title: Continuously Controlled Optical Band Gap in Oxide Semiconductor Thin Films.
abstract: The optical band gap of the prototypical semiconducting oxide SnO2 is shown to be continuously controlled through single axis lattice expansion of nanometric films induced by low-energy helium implantation. While traditional epitaxy-induced strain results in Poisson driven multidirectional lattice changes shown to only allow discrete increases in bandgap, we find that a downward shift in the band gap can be linearly dictated as a function of out-of-plane lattice expansion. Our experimental observations closely match density functional theory that demonstrates that uniaxial strain provides a fundamentally different effect on the band structure than traditional epitaxy-induced multiaxes strain effects. Charge density calculations further support these findings and provide evidence that uniaxial strain can be used to drive orbital hybridization inaccessible with traditional strain engineering techniques.
authors.affiliation: Materials Science and Technology Division, ORNL , Bethel Valley Road, Oak Ridge, Tennessee 37831-6056, United States.
authors.forename: Andreas
authors.initials: A
authors.lastname: Herklotz
authors.affiliation: Renewable Energies Laboratory - Photovoltaics, National Institute for Research and Development in Electrochemistry and Condensed Matter , Timisoara 300569, Romania.
authors.forename: Stefania Florina
authors.initials: SF
authors.lastname: Rus
authors.affiliation: Materials Science and Technology Division, ORNL , Bethel Valley Road, Oak Ridge, Tennessee 37831-6056, United States.
authors.forename: Thomas Zac
authors.initials: TZ
authors.lastname: Ward
keywords: Strain doping; ellipsometry; helium ion implantation; tin oxide; uniaxial strain