Diluted II-VI Oxide Semiconductors with Multiple Band Gaps
We report the realization of a new mult-band-gap semiconductor. ${\mathrm{Z}\mathrm{n}}_{1\ensuremath{-}y}{\mathrm{M}\mathrm{n}}_{y}{\mathrm{O}}_{x}{\mathrm{T}\mathrm{e}}_{1\ensuremath{-}x}$ alloys have been synthesized using the combination of oxygen ion implantation and pulsed laser melting. Incorporation of small quantities of isovalent oxygen leads to the formation of a narrow, oxygen-derived band of extended states located within the band gap of the ${\mathrm{Z}\mathrm{n}}_{1\ensuremath{-}y}{\mathrm{M}\mathrm{n}}_{y}\mathrm{T}\mathrm{e}$ host. When only 1.3% of Te atoms are replaced with oxygen in a ${\mathrm{Z}\mathrm{n}}_{0.88}{\mathrm{M}\mathrm{n}}_{0.12}\mathrm{T}\mathrm{e}$ crystal the resulting band structure consists of two direct band gaps with interband transitions at $\ensuremath{\sim}1.77$ and 2.7 eV. This remarkable modification of the band structure is well described by the band anticrossing model. With multiple band gaps that fall within the solar energy spectrum, ${\mathrm{Z}\mathrm{n}}_{1\ensuremath{-}y}{\mathrm{M}\mathrm{n}}_{y}{\mathrm{O}}_{x}{\mathrm{T}\mathrm{e}}_{1\ensuremath{-}x}$ is a material perfectly satisfying the conditions for single-junction photovoltaics with the potential for power conversion efficiencies surpassing 50%.