DLTS investigation of the energy spectrum of Si : Mg crystals

Electrically active centers in $n$-type magnesium-doped silicon crystals are studied by deep-level transient spectroscopy (DLTS). Magnesium is introduced by diffusion from a metal film on the surface at 1100$^{\circ}$C. It is found that two levels with a similar concentration of $\sim$6 $\times$ 10$^{14}$ cm$^{-3}$ dominate in the DLTS spectrum; the value approximately corresponds to the interstitial magnesium (Mg$_ i$) concentration expected from diffusion conditions and published data on the Hall effect. The dependence of the electron emission rate from these levels on the electric-field strength agrees qualitatively with the Poole–Frenkel effect, which indicates the donor nature of both levels, although the absolute value of the effect differs from theoretical value. The activation energies of these levels found by the extrapolation of emission rates measured at various temperatures to zero field are 112 and 252 meV, which coincides within the accuracy with energies of ground states of the first and second donor levels of Mg determined previously from optical absorption. Thus, it is shown that when using high-quality initial material and the selected diffusion mode, interstitial magnesium atoms are the dominant centers with levels in the upper half of the band gap.