Effects of hole self-trapping by polarons on transport and negative bias illumination stress in amorphous-IGZO

TL;DR

This study uses first-principles calculations to analyze how hole self-trapping by polarons affects transport and NBIS in amorphous-IGZO, revealing high self-trapping energies and peroxide formation as key factors.

Contribution

It provides a detailed atomic-level understanding of hole trapping, peroxide formation, and their roles in NBIS in amorphous-IGZO, which was not previously well-characterized.

Findings

Holes are captured as polarons with high self-trapping energies.

Localized holes promote peroxide formation, linked to NBIS.

Hydrogen facilitates hole diffusion and trapping.

Abstract

The effects of hole injection in amorphous-IGZO is analyzed by means of first-principles calculations. The injection of holes in the valence band tail states leads to their capture as a polaron, with high self-trapping energies (from 0.44 to 1.15 eV). Once formed, they mediate the formation of peroxides and remain localized close to the hole injection source due to the presence of a large diffusion energy barrier (of at least 0.6eV). Their diffusion mechanism can be mediated by the presence of hydrogen. The capture of these holes is correlated with the low off-current observed for a-IGZO transistors, as well as, with the difficulty to obtain a p-type conductivity. The results further support the formation of peroxides as being the root cause of Negative bias illumination stress (NBIS). The strong self-trapping substantially reduces the injection of holes from the contact and limits the creation of peroxides from a direct hole injection. In presence of light, the concentration of holes substantially rises and mediates the creation of peroxides, responsible for NBIS.