Doping efficiency and optical and electrical properties of the N-doped ZnO films grown on c-sapphire were investigated. An anomalous Raman mode at 275 cm−1 was observed in the films grown at high Zn temperature, which implied that the films have a large number of defects induced by high N concentration. The intensity ratio of the donor-acceptor pair (DAP)/donor-bound exciton (DX) increases with increasing Zn temperature; this was attributed to the increase of N concentration. The films exhibit a conversion from n-type to p-type conductivity with increasing Zn temperature, and reproducible p-type conductivity was obtained at the Zn temperature of 255 °C. This study offers a simple and effective route to enhance the N solubility in ZnO films and confirms that the anomalous Raman mode at 275 cm−1 was related to substitution of N for O site (NO) and not related to substitution of N2 for O site (N2)O.

The transport properties of single-stranded DNA ͑ssDNA͒ wrapped single-walled carbon nanotubes ͑SWNTs͒ are studied from low to room temperature. Atomic force microscopy reveals a regularly patterned geometry of ssDNA molecules on the surface of SWNTs. Our measurements indicate that the semiconducting behavior of SWNTs is drastically changed after ssDNA modification, showing a clear charge-transfer process at room temperature. At low temperatures single-electron tunneling features are observed up to 80 K, demonstrating clearly that quantum dots in series are created in the SWNTs due to the ssDNA wrapping.