Luminescence from Erbium-Doped Gallium Nitride Thin Films
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my European Research Office, London, UK NW1 5TH; *Hampton University, Department of Physics, Research Center for Optical Physics, Hampton, VA 23668; **University of Florida, Department of Materials Science and Engineering, Gainesville, FL 32611; ***U.S. Army Research Laboratory, Adelphi, MD, 20783; Kansas State University, Department of Physics, Manhattan, KN; †Consultant, Stevens Ranch, CA 91381 E-mail: [email protected] ABSTRACT The III-V nitride semiconductors appear to be excellent host materials for optical device applications involving thin films doped with rare earth atoms. In particular, GaN epilayers doped with Er ions have shown a highly reduced thermal quenching of the Er luminescence intensity from cryogenic to elevated temperatures. The remarkable thermal stability of the light emission may be due to the large energy bandgap of the material, as well as to the optical inactivity of material defects in the GaN film. In this paper we present recent developments concerning the luminescence characteristics of Er-doped GaN thins films. We have used two methods for doping GaN films with Er ions, ion implantation and in-situ incorporation during gas source metalorganic molecular beam epitaxy (MOMBE). Bandedge (at ~ 0.34 µm) and infrared (at ~ 1.54 µm) photoluminescence (PL) spectra have been measured for both types of Er-doped GaN films. Considerably different emission spectra have been observed depending upon the incorporation method and the heat treatment procedure. In situ Er-doped GaN layers have been processed into hybrid light emitting devices and emission spectra at 1.54 µm have been measured. Erbium in Semiconductors and Thermal Quenching The optical properties of rare earth ions in insulating materials have been extensively studied for applications in solid state lasers and optical fiber amplifiers [1]. Solid state lasers, such as Nd3+:YAG, are based on the 4f intra-subshell transitions of the rare earth trivalent ions (RE3+) which exhibit a very stable lasing wavelength and minimum temperature dependence. Because of these characteristics, such lasers have found widespread applications in laboratory and military systems. Er-doped silica fibers are being used for amplification of optical signals in wavelength division multiplexing (WDM) communication systems operating at 1.54 µm and Pr-doped fibers are being developed for use at 1.3 µm [2]. Investigations of the optical properties of rare earth-doped III-V semiconductors have begun relatively recently. Beginning with the work of Ennen et al. in 1983 [3], the luminescence of rare earth ions in III-V compound semiconductors has received considerable attention. The main goal of this work has been to develop electrically pumped optical sources and amplifiers for use in optical communication systems. Studies of rare earth ions in a variety of different semiconductors have been conducted [4,5,6]. Due to the importance of the 1.54 µm region for optical communications, Er has been the main rare earth element to be investigated.
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