Site Multiplicity of Rare Earth Ions in III-Nitrides
- PDF / 3,311,274 Bytes
- 10 Pages / 595.26 x 841.89 pts (A4) Page_size
- 99 Downloads / 170 Views
E9.6.1
SITE MULTIPLICITY OF RARE EARTH IONS IN III-NITRIDES K.P.O’Donnella, V. Katchkanova,b, K. Wanga, R.W. Martina, P.R. Edwardsa, B. Hourahinea, E. Nogalesa, J.F.W. Mosselmansb, B. De Vriesc, and the RENiBEl Consortium. a Department of Physics, Strathclyde University, Glasgow, G4 0NG, Scotland, U.K. b CLRC Daresbury Laboratories, Warrington, WA 4AD, England, UK c IKS, Katholieke Universiteit Leuven, 3001 Leuven, Belgium.
ABSTRACT This presentation reviews recent lattice location studies of rare earth (RE) ions in GaN by electron emission channelling (EC) and X-ray absorption fine structure (XAFS) techniques. These studies agree that RE ions at low concentrations (whether they are incorporated during growth or introduced later by ion implantation) predominantly occupy Ga substitutional sites, as expected from considerations of charge equivalence. We combine this result with some examples of the well-documented richness of optical spectra of GaN:RE3+ to suggest that the luminescence of these materials may be ascribed to a family of rather similar sites, all of which feature the REGa defect. INTRODUCTION RE ions in suitable hosts offer an all-nitride route to the realisation of optoelectronic devices in visible light [1]. For example, GaN doped with Tm, Er and Eu emits spectrally pure light in the blue, green and red spectral regions, respectively, which may be additively combined to stimulate most of the possible human colour responses. In contrast, it is well known that the efficiency of the commercially successful Inx Ga1-x N light emission decreases drastically with increasing wavelength [2]. This fact is well illustrated by a comparison of the composition map and the spectral imaging cathodoluminescence (CL) intensity map of the graded-composition sample, InGaN336X, which are shown in Figure 1. A shift in peak wavelength from 570 nm to 700 nm (which corresponds to an increase of InN fraction from x ~ 0.25 to 0.4) is accompanied by a decrease of more than one order of magnitude in the photoluminescence (PL) output. As far as we are aware, no comparable study has been carried out for samples, now more widely available, with InN fractions higher than x = 0.4, although at very low x, the PL and EL (electroluminescence) intensities increase with x [3]. The study of RE luminescence in semiconductors has quite a long history, in particular concerning the 1.54 µm band emitted by erbium in several hosts [4]. Favennec et al showed that wider gap semiconductors should suffer less from the temperature quenching of luminescence that is generally found in bulk hosts [5]. Application of Favennec’s principle to nitrides came with the emergence of suitable epitaxial host material in the 90’s. A recent review of the application of RE-doped nitrides to light emitting devices has been provided by Steckl et al [6]. Finally, the recently accomplished incorporation of RE ions in nitride heterostructures offers considerable promise for the future [7].
E9.6.2
10 mm
(a)
(b) 25
40%
100
1 a.u.
Figure 1 (a) Composition map of In
Data Loading...
