaN:Eu powder was fabricated as described in [9], with the exception of using Eu instead of Er. All measurements were performed at room temperature using a 0.64 m single grating monochromator equipped with a Hamamatsu R928 photomultiplier tube. Continuous wave photoluminescence (CWPL) measurements were done using a HeCd laser (325 nm) with ~0.2 W/cm2. Time resolved photoluminescence (TRPL) measurements were performed on the 621 nm emission of the GaN:Eu powder (1 at.% Eu) under optical excitation using a pulsed N2 laser (337.1 nm) with pulse width of ~4ns, and energy of about 2 µJ/cm2 at a repetition rate of 29
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Hz. The decaying signal at the output of the photomultiplier tube was measured with a LeCroy 9374L 1GHz oscilloscope.
DISCUSSION Figure 1 shows the spectra for pure GaN powder along with those for GaN:Eu powders with increasing europium concentrations of 0
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