Electronic structure of interstitial hydrogen in In-Ga-Zn-O semiconductor simulated by muon

TL;DR

This study investigates the local electronic structure of interstitial muons in In-Ga-Zn-O semiconductors using $bcm$SR experiments and DFT calculations, revealing muon sites and charge states related to hydrogen behavior.

Contribution

The paper combines $bcm$SR experiments with DFT calculations to identify muon sites and charge states in IGZO, providing new insights into hydrogen's role in this semiconductor.

Findings

Mu occupies Zn-O bond-center sites similar to crystalline ZnO.

Mu acts as an electron donor in c-IGZO and amorphous IGZO.

Heavily hydrogenated a-IGZO shows inhomogeneous Mu distribution indicating complex states.

Abstract

We report on the local electronic structure of interstitial muon (Mu) as pseudo-hydrogen in In-Ga-Zn oxide (IGZO) semiconductor studied by muon spin rotation/relaxation ($\mu$SR) experiment. In polycrystalline (c-) IGZO, it is inferred that Mu is in a diamagnetic state, where the $\mu$SR time spectra under zero external field is perfectly described by the Gaussian Kubo-Toyabe relaxation function with the linewidth $\Delta$ serving as a sensitive measure for the random local fields from In/Ga nuclear magnetic moments. The magnitude of $\Delta$ combined with the density functional theory calculations for H (to mimic Mu) suggests that Mu occupies Zn-O bond-center site (Mu$_{\rm BC}$) similar to the case in crystalline ZnO. This implies that the diamagnetic state in c-IGZO corresponds to Mu$_{\rm BC}^+$, thus serving as an electron donor. In amorphous (a-) IGZO, the local Mu structure in as-deposited films is nearly identical with that in c-IGZO, suggesting Mu$_{\rm BC}^+$ for the electronic state. In contrast, the diamagnetic signal in heavily hydrogenated a-IGZO films exhibits the Lorentzian Kubo-Toyabe relaxation, implying that Mu accompanies more inhomogeneous distribution of the neighboring nuclear spins that may involve Mu$^-$H$^-$-complex state in an oxygen vacancy.