Local electronic structure of dilute hydrogen in ${\hat{I}}^2$-Ga${}_2$O${}_3$ probed by muons

Abstract

The local electronic structure of muons (Mu) as dilute pseudo-hydrogen in single-crystalline ${\hat{I}}^2$-Ga${}_2$O${}_3$ has been studied by the muon spin rotation/relaxation ($\hat{I}¼$SR). High-precision measurements over a long time range of $\sim$25 $\hat{I}¼$s have clearly identified two distinct Mu states: a quasi-static Mu (Mu${}_1$) and fast-moving Mu (Mu${}_2$). By comparing this result with predictions from the recently established ambipolarity model, these two states are respectively attributed to the relaxed-excited states associated with the donor ($E^{+/0}$) and acceptor ($E^{-/0}$) levels predicted by density functional theory (DFT) calculations for the interstitial H. Furthermore, the local electronic structure of Mu${}_1$ is found to be an OMu-bonded state with three-coordinated oxygen. The structure is almost identical with the thermal equilibrium state of H, and it is found to function as an electron donor. The other Mu${}_2$ is considered to be in the hydride state (Mu${}^{-}$) from the ambipolarity model, suggesting that it is in fast diffusion motion through the short-lived neutral state due to the charge exchange reaction with conduction electrons (Mu${}^0+e^{-}\rightleftarrows$Mu${}^{-}$).

7 pages, 4 figures, plus Supplemental Material (3 pages, 6 figures)