Diluted II-VI Oxide Semiconductors with Multiple Band Gaps
We report the realization of a new multi-band-gap semiconductor. The highly mismatched alloy Zn1-yMnyOxTe1-x has 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 Zn1-yMnyTe host. When only 1.3% of Te atoms is replaced with oxygen in a Zn0.88Mn0.12Te crystal (with band gap of 2.32 eV) the resulting band structure consists of two direct band gaps with interband transitions at ~1.77 eV and 2.7 eV. This remarkable modification of the band structure is well described by the band anticrossing model in which the interactions between the oxygen-derived band and the conduction band are considered. With multiple band gaps that fall within the solar energy spectrum, Zn1-yMnyOxTe1-x is a material perfectly satisfying the conditions for single-junction photovoltaics with the potential for power conversion efficiencies surpassing 50%.