Photoluminescence and Cathodoluminescence of GaN doped with Pr
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Electronic address: [email protected] Permanent address: Institute of Physics, Laboratory of Solid State Optoelectronics, Nicholas Copernicus University, Grudziadzka 5, 87-400 Torun, Poland 2
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postimplant isochronal thermal annealing treatments (duration 0.5 h and 1 h) at temperature 11000C in NH3, N2, Ar2, and in forming gas (N2+H2). The emission spectra presented are obtained from samples annealed at 11000 C, which seems to be the optimal annealing temperature for RE ions incorporated as the luminescent center. The photoluminescence spectra and kinetics measurements were performed using a He-Cd (325 nm) and N2 (337 nm) lasers. The PL kinetics were measured using a double grating monochromator DIGIKROM CM112 assembled with Hamamatsu R928 (or R616) photomultipliers and a photon counting system with a turbo-multichannel scaler (Turbo-MCS, EG&G). The CL was excited by an electron beam incident upon the sample at a 450 angel from an electron gun (Electron gun system EK-2035-R (500V and 20 kV) which was in a common vacuum ( of ~5×10-7 torr) with the cryostat. ENERGY LEVELS, AND EXCITATION PROCESSES The very important question is where the trivalent rare earth ions are incorporated in GaN: at substitutional sites on the metal sublattice and/or interstitial sites. In a hexagonal GaN crystal the Ga atoms occupy sites of symmetry C3v (similar to Zn atoms in ZnS wurtzite phase) and two distinct high-symmetry interstitial positions also with C3v symmetry[4a,b]. Recently, using the emission channeling (EC) technique, the lattice site occupations of RE elements in GaN were determined as a relaxed substitutional Ga-sites with an average relaxation of about 0.025 nm [5]. The rare earth ions can also aggregate especially at high concentration, as well as create complex centers in the presence of an anther ion e.g. oxygen . In this paper we studied the PL and CL and kinetics of GaN implanted with Pr. The Pr3+ free ion possesses 4f 2 configuration which gives rise to a 3H4 ground state and 3H5,6, 3F2,3,4, 1G4, 1D2, 3P0,1, 1I6, 3P2, and 1S0 excited states. If the crystal field symmetry at the Pr3+ site is known, then the number and symmetry of crystal field levels and the selection rules for transitions between these levels can be calculated. In C3v crystal symmetry the states with J = 0, 1, 2, 3, 4, 5, 6, will split into 1(0), 1(1), 1(2), 3(2), 3(3), 3(4), 5(4), single(doubly) degenerate crystal field LSJ levels, respectively. The rare earth ions located at a specific crystal site are associated with characteristic optical transitions subject to the selection rules that are governed by the crystal symmetry of the site. It is generally accepted that rare earth impurities in III-V semiconductors create isoelectronic traps [6]. The outer electron configurations of RE3+ ions ar
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