Ground state of ultrashallow thermal donors in silicon

Abstract

We have found ultrashallow thermal donors (USTDs) in carbon- and hydrogen-doped Czochralski silicon (CZ-Si) crystals, in which the electronic structure obeys the effective-mass theory. To the best of our knowledge, these are the shallowest energy levels among those of the currently reported donors in Si crystals. In addition, the ground state (1s state) of USTDs was found to be split into at least two. In this study, we measured the temperature dependence of the transmittance induced by the transition from the ground state or upper ground state to the 2p+− and 2p0 states of USTD-1 and USTD-3. It was found that the energy levels of the upper ground state of USTD-3 are shallower than those of USTD-1 despite the fact that the ground state of USTD-1 is shallower than that of USTD-3. That is, the energy levels of the upper ground state of USTD-1 and USTD-3 are inverted against those of the ground state. In addition, we compared the electron spin resonance of 13C (nuclear spin I = 1/2)- and deuterium (I = 1)-doped Si with that of 12C (I = 0)- and hydrogen (I = 1/2)-doped Si. However, no clear difference was found between the electron spin resonance spectra of the two. On the basis of these results, we briefly discuss the atomic structure of the USTDs.