GaN:Eu Interrupted Growth Epitaxy (IGE): Thin Film Growth and Electroluminescent Devices
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V3.1.1
GaN:Eu Interrupted Growth Epitaxy (IGE): Thin Film Growth and Electroluminescent Devices Chanaka Munasinghe1, Andrew Steckl1, a, Ei Ei Nyein2, Uwe Hömmerich2, Hongying Peng3, Henry Everitt3, Zack Fleischman4, Volkmar Dierolf4 and John Zavada5. 1
University of Cincinnati, Cincinnati, OH 45221-0030.
2
Hampton University, Hampton, VA 23668.
3
Duke University, Durham, NC 27708.
4
Lehigh University, Bethlehem, PA 18015.
5
U.S. Army Research Office, Research Triangle Park, NC 27709.
ABSTRACT The GaN:RE phosphor development plays a major role in the GaN:RE AC thick dielectric electroluminescent (TDEL) device optimization. In this paper we report on EL devices fabricated using Eu-doped GaN red phosphors films grown by interrupted growth epitaxy (IGE). IGE consists of a sequence of ON/OFF cycles of the Ga and Eu beams, while the N2 plasma is kept constant during the entire growth time. IGE growth of GaN:Eu resulted in significant enhancement in the Eu emission intensity based primarily at 620.5nm. The increase in the material crystallinity observed with the IGE phosphors appears to be the dominant cause of the emission enhancement. Thick dielectric EL devices fabricated on glass substrates using IGE-grown GaN:Eu have resulted in luminance of ~1000 cd/m2 .
INTRODUCTION During GaN:RE growth RE ions compete for the substitutional vacancies in the Ga sub-lattice. Therefore, slightly nitrogen-rich growth conditions are more suitable for RE incorporation. Nevertheless, the deviation from the stoichiometric growth condition adversely affects the crystallinity of the material. Poor crystallinity in the phosphor material hinders the hot carrier transport quality and therefore the electroluminescence (EL).
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V3.1.2
In conventional MBE, all molecular beams (Ga and N) are incident upon the growth surface simultaneously throughout the entire period and the constituent atoms and molecules are deposited on the substrate preferably under stable group V conditions resulting a continuous growth. The short nitrogen radical lifetime on the surface allows only for very rapid reaction of Ga and N and immediate formation of GaN crystals [1]. Therefore, the MBE growth technique frequently results in the formation of a large number of GaN islands on the substrate surface due to the severe limitations in Ga atom migration on the surface at the relatively low MBE growth temperatures [2, 3]. The island formation tends to induce a columnar growth of the material and results in poor morphology and electrical properties. Several techniques have been investigated in order to enhance the quality of the semiconductor material, including shutter control method [4], nitrogen beam modulation [5], and migration enhanced epitaxy (MEE) [6]. All these techniques have as a common feature the goal of increasing the surface migration of Ga atoms during GaN growth. A schematic illustrating the source shutter sequences in MBE and MEE processes is shown in Fig. 1. The nitrogen flux is interrupted periodically at a constant
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