Hydrogen states in hydrogen-passivated semiconducting barium disilicide measured via muon spin rotation

Passivation of BaSi2 films is essentially important for their use in solar cell applications. We study the effect of atomic H on photoresponsivity enhancement of 0.5-μm-thick BaSi2 films. A H supply duration of 15 min enhances the photoresponsivity of the BaSi2 film by a factor of 10. We also investigate the electronic states of H in BaSi2 via muon spin rotation. An implanted muon (Mu+) beam binds electrons to form muonium (Mu+e−). Their response to thermal activation shows that Mu+e− accompanies a shallow energy level of approximately 31 meV below the conduction band minimum (CBM), indicating that atomic H also serves as an electronically active donor impurity in BaSi2. This result is in good agreement with ab initio studies showing that a localized half-filled peak appears approximately 40 meV below the CBM if the first neighbors of the H atom are one Si atom and one Ba atom.