Negative-Udefect: Interstitial boron in silicon

Novel optical deep-level-transient-spectroscopy (DLTS) studies are reported which reveal a new level (the single-donor level) of interstitial boron in silicon located at $E_c$-(0.13±0.01) eV. Detailed studies of this level and the previously detected single-acceptor level at $E_c$-(0.37±0.08) eV establish that these levels lie in negative-U ordering. A large Poole-Frenkel effect in the DLTS observed emission rate is apparent, and when properly accounted for provides a direct and unambiguous connection to the EPR-identified interstitial boron atom.