Journal of Luminescence 126 (2007) 695–701 Theoretical investigation of a single erbium center in hexagonal gallium nitride Ramzi Maaˆlej à , M. Dammak, S. Kammoun, M. Kammoun Laboratoire de Physique Applique´e, Groupe de Physique The´orique, De´partement de Physique, Faculte´des Sciences de Sfax, 3018 Sfax, Tunisie Received 30 June 2006; received in revised form 21 October 2006; accepted 31 October 2006 Available online 23 January 2007 Abstract A theoretical energy-level analysis was based on parametric Hamiltonian for the 4f 11 electronic configuration of Er 3+ ions in C 3v center, and it permitted a phenomenological characterization of crystal-field (CF) Hamiltonian parameters. This characterization allowed us to calculate the energy of the missing stark levels of the 4 I 15/2 and 4 I 13/2 states and to confirm the presence of a single emission center with C 3v symmetry. The calculated CF and strength parameters are compared with those obtained for Sm 3+ , Pr 3+ and Yb 3+ ions in the same host and with Er 3+ in other isostructural hosts. r 2006 Elsevier B.V. All rights reserved. PACS: 71.70.Ch Keywords: GaN; Erbium; Photoluminescence; Crystal-field 1. Introduction In recent years, many studies have been devoted to the physical properties of rare earth (RE)-doped III–V compound semiconductors. Gallium nitride (GaN) is by far the most extensively studied semiconductor of III–V nitrides due to the very important technological applica- tions of this semiconductor as laser diodes [1–4]. Conventional III–V nitride semiconductors doped with RE ions exhibit limited photoemission at room tempera- ture due to low RE solubility and severe quenching of the luminescence at room temperature. Since it was shown that the thermal quenching in Er-doped semiconductors de- creases with increasing band gap [5], GaN become a very attractive host material for RE device applications as electroluminescent light emitters operating at wavelengths from visible to the infrared (IR) spectral range [6,7]. Although the variety of applications, GaN-doped rare earths spectra still not well resolved and understood. Then appears the importance and the necessity of a theoretical investigation of the crystal-field (CF) splitting of 4f n energy levels. This investigation allows the determination of the free-ion and CF parameters of lanthanide configurations whose values are poorly known due to the lack of sufficient experimental energy (stark) level data. Due to the screening effect by the outer 5s 2 and 5p 6 electrons, the transitions between the incompletely filled 4f shell electrons emit sharp and temperature-stable lumines- cence that is slightly sensitive to the surrounding host environment. Among the various combinations of the RE ions and III–V hosts, we are particularly interested in GaN:Er. Indeed, due to the importance of 1.54 mm region for telecommunications, erbium has received considerable attention [8,9]. Emission of Er 3+ ions in GaN was intensively studied by different groups of authors [10–17]. However, due to the complexity of the photoluminescence (PL) spectra around 1.54 mm, Er 3+ optical properties in GaN are still not well understood. The number of centers that can be observed in luminescence depends on erbium concentration, grown and annealing conditions, excitation conditions, etc. For example, up to nine different erbium centers in GaN were found for near band-gap excitation [18]. In order to reduce the number of centers, high-purity hexagonal GaN layers were implanted by low erbium ARTICLE IN PRESS www.elsevier.com/locate/jlumin 0022-2313/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jlumin.2006.10.029 à Corresponding author. Tel.: +216 74 45 26 32; fax: +216 74 24 28 70. E-mail address: ramzi.maalej@fss.rnu.tn (R. Maaˆlej).