Tailored electric and optical properties of Nd doped ZnO: from transparent conducting oxide to photon down-shifting thin films
Nd-doped ZnO films with highly tunable properties were grown by pulsed electron beam deposition at 500 °C on Si and c-cut single crystal substrates under oxygen gas. The effects of a slight change in the oxygen pressure (10−2 to 2 × 10−2 mbar) on the composition, structure and physical properties of the films were studied. Films grown at 10−2 mbar present a low resistivity (5 × 10−3 Ω cm) and high transparency in visible range and do not show any near-infrared emission due to Nd3+ ions. On the contrary, films grown at 2 × 10−2 mbar have high resistivity (>16 Ω cm), high optical transparency and near infrared emission of the Nd3+ ions is observed under indirect excitation at 335 nm (i.e. absorption by the ZnO matrix and transfer to Nd3+ ions). These significant changes in physical properties, leading from transparent conducting oxide to photon down-shifting thin films, are related to growth mode in pulsed-electron beam deposition.