Site-Selective Photoluminescence Spectroscopy of Er-Implanted Wurtzite Gan Under Various Annealing Conditions
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Mat. Res. Soc. Symp. Proc. Vol. 512 © 1998 Materials Research Society
and how the recovery with increasing of multiple Er3÷ centers.
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of the ion implantation damage in GaN affects the PL
EXPERIMENTAL PROCEDURE The GaN films were grown on sapphire by atmospheric pressure MOCVD, and were implanted with a dosage of 4 X 1013 Er ions/cm 2 at 280 keV [1-3]. The implanted sample was annealed in a conventional tube furnace at temperatures ranging from 400 to 1000 TC for 90 minutes under a continuous flow of nitrogen gas [5-6]. 6K PL spectroscopy was carried out on the Er-implanted GaN annealed at seven different temperatures in the 400 to 1000 TC range. The PL spectra were excited by a variety of sources including a tunable titanium-doped sapphire laser, a HeNe laser, an Ar ion laser, a Xe lamp
dispersed by a double grating monochromator, and a HeCd laser. After finishing a complete set of PL experiments in the sample annealed at lower temperature, the same sample was annealed at higher temperature. The luminescence was analyzed by a 1-m single grating monochromator and detected by a cooled Ge PIN detector. Samples were cooled to liquid helium temperature in a Janis Supervaritemp Cryostat. RESULTS AND DISCUSSION Figure 1 shows the 6K PL spectra in the - 0.73 - 1.2 eV spectral range obtained from an Er-implanted film of GaN annealed at temperatures in the 400 to 1000 °C range. All the PL spectra excited by 515 nm light exhibit the sharply structured 1540 nm band characteristic of the 4113/2 _- 4115/2 transitions of Er3 and the broad defect PL bands peaking at 1200 and 1270 nm on which the Er-related PL band is superimposed [1]. The 515 nm pumping line is marked by an arrow on the strong absorption band peaking at 2.35 eV in the PLE spectrum (Fig. 2a) detected at the -1.04 eV peak position of the highest intensity in the broad-band damage-induced emission in the sample annealed at 900 TC in Fig. 1. The 2.35 eV PLE band in this PLE spectra appears to excite a mixture of some Er 3+ PL spectra from Er 3+-defect or -impurity complex sites as well as the damage-induced broad-band PL [4]. The excitation of some Er 3+-defect complex PL spectra (see Fig. 3) by pumping light within this band is due to the overlapping of some broad PLE bands (shown in Fig. 2b) which selectively excite these Er 3÷PL spectra. The broad defect PL bands seen in the PL spectra of the sample annealed at temperatures higher than 600 °C (Fig. 1) were suggested previously to be related to ion-implantation induced damage [1,4]. This assignment was based on the observations that the PL spectrum from Cr- (or Nd-) implanted samples of the same GaN film annealed at 900 °C (or 1000 'C) for 30 minutes shows the same broad defect PL band as obtained from an Er-implanted sample annealed under the same annealing condition [1] and that these defect PL bands are not seen in unimplanted samples annealed under the same annealing condition. Nearly identical defect PL bands were also reported by Silkowski et al. for Er- and Nd-implanted films of GaN annealed at 1000 °C
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