Thermal donors

A comparison of the deuterium profile measured by SIMS and the spreading resistance profile obtained on deuterated samples is shown in Fig. 6. The region over which there is a reduction in thermal donor concentration matches well with the depth of deuterium incorporation. There is an excess of deuterium over the amount needed to passivate all the oxygen-donor centers. This is frequently observed in hydrogenation experiments and indicates there is hydrogen present in several states. 

Fig. 5. Capacitance and current transient spectra from -type, CZ grown Si annealed for 18h at 450°C to form the shallow, oxygen thermal donors. (Chantre et al., 1987). Hydrogenation at 200°C passivates the electrical activity of these thermal donors (Chantre et at, 1987).

These may include atomic and molecular hydrogen, as well as hydrogen bonded at oxygen-related clusters. Passivation of the 450°C thermal donors has also been investigated as a function of cluster size by Johnson and Hahn (1986) and Johnson et al. (1986). 

Fig. 6. Spreading resistance and SIMS profile from deuterated CZ Si containing an initial uniform concentration of 6 x 1016 cm-3 thermal donors. The high, near-surface concentration is due probably to deuterium molecule formation (Pearton et al., 1986). 

Benko G., Kallioinen J., Korppi-Tommola J. E. I., Yartsev A. P. and Sundstrom V. (2002), Photoindueed ultrafast dye-to-semieonductor electron injection from nonthermalized and thermalized donor states , J. Am. Chem. Soc. 124,489 93. 

We are faced with two interconnected problems related to the intelligibility of the presentation. The first one concerns the nomenclature of the centres other than isolated atoms and the second the labelling of the optical transitions. These problems are not trivial, [5], but not as severe for H-like centres as for deep centres. The different notations for the shallow thermal donor complexes in silicon, discussed in Sect. 6.4.2, are however, a counter-example of this statement. In this book, on the basis of the present knowledge, names of centres, in direct relation with their atomic structure, have been privileged, but the usual label has however been indicated. When the exact structure is not simple and when there exist an acronym, like TDD for thermal double donor , it has been used. The labelling by their excited states of the transitions of the shallow donor centres and of similar species, whose spectra... 

When the line positions come from two sources, the spacing is measured from the same source. The 3p i — 2po spacing is included because it allows comparisons with donor centres where the 2p i line is split, as in the oxygen thermal donor spectra t Resonant phonon broadening of 2po, a [118], b [21]... 

A centre, called the a trap in connection with the study by Haynes and Hornbeck [98], has been reported to be the first TDD species, but without giving data on its ionization energies [159]. The electronic properties of this centre, labelled BTD-a for bistable thermal donor, or alternatively TDDO, have remained elusive for some time and they will be discussed with the metastability properties of the TDDs. To avoid any confusion in the following, the ionization energies of the different TDDs in the neutral and singly-ionized states are listed in Table 6.23. Apparently, no data have been reported for TDDi+ above TDD9. 

A thermal donor denoted TDD7, with an ionization energy of 55.8 meV when neutral, has been added to this list by Emtsev et al. [58]. The ratio E +/E o varies from 2.25 for % = 1 and stabilizes to 2.19 for i = 7, close to the EM ratio 2.21 for He-like donors. As the energy spans of the parity-allowed... 

The possibility of passivation of the TDDs by hydrogen has been investigated, but this point and the results obtained by optical spectroscopy will be discussed in the next section, with the properties of the shallow thermal donors. 

The observation of the metastability of TDD2 requires further production of thermal donors to raise the Fermi level position. The limiting value of Ep is Ec — 0.25 eV at room temperature and for samples with Ep in this energy region, partial metastability of TDD2 may be observed, as in Fig. 6.28. 

Fig. 6.32. Metastability effects of the neutral thermal donor spectra (2po lines) between 8.9 and 12.4 meV observed in three O-doped germanium samples with free-carrier concentrations increasing from (a) to (c) (see text). The spectra denoted 1 are obtained after cooling-down from RT under TEC and those denoted 2 after cooling-down under band-gap light illumination (after [47])...

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