Lattice Location and Luminescence Behavior of Rare Earth Elements Implanted in GaN

  • PDF / 1,124,053 Bytes
  • 6 Pages / 414.72 x 648 pts Page_size
  • 78 Downloads / 213 Views

DOWNLOAD

REPORT


EXPERIMENTAL 1-2 gm thick GaN films were grown on on-axis n-type, Si-face a(6H)-SiC(000l) substrates at 1273 K and 45 Torr using a vertical, cold-wall, RF inductively heated MOVPE 1021 Mat. Res. Soc. Symp. Proc. Vol. 482 0 1998 Materials Research Society

deposition system [14]. A 0.1 jtm high-temperature (1373 K) AIN-buffer layer was deposited prior to the GaN growth. Deposition was performed using triethylaluminum (TEA) and triethylgallium (TEG) in combination with 1.5 SLM of ammonia (NH 3 ) and 3 SLM of H 2 diluent. Into the single crystalline GaN-layer we have implanted radioactive "6Tm and 19 6yb at room temperature with an ion energy of 60 keV and a dose of 2 1013 cm-2 . These implantations were done at the ISOLDE facility at CERN [15]. TRIM simulations gave a mean ion range of 15.8 nm (FWHM = 5.6 nm) and a peak concentration of about 1.4.1019 cm-3 for both isotopes [16]. Two samples were implanted with oxygen prior the radioactive implantation. The ion energy was set to 13 keV so that both implantation profiles have a maximum overlap. The implantation dose of oxygen was 4 1014 cm"2 yielding into a ten times larger peak concentration of 1.4 1020 cm" 3. However, the damage introduced by the oxygen implantation and by the rare earth implantation are comparable [16]. The lattice sites of the implanted 167Tm and 169Yb atoms were determined with the emission channeling technique (EC) [12,13]. Emitted decay particles such as conversion electrons, Bparticles or a-particles were channeled along low-index crystal directions, leading to anisotropic emission distributions. The emission yield as a function of emission angle with respect to a given crystal axis or plane depends in a characteristic way on the lattice sites occupied by the emitter atoms. In the case of 167Tm and 169 Yb channeling effects of emitted conversion electrons were measured. Fig. 1 shows the simplified decay schemes of 167Tm and 169Yb. 167Tm decays by electron capture mainly into an excited state of 167 mEr with a half-life of 2.27 s (fig. 1,left). The 200 keV conversion electrons emitted in the subsequent decay process were utilized for the lattice site determination of Er. However, the Er site is determined by the lattice site of the mother nucleus 167TTm, because the low recoil energy of 1.8 eV during the electron capture decay process is not sufficient to displace the Er atom. Furthermore, we expect that both rare earth elements occupy the same lattice site due to their very similar valence electron configuration. The isotope 169Yb decays by electron capture (recoil energy 2.6 eV) into two exited states of 169Tm with half-lives of 0.1 ns and 0.66 Jis, respectively. Several conversion electron lines with energies around 118 and 138 keV after the electron capture decay process were used in the EC measurements. The samples were pre-oriented by Laue X-ray photographs and mounted on a three-axis goniometer in a vacuum chamber. The emitted electrons were detected with a silicon surface barrier detector. The implantation spot of 3 mm diameter, the de

Data Loading...