The vacancy donor pair in silicon, germanium and SiGe alloys

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The vacancy donor pair in silicon, germanium and SiGe alloys Powered By Docstoc
					         High resolution DLTS of vacancy-donor pairs
                 in P, As and Sb doped silicon
F. D. Auret1,2, A. R. Peaker2, V. P. Markevich1,3, L. Dobaczewski4, R. M. Gwilliam 5
        Department of Physics, University of Pretoria, Pretoria 0002, South Africa.
        Centre for Electronic Materials Devices and Nanostructures, University of
                     Manchester, PO Box 88, Manchester, M601QD, UK
            Institute of Solid State and Semiconductor Physics, Minsk, Belarus.
                              Institute of Physics, Warsaw, Poland
                    Ion Beam Centre, University of Surrey, GU2 7XH, UK

Keywords: Silicon, irradiation defects, donor-vacancy complex, Laplace DLTS

        Achieving very high n-type doping levels in silicon has recently prompted
renewed interest in donor-related defects, e.g. the donor-vacancy complexes (E
centres) and necessitated an understanding of their electronic and thermal behaviour.
We report results from an experiment designed to characterise, by high resolution
(Laplace) DLTS, the electronic properties of radiation induced E-centers in Si
associated with phosphorous, antimony and arsenic. The E-centres have been
introduced by electron radiation. Four sets of samples were used: the first sample
contained only P, the second one was co-doped with P and Sb, the third was co-doped
with P and As, while the fourth sample contained P, Sb and As. In the sample
containing only P, the activation energy of electron emission from the single acceptor
level of V-P in silicon was found to be (0.4580.005) eV. For the sample with P and
Sb, the Laplace peaks of the V-Sb and V-P were clearly separated and the ratio of
their emission rates, r, was always > 4. The energy levels extracted were
(0.4010.010) eV and (0.4440.010) eV for the V-Sb and V-P, respectively. The
levels calculated for V-P in these two samples can be considered to be, within the
experimental error, the same. In the sample with As and P, the ratio of the emission
rate of V-As to V-P was 1.8, i.e below the value of 2 which is normally necessary for
reliable peak separation. The result was that, although the V-As and V-P L-DLTS
peaks could clearly be split, there is an uncertainty in their calculated energy level
positions of (0.4350.005) and (0.4340.010) eV, respectively. In the sample
containing all three dopants, the L-DLTS peak of Sb could be clearly distinguished
from those of the P and As but the level of V-Sb was found to be (0.376 0.010) eV,
significantly lower than in the sample containing only P and As. Similarly, the levels
found for the V-P and V-As, (0.4130.010) eV and (0.3980.010) eV, were also
lower as where only two of the E-centers were present. The results presented clearly
demonstrates the remarkable resolving power of Laplace DLTS for closely spaced
levels. At the same time it should noted that the results obtained when the ratio of the
emission rates of levels is below two are not quantitatively reliable.

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