Visible Luminescent Activation of Amorphous AlN:Eu Thin-Film Phosphors with Oxygen
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Internet Journal Nitride Semiconductor Research
Visible Luminescent Activation of Amorphous AlN:Eu Thin-Film Phosphors with Oxygen Meghan L. Caldwell2, P. G. Van Patten2, Martin E. Kordesch1 and Hugh H Richardson2 1Condensed
Matter and Surface Science Program, Department of Physics and Astronomy, Ohio University, of Chemistry and Biochemistry, Ohio University,
2Department
(Received Friday, June 15, 2001; accepted Tuesday, August 28, 2001)
We have investigated the effects of oxygen incorporation on cathodoluminescence (CL) and photoluminescence (PL) from sputtered amorphous films of AlN:Eu3+. Ordinarily, these materials must be activated at elevated temperatures (~1000K) before appreciable luminescence can be observed. We have shown that oxygen doping is an effective alternative to thermal activation. Studies of CL intensity versus oxygen contamination indicate that luminescence turns on if the oxygen content of the sputtering plasma exceeds a few percent. Significantly, oxygen appears to have a greater impact (>600-fold) on luminescence than does thermal activation (100-fold). The oxygen dependence of PL intensity varies slightly from that of CL intensity. A possible explanation for this observation is proposed. The results suggest that low temperature alternatives to the customary thermal activation process may be available. Such alternatives would eliminate materials constraints and would permit the facile integration of plastic components or substrates with rare-earth-doped IIIN luminescent devices.
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Introduction
The III-nitrides (III-N) are interesting semiconductors because of their superior electrical, optical, thermal, and acoustical properties, as well as chemical and physical stability. Phosphors based on III-N host materials were first realized when visible emission was observed from Er-doped GaN [1]. Since this initial breakthrough, a number of rare-earth-doped III-N phosphors have been prepared [2] [3] [4] [5] [6] [7] [8] [9] [10]; these phosphors cover the entire visible spectrum. Most of these phosphors have employed single-crystal host matrices, and these crystalline phosphors have performed admirably. Unfortunately, high quality, defect-free films are apparently required to realize the full performance potential of the crystalline films. Additionally, most of these materials require growth and/or post-processing at elevated temperatures. The requirements for high quality crystalline materials and for high temperature luminescence activation represent undesirable constraints that severely limit scale-up potential, cost efficiency, and device design options. A recent theoretical paper asserted that an amorphous III-N semiconductor could serve as a useful electronic material [11]. This revelation prompted activity
in growing amorphous III-N materials and many doped amorphous III-N phosphors have subsequently been reported that emit in the visible range [12] [13] [14] [15] [16] [17]. The development of amorphous materials suitable for device fabrication ameliorates some of the materials constr
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