Instability of Amorphous Oxide Semiconductors via Carrier-Mediated Structural Transition between Disorder and Peroxide State

TL;DR

This paper investigates how excited holes induce formation of peroxide defects in amorphous oxide semiconductors, leading to structural instability and potential device degradation.

Contribution

It reveals a hole-mediated mechanism for peroxide defect formation and quantifies the energy barrier using hybrid density functional theory.

Findings

Peroxide defects are formed via localized-hole-induced lattice instability.

The energy barrier from peroxide to normal state is 0.97 eV.

Peroxide defect formation explains bias and illumination stress instability.

Abstract

The excited holes occupying the valence band tail states in amorphous oxide semiconductors are found to induce formation of meta-stable O$_2^{2-}$ peroxide defects. The valence band tail 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 0.97 eV 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 amorphous oxide semiconductors.