Effect of Crystalization on Photoluminescence of ER 2 O 3 Thin Films
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EFFECT OF CRYSTALIZATION ON PHOTOLUMINESCENCE OF ER2O3 THIN FILMS XIAOMAN DUAN, SAJAN SAINI, KEVEN CHEN, MICHEL LIPSON, JURGEN MICHEL AND LIONEL C. KIMERLING MIT, Department of Materials Science and Engineering, Cambridge, MA 02139 USA
ABSTRACT The effect of microstructures on the photoluminescence of Er2O3 thin films has been systematically studied in this paper. The Er2O3 film was fabricated via reactive sputtering of Er metal in an Ar/O2 atmosphere. The as-deposited thin film contained both amorphous and polycrystalline structures, which showed weak photoluminescence at 1.55 µm. Annealing at an elevated temperature from 650 to 1050 °C in O2 ambient significantly incorporated oxygen into the lattice and strongly promoted crystalline grain growth, which in turn dramatically induced the transaction of photoluminescence from 1.55 µm to 1.541 µm. The ideal large crystal Er2O3 structure with fcc-Er2O3 and bcc-Er2O3 precipitates was obtained by conducting a two-step annealing (650 °C for 5 hours followed by 1020 °C for 2 hours) which resulted in a sharp photoluminescence peak at 1.541 µm. Further significant enhancement of PL at 1.541 µm was achieved via RTA at 1050 °C for 30 seconds to introduce more fcc-Er2O3 precipitates into the bcc-Er2O3 matrix. 1. INTRODUCTION Er2O3 is a potential luminescent material for future Si microphotonic devices [1]. Due to the fact that the equilibrium concentration of Er3+ ions in Er2O3 can be significantly higher than that in solid solubility limited Er-doped systems, Er2O3 could yield much higher luminescence intensity at 1.541 µm over the Er-doped systems [2-4]. Although processing of thin Er2O3 films via sputtering has been reported [5-11] and room temperature photoluminescence has been achieved, the grain structure and the luminescent behavior of the different phases as well as the defects are not yet well understood. A better understanding of the nucleation, growth and microstructures will facilitate better control over the structures and, in turn, better optical properties in the Er2O3 films. The aim of this study is therefore to identify and optimize the material structures that are most favorable to photoluminescence at 1.541 µm. 2. EXPERIMENTAL In this study, the Er2O3 films were grown on SiO2 above a silicon substrate by reactive magnetron sputtering of Er metal in a Kurt J. Lesker system. Ultra-high vacuum conditions,
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