Local electronic structure of dilute hydrogen in β-Ga2 O3 probed by muons

The local electronic structure of muons (Mu) as dilute pseudohydrogen in single-crystalline β-Ga2O3 has been studied by the muon spin rotation/relaxation (μSR). High-precision measurements over a long time range of ∼25μs have clearly identified two distinct Mu states: a quasistatic Mu (Mu1) and fast-moving Mu (Mu2). 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 Mu1 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 Mu2 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-⇄Mu0+e-).