Nitrogen-Carbon Interactions in Optical Defects in Silicon
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NITROGEN-CARBON INTERACTIONS IN OPTICAL DEFECTS IN SILICON
A. DtRNEN* , R. SAUER** , AND G. PENSL*** * Physikalisches Institut (Tell 4), Universitdt Stuttgart, of ** of *** of
Federal Republic
Germany Max-Planck-Institut fur Festkbrperforschung, Stuttgart, Federal Republic Germany Institut fUr Angewandte Physik, Universit~t Erlangen, Federal Republic Germany
ABSTRACT We report five photoluminescence lines NI through N5 in silicon which emerge after sequential nitrogen and carbon implantation. Studied is in particular the 0.7456 eV (NI) electronic-vibronic spectrum. Single nitrogen and carbon atoms in the defect are identified by isotope shifts of the nophonon transition and of a local mode satellite with vibration quantum energy tw- 122.9 meV. Uniaxial stress or Zeeman measurements yield monoclinic I (Clh) or trigonal (C3v) symmetry, respectively, of the optical defect. Comparing the energy of the local mode and its isotope effects with recent literature data on the nitrogen 963 cm-I IR vibrational absorption line we discuss a defect model involving a substitutional nitrogen atom modified by an interstitial carbon atom.
Murakami et al. [11 recently reported a photoluminescence line at 0.746 eV in nitrogen implanted pulsed-laser annealed silicon and ascribed it to neutral nitrogen on a substitutional site. A second line at 0.767 eV emerging in the same crystals was also associated with nitrogen. In the present work we observe both lines along with three other new lines under different production conditions using combined nitrogen and carbon implantations. In the case of the 0.7456 eV (Ni) line studied here in detail we demonstrate that the optical defect incorporates single nitrogen and carbon atoms implying that all of the lines may be due to similar nitrogen-carbon interactions. A partial account of our data on the NI defect has very recently been given elsewhere [21. Fig. I shows the electronic-vibronic spectrum of the NI line at 0.7456 eV. Several vibronic sidebands (TA, LA, TO, OF) are due to the coupling of lattice phonons. The OF replica is denotedly narrower and much more intense than expected for a cure lattice mode. Hence, we refer to this replica as a defect modified O phonon or local mode (LM)I. Additional low energy structure is assigned to defect local modes (LM2 with tf = 71.3 meV and LM7 with i=cu 122.9 meV) or to combination bands: Line Line Line Line
3 4 5 6
Or TA Or o0
+ + + +
TA LM2 LA(a) LA
Line 8 Line 9 Line 10
2xO0 Or + LM2 Or + TA
Up to 2.5 pm, no other structure than that shown in Fig. 1 was observed. The NI line exhibits an associated higher energy transition NI* (indicated but not resolved in Fig. 1) at an excess energy of 4.7 meV. NI* and Ni thermalize with an activation energy of 4.8 meV, hence NI * is a transition from an excited upper state to the same ground state as in the NI transition [2].
Mat.Res. Soc. Symp.Proc. Vol.59. @1986 Materials Research Society
546
2
N1 (0.746eV) Spectrum T=4.2 K
r
S6 .00
N2
TA 7
T]
LA
9
C 0
1 6(a
0 0 r-C
1.8
2.0
Wavelength X
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