Native defects at the Si/SiO₂ interface-amorphous silicon revisited

We review here work which demonstrates that silicon dangling bonds, Si₃, are the predominant, electrically active deep states associated with the clean crystalline silicon/amorphous SiO₂ interface. Si₃ exists in three charge states in the silicon band gap with E_{+,0 {reversed tilde equals} Ev + 0.3 eV} and E_0,- {reversed tilde equals} E_v + 0.9 eV, where E represents a demarcation level between charge states. We discuss the structural and electronic characteristics of Si₃ at the Si/SiO₂ interface, including degree of charge localization, effective correlation energies, role of hydrogen passivation, etc. We argue, from the strongly analogous behavior in amorphous silicon, that the electronic density of states in the gap is dominated by the characteristic effects of disorder in covalently bonded semiconductors. The states consist of two topologically distinct entities: distorted, fully-bonded network configurations giving rise to shallow silicon band tails, and three-fold coordinated, amphoteric silicon defects.