Stephane Aouba

High-temperature ferromagnetism in Mn-doped ZnO nanowires

We have observed ferromagnetism in dilute (∼1–4at.%) Mn-doped crystalline ZnO nanowires at temperatures up to 400K. Arrays of freestanding single crystal ZnO:Mn nanowires were fabricated by Au-catalyzed vapor-liquid-solid growth. Structure and compositional analyses revealed that Mn was incorporated into the ZnO lattice. From the observed saturation magnetization, the magnetic moment per Mn atom is estimated to be between 0.3μB and 1.2μB. Photoluminescence measurements show a strong suppression of defect related midgap emission, indicative of an interplay between Mn doping and native point defects.

Electrical properties of Ohmic contacts to ZnSe nanowires and their application to nanowire-based photodetection

Multilayer Ti∕Au contacts were fabricated on individual, unintentionally doped zinc selenide nanowires with 80nm nominal diameter. Four-terminal contact structures were used to independently measure current-voltage characteristics of contacts and nanowires. Specific contact resistivity of Ti∕Au contacts is 0.024Ωcm2 and intrinsic resistivity of the nanowires is approximately 1Ωcm. The authors have also measured the spectral photocurrent responsivity of a ZnSe nanowire with 2.0V bias across Ti∕Au electrodes, which exhibits a turnon for wavelengths shorter than 470nm and reaches 22A∕W for optical excitation at 400nm.

Electron transport in degenerate Mn-doped ZnO nanowires

The authors have performed variable-temperature electrical measurements on individual single-crystalline, Mn-doped ZnO nanowires. Using a back-gated field-effect transistor structure fabricated with electron-beam lithography, they have established that nanowires exhibit n-type conduction. At a temperature of 225K, the field-effect mobility and free electron concentration are ≈35cm2V−1s−1 and ≈3.6×1017cm−3, respectively. Carrier concentration varies weakly with temperature down to 12K, signifying that the material is degenerate. Mobility decreases with decreasing temperature down to 12K, in a manner consistent with ionized impurity scattering in a degenerate semiconductor.