Structure and electrical activity of rare-earth dopants in selected III-Vs
- PDF / 62,200 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 0 Downloads / 193 Views
Y5.3.1
Structure and electrical activity of rare-earth dopants in selected III-Vs J.-S. Filhol, S. Petit, R. Jones School of Physics, University of Exeter, Stocker Road, Exeter, EX4 4QL, United Kingdom B. Hourahine, Th. Frauenheim, H. Overhof Theoretische Physik, Universit¨at Paderborn, Warburger Str. 100, 33098 Paderborn, Germany J. Coutinho Department of Physics, University of Aveiro, 3810 Aveiro, Portugal M. J. Shaw, P. R. Briddon School of Natural Sciences, University of Newcastle upon Tyne, Newcastle upon Tyne, NE1 7RU, United Kingdom ¨ S. Oberg Lule˚ a University of Technology SE-97187 Lule˚ a, Sweden ABSTRACT Density functional theory is used to investigate Eu, Er and Tm rare earth (RE) impurities in GaAs, GaN and AlN. The most stable site is when the RE is located at a group III substitutional site but in GaN and GaAs these defects do not then possess any gap levels, unlike AlN. RE-VN defects in GaN are shown to possess levels which could act as traps for excitons. The interaction of oxygen with substitutional REs is also considered. INTRODUCTION In wide band gap semiconductors, rare earth (RE) dopants have recently come under increased scrutiny as they lead to sharp intra-f optical transitions which extend from the infra-red to the ultraviolet. In contrast with RE doped Si, the photoluminescence in GaN remains intense at room temperature. Indeed doping with Eu, Er and Tm leads to both room-temperature photoluminescence and electro-luminescence [1] and several emissions including respectively red, green and infra-red, and blue light emission, that could be of use as primary colors in screen displays[2]. Most of our knowledge of Er defects in GaAs comes from photoluminescence (PL) and photoluminescence excitation (PLE) data, especially when oxygen is a co-dopant as then the PL spectra are simpler and more intense (see Ref. [3] and references therein). So far, at least 11 distinct Er-related centers have been detected in PLE (labeled from center 1 to center 11), but only centers 9 and 10 are active for above band gap excitation and center 9 is the most efficient [3]. From monitoring the temperature quenching dependence of the PL under pressure [4] it is known that center 9 is activated with about 375 meV. The constancy of this energy with pressure suggests that this energy was related to E 0 or the difference between the energy of the trapped exciton and the optical emission (0.8 eV) – the ’back transfer energy’. This in turn suggests a trap level at Eg − (E0 + 0.8) eV, i.e., around Ec − 0.4 or Ev + 0.4 eV. Compared to GaAs and GaN, less is known about the lattice location and complexes of REs in AlN. At least two types of luminescent centers are known for Er doped AlN [5], excited either through direct optical pumping into 4f levels or through an indirect
Y5.3.2
carrier-mediated process. Both structural defects and oxygen are known to increase the cathodoluminescent activity of Eu and Tb [6, 7], suggesting complexes involving either native defects or O may play a role in strong luminescence. Rare-earth (R
Data Loading...
