Energy Levels of Impurities in SiC

Polytype Stacking sequence Number of inequivalent sites  

The ionisation energies of the electronically active impurities have been determined primarily by photoluminescence techniques and Hall measurements. Ionisation energy levels of such impurities as nitrogen and some of the group III elements (aluminium, gallium, boron) in 3C-, 4H-, 6H- and 15R-SiC polytypes are compiled in TABLE 2. Nitrogen gives relatively shallow donor levels. In contrast, other p-type dopants have deep-level acceptor states. 

Segall et al [21] performed Hall measurements on n-type 3C-SiC epitaxial films and made detailed analyses of the temperature-dependent carrier concentrations. They found that the donor ionisation energy ED depends on the donor concentration ND with the relation ED(ND) = 48-2.6x 10 5ND1/3meV. A similar dependence was observed by Lomakina et al [22] for n- and p-type 6H-SiC. 

The optical activation energy of boron is about 0.7 eV [3,23], in contrast to the thermal activation energy of 0.39 eV [22] calculated from the temperature dependence of the Hall mobility. This difference was discussed by Veinger et al [24]. They found, from Hall and ESR measurements, that the deeper level is an activator for the high-temperature luminescence but not seen in the ESR spectra and that the shallow level is a paramagnetic state. 

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Energy levels of impurities in SiC C NITROGEN AND GROUP III ELEMENT IMPURITIES... 

In this Datareview, we concentrate on deep levels measured by capacitance and admittance techniques those measured by other techniques are detailed in Datareview 4.1. For completeness, trap parameters for major defects and impurities obtained from all techniques are listed. Capacitance techniques have proven useful for the characterisation of deep states in semiconductor devices. In particular, states which are non-radiative can be analysed by this technique. If the state under study is one which principally determines the conductivity of the crystal, the techniques of admittance spectroscopy are used. The set-up for doing capacitance and admittance spectroscopy on SiC is identical to that used for other semiconductors with the exception of the necessity to operate the system at higher temperatures in order to access potentially deeper levels in the energy gap. The data are summarised in TABLE 1. 

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