Luminescence properties of amorphous AlN thin film phosphors incorporated with mixtures of Tb, Cu or Cu, Cr
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Luminescence properties of amorphous AlN thin film phosphors incorporated with mixtures of Tb, Cu or Cu, Cr Andrea L. Martin, Meghan L. Caldwell, Martin E. Kordesch, Chance M. Spalding, Paul G. Van Patten, and Hugh H. Richardson Condensed Matter & Surface Science Program Ohio University Athens, OH 45701 ABSTRACT Amorphous thin films of AlN doped with Cu (blue luminescence), Tb (green luminescence) and Cr (red luminescence) were deposited on p-doped Si (111) substrates using RF magnetron sputtering in a nitrogen atmosphere and made luminescent active by heat treatment at 1000oC. Single layered amorphous AlN films deposited with Tb and Cu showed cathodoluminescence from only the Tb3+ ions. Presumably, energy is transferred from Cu luminescence centers to Tb centers in close proximity. In contrast to this, double layered amorphous AlN films doped with Cu (~200 nm) on top of Tb (~50 nm) emits from both ions. This behavior is observed in a double layered amorphous AlN film doped with Cu (~200 nm) on top of a Cr (~200 nm) doped film. Secondary-ion mass spectrometry depth profiling revealed that the incorporated metals moved from one layer into the other during the heat treatment step necessary for luminescence activation. INTRODUCTION Advances are currently underway involving Group III nitride thin film semiconductors. AlN and GaN possess attractive chemical properties such as wide, direct band gaps (6.2 eV for AlN and 3.4 eV for GaN), high melting points, and large luminescence intensities as well as electrical, optical, dielectrical, and acoustical properties. While some II-VI semiconductors also have wide band gaps, they unfortunately possess weak bond strengths. Since III-nitrides have strong bond strengths and high melting points, they can be fabricated into high temperature resistors [1]. Previously, rare-earth metals such as Er3+, Eu3+, Pr3+, Tm3+, and Tb3+ have been incorporated into GaN and AlN thin films resulting in strong luminescence in the visible region [2-6]. Emission in the visible region has been observed for both amorphous and crystalline rare earth III-V materials. Studies are currently underway for the fabrication of light emitting diodes (LED’s) and electroluminescent devices (ELD’s) [7-8]. Amorphous films have an advantage over crystalline because deposition of the films does not have to occur at high temperatures, and there is low stress on the structure due to lattice mismatch. Transitions metals have been used as luminescence centers in II-VI materials, but little attention has been given to III-V materials. Advances have recently been made towards incorporating transitions metals such as Mn (red), Cr (red), and Cu (blue) into amorphous AlN [8, 9] and AlN is the semiconductor of interest because it demonstrates excellent chemical and thermal stability as well as high resistivity [10]. Contrary to lanthanide metals, transition metals can form various charged ions each with their own G6.5.1
set of energy levels. Local fields from the III-V semiconductors affect these energy levels of the transiti
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