Characterization of the Mechanism of Activation for Visible Luminescence in Tb-Doped Crystalline and Amorphous AlN Thin
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Characterization of the Mechanism of Activation for Visible Luminescence in Tb-Doped Crystalline and Amorphous AlN Thin Films C. M. Spalding,1 M. L. Caldwell,1 A. L. Martin,1 V. I. Dimitrova,2 M. E. Kordesch,2 H. H. Richardson,1 and P. G. Van Patten1 Condensed Matter and Surface Science Program, Ohio University, Athens, OH 45701-2979, U.S.A. and 1 Department of Chemistry and Biochemistry, Ohio University, Athens, OH 45701-2979, U.S.A. 2 Department of Physics and Astronomy, Ohio University, Athens, OH 45701-2979, U.S.A. ABSTRACT High-temperature treatments are necessary for luminescence ‘activation’ of sputterdeposited, RE-doped, III-nitride phosphor materials. We report an investigation of the activation process in crystalline and amorphous Tb-doped AlN films. These films were characterized before and after thermal activation at temperatures up to 1000º C by cathodoluminescence (CL), static and time-resolved photoluminescence (PL), and secondary ion mass spectrometry (SIMS). The results suggest that the absence of luminescence in unactivated and in old activated samples is due to rapid quenching of the RE excited state. Furthermore, the quenching in the activated, aged samples appears to be due to sorption of ambient water vapor. Energy transfer to a harmonic of the O-H vibration is a likely quenching pathway in these samples. Unfortunately, this water-related quenching mechanism is implausible as a candidate in freshly-made, unactivated samples since water is excluded from the growth chamber. INTRODUCTION Rare-earth (RE) doped semiconductors have generated considerable interest as materials for light-emitting devices. Recent interest has centered on III-nitrides because of their superior electro-optical, thermal, and chemical properties.[1][2][3] Most of the work in this area has concentrated on crystalline or polycrystalline GaN,[2][3] but visible emission recently has been reported from amorphous III-nitride materials doped with Er3+ and Tb3+.[4][5][6][7][8] Amorphous, sputter-deposited AlN:RE films have even been demonstrated as promising electroluminescent devices.[6][7][8] Interest in sputter deposition of these materials stems from the inherent scalability of sputtering and from the ease with which it can be integrated into a production process. Unfortunately, luminescence is not observed from freshly-sputtered, RE-doped, III-nitride materials (either crystalline or amorphous), so a high temperature (1000º C) activation step is required to induce visible luminescence. Thermal activation requirements have similarly been documented for ion-implanted III-nitrides prepared via MOCVD.[9][10] Although the activation mechanism remains unknown, this mechanism is of fundamental interest as a possible key to the production of better luminescent devices. In addition, an understanding of this mechanism may lead to alternative activation methods with less stringent requirements for thermal stability of the
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substrate. This contribution reports progress from a continuing spectroscopic study of the thermal activat
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