Instability of amorphous oxide semiconductors via carrier-mediated structural transition between disorder and peroxide state

Abstract

The excited holes occupying the valence band tail (VBT) states in amorphous oxide semiconductors (AOS) are found to induce formation of meta-stable O-2(2-) peroxide defects. The VBT states are at least partly characterized by the O-O pp sigma* molecular orbital, and the localized-hole-mediated lattice instability results in the formation of the peroxide defects. Along with the O-O bond formation, the pp sigma* state is heightened up into the conduction bands, and two electrons are accordingly doped in the electronic ground state. The energy barrier from the O-2(2-) peroxide state to the normal disorder state is found to be 0.97eV in hybrid density functional theory. The hole-mediated formation of the meta-stable peroxide defects and their meta-stability is suggested as an origin of the negative bias and/or illumination stress instability in AOS.