On The Origin of Visible Luminescence from SIO 2 Films Containing Ge Nanocrystals
- PDF / 1,156,503 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 6 Downloads / 198 Views
Mat. Res. Soc. Symp. Proc. Vol. 405 0 1996 Materials Research Society
effect of deuterium on PL all strongly suggest that the visible PL is primarily due to luminescent defect centers in the matrix or at the nanocrystal/matrix interface. II. ION BEAM SYNTHESIS OF S10 2 FILMS CONTAINING GE NANOCRYSTALS SiO 2 films, 100 nm thick, grown by wet thermal oxidation on a lightly p-doped (100) Si wafers were implanted at room temperature with 70 keV 74Ge+ at doses of lxlO' 6/cm 2, 2x10 16/cm 2 , and 5xl0' 6/cm 2 . The energy was chosen such that the implanted Ge concentration profile is completely within the oxide film, with the peak concentration lying 30-40 nm from the surface. For the three implantation, doses, the peak concentrations are 3, 6, and 13 at.% Ge, respectively, as determined by Rutherford backscattering spectrometry. After implantation, the samples were annealed in high vacuum at 600'C, 800'C, and 1000°C for 40 min. We have previously performed extensive transmission electron microscopy (TEM) characterization on these samples and the average nanocrystal sizes were determined from Gaussian fits to the size distributions [8]. For the 6 at.% Ge samples, the average sizes are 1.9 nm, 3.2 nm, and 7.2 nm, with full-widths at half-maximum of 1.5 jim, 3.4 am, and 4.0 nm, for the samples annealed at the three temperatures, respectively. III. PHOTOLUMINESCENCE AND LIFETIME MEASUREMENTS OF SIC 2 FILMS CONTAINING GE NANOCRYSTALS Photoluminescence spectra were taken with 100 mW/mm2 excitation using 457.9 nm Ar+ laser radiation, detected with an InGaAs photomultiplier and a grating spectrometer with a spectral resolution of 3.2 nm. The sample temperature was controlled between 12 K and 300 K by a closed-cycle He cryostat. All spectra have been corrected for the photomultiplier and grating efficiencies. Figure l(a) shows the room temperature PL spectra of the 6 at.% Ge sample, asimplanted and annealed at different temperatures. Several notable characteristics of the PL spectra in Fig. 1(a) have also been reported previously for SiO 2 containing Ge nanocrystals synthesized by other methods [2-7]. First, only a weak PL signal is observed for the unannealed sample compared to the annealed samples. Second, the annealed samples show an intense PL signal, visible to the unaided eye, with characteristically broad spectra. Third, no appreciable shift in peak luminescence energy is observed with variation in the annealing temperature (i.e., nanocrystal size). Figure 2 shows a plot of the peak luminescence energy of the measured PL spectra as a function of nanocrystal diameter for the same set of samples as in Fig. l(a). The horizontal and vertical error bars indicate the FWHM of the nanocrystal size distributions and PL spectra, respectively. For comparison, a calculated variation of exciton transition energy as a function of the quantum dot diameter is also shown [9]. High resolution TEM images of the samples with the smallest and the largest nanocrystals are shown as insets in Fig. 2. For the nanocrystal size range in our sampl
Data Loading...
