Oxygen '96
Early Stages of Oxygen Precipitation in Silicon
MAGNETIC RESONANCE INVESTIGATIONS OF THERMAL DONORS IN
SILICON
C. A. J. Ammerlaan, Yu. V. Martynov, I. S. Zevenbergen
and T. Gregorkiewicz
Van der Waals-Zeeman Institute, University of Amsterdam,
Valckenierstraat 65, NL-1018 XE Amsterdam, The Netherlands
silicon, oxygen, hydrogen, shallow thermal donors,
magnetic resonance
Heat treatment of oxygen-rich silicon in the temperature range 450-500
degrees C for times ranging from minutes to several hundreds of hours
produces centres with donor activity. By the method of electron
paramagnetic resonance (EPR) two prominent spectra, labelled Si-NL8
and Si-NL10, respectively, were observed and were associated to
paramagnetic states of these centres. On the basis of angular
dependent resonance patterns the centres were described with g tensors
of orthorhombic-I symmetry. Introducing the 17-oxygen isotope and
applying electron nuclear double resonance (ENDOR) the presence of
oxygen atoms in both centres was established; the oxygen atoms are
located on one of the mirror planes of the 2mm symmetry group. From
ENDOR on the ligand 29Si nuclei the wave function
describing the electron with unpaired spin was found to be quite
extended; this is consistent with a shallow character of the donor
state. Both centres appear to exist in a large number of
configurations, up to 17 have been reported, the versions with smaller
binding energy and more isotropic g tensor developing upon increase of
the heat-treatment time. These very similar, but yet distinct,
configurations are not resolved in EPR at standard frequencies, only a
continuous shift of the overall g tensor parameters is observed.
For the spectrum Si-NL8 the model of a singly ionised shallow double
oxygen-related donor is generally accepted; contrary to this, the
situation with spectrum Si-NL10 remained more puzzling. The two main
difficulties are, firstly, the existence of two different families of
heat-treatment centres with very similar properties and, secondly, the
observation of distinct 27Al ENDOR interactions in the
Si-NL10 spectrum together with the observation of Si-NL10 centres in
silicon with definitely no aluminium present.
Recently, a prominent role of hydrogen in the formation of Si-NL10
centres has been discovered. Hydrogen hyperfine interactions were
detected by ENDOR and further studied by field-scanned ENDOR. In
deuterium-doped material the quadrupole interaction of the local
electric field gradient with the deuteron was measured. The direction
of the hydrogen bond was found to be parallel to the <011> crystalline
axis perpendicular to the oxygen-containing plane of the thermal
donor. It also appeared that the true symmetry of this centre is
triclinic, i.e., lower than the orthorhombic symmetry as resolved in
the EPR. On this basis an identification of the Si-NL10 centre as a
singly hydrogen-passivated thermal donor in its neutral charge state
is proposed. It appears necessary to distinguish between
aluminium-containing centres, Si-NL10(Al), and hydrogen-containing
ones, Si-NL10(H). Infrared absorption spectra as reported in the
literature, and related to so-called shallow thermal donors (STD's),
are probably due to these Si-NL10 centres.
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Last modified: Sat Mar 16 18:06:15 GMT 1996
JG
