Green Emissison from Er-Doped AlN Thin Films Prepared by RF Magnetron Sputtering

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Green Emission from Er-Doped AlN Thin Films Prepared by RF Magnetron Sputtering V. I. Dimitrova, F. Perjeru, Hong Chen and M. E. Kordesch Physics & Astronomy Department, and Condensed Matter & Surface Science Program, Ohio University, Clippinger Labs, Rm. 251 Athens, OH 45701, U.S.A. ABSTRACT Thin films of Er doped AlN, ~ 200 nm thick, were grown on indium tin oxide/aluminum titanium oxide/glass substrates using RF magnetron sputtering in a pure nitrogen atmosphere. To optically activate Er all films were subject to post-deposition annealing in flowing nitrogen atmosphere at atmospheric pressure at temperatures between 1023-1223 K for 10-60 minutes. The visible cathodoluminescence (CL) in the green was detected at both 11 K and 300 K. The strongest CL peaks were observed at 558 nm and 537 nm (11 K), which correspond to the transitions from 4S3/2 and 2H11/2 to the 4I15/2 ground level. Electroluminescence (EL) studies of AlN:Er alternating-current thin-film electroluminescent (ACTFEL) devices were performed at 300 K. The turn-on voltage was found to be around 80-100 V for our ACTFEL devices. The intensity of the EL emission rapidly increases with the voltage increasing in the investigated range of 110-130 V. INTRODUCTION Recently, intense research on rare-earth (RE)-doped III-nitride semiconductor thin films has been performed because of their potentially significant new application in display technologies [1]. Considerable work has been done mainly on GaN doped with a variety of RE elements for a light-emitting diodes (LEDs) fabrication. Visible, room temperature photoluminescence (PL) and cathodoluminescence (CL) emission from various RE elements (Er, Tm, Eu, Dy, Pr and Tb) have been observed in GaN [2-6]. In addition to PL and CL, Steckl and coworkers have observed strong visible room temperature green and blue electroluminescence (EL) emission from Er and Tm-doped GaN-based Shottky LEDs and electroluminescent devices (ELD) [7,8]. These GaN films were prepared by molecular beam epitaxy (MBE) on p- Si (111) substrates, and doped by ion implantation. Visible green CL emission at low temperature and at 300 K from 3.4 at. % Er-doped amorphous AlN thin films deposited by dc reactive magnetron sputtering have also been observed [9]. The purpose of this work is to report a novel approach for obtaining strong green EL emission from amorphous AlN phosphor material doped with Er impurities. Sputtered AlN:Er films may be a promising new material as a green light emitting phosphor for use in alternatingcurrent thin-film electroluminescent (ACTFEL) device applications.

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EXPERIMENTAL DETAILS Thin films of AlN:Er were prepared by rf magnetron sputtering of an Al target of 99.999 % purity and an Er target of 99.9 % purity in pure nitrogen atmosphere. The background vacuum in the chamber was ≤ 3x10-5 Torr. All films were deposited onto 1"x1" glass substrates coated with layers of indium tin oxide (ITO) and aluminum-titanium oxide (ATO), which serve as the bottom transparent electrode and the bottom insulator, respectively.