Carrier transport in polycrystalline ITO and ZnO Al II The Influence of grain barriers and boundaries

ITO and ZnO Al films have been deposited by magnetron sputtering from ceramic and metallic targets at different substrate temperatures and with different plasma excitation modes DC and RF 13.56 and 27.12 MHz . Temperature dependent conductivity and Hall measurements down to 50 K were used to determine the carrier concentrations ND and the Hall mobilities . From the ND dependences, which were fitted by a carrier transport model taking into account ionized impurity and grain barrier scattering, the trap densities at the grain boundaries were estimated. ITO films show much lower trap densities down to Nt amp; 8776;1.5.1012 cm 2, compared to Nt values up to 3.1013 cm 2 for ZnO Al films. The temperature dependent mobilities were fitted by a phenomenological model with a T independent term and a metal like contribution or a thermally activated part due to grain barrier limited transport. Seebeck coefficient measurements as a function of the carrier concentration give hints to different transport mechanisms in ITO and ZnO

Carrier transport in polycrystalline transparent conductive oxides A comparative study of zinc oxide and indium oxide

Highly doped indium tin oxide films exhibit resistivities ? as low as 1.2.10 4 ?cm, while for ZnO films resistivities in the range of 2 to 4.10 4 ?cm are reported. This difference is unexpected, if ionized impurity scattering would be dominant for carrier concentrations above 1020 cm 3. By comparing the dependences of the effective Hall mobility on the carrier concentration of ZnO and ITO it is found that grain barriers limit the carrier mobility in ZnO for carrier concentrations as high as 2.1020 cm 3, independently, if the films were grown on amorphous or single crystalline substrates. Depending on the deposition method, grain barrier trap densities between 1012 to 3.1013 cm 2 were estimated for ZnO layers. Also, crystallographic defects seem to reduce the mobility for highly doped ZnO films. On the other hand, for ITO films such an influence of the grain barriers was not observed down to carrier concentrations of about 1018 cm 3. Thus the grain barrier trap densities of ZnO and ITO are significantly different, which seems to be connected with the defect chemistry of the two oxides and especially with the piezoelectricity of zinc oxid

Self-organization of (001) cubic crystal surfaces

Self-organization on crystal surface is studied as a two dimensional spinodal decomposition in presence of a surface stress. The elastic Green function is calculated for a $(001)$ cubic crystal surface taking into account the crystal anisotropy. Numerical calculations show that the phase separation is driven by the interplay between domain boundary energy and long range elastic interactions. At late stage of the phase separation process, a steady state appears with different nanometric patterns according to the surface coverage and the crystal elastic constants

Origin of Ferromagnetism in nitrogen embedded ZnO:N thin films

Nitrogen embedded ZnO:N films prepared by pulsed laser deposition exhibit significant ferromagnetism. The nitrogen ions contained in ZnO confirmed by Secondary Ion Microscopic Spectrum and Raman experiments and the embedded nitrogen ions can be regarded as defects. According to the experiment results, a mechanism is proposed based on one of the electrons in the completely filled d-orbits of Zn that compensates the dangling bonds of nitrogen ions and leads to a net spin of one half in the Zn orbits. These one half spins strongly correlate with localized electrons that are captured by defects to form ferromagnetism. Eventually, the magnetism of nitrogen embedded ZnO:N films could be described by a bound magnetic polaron model.Comment: 7 pages, 6 figure

Physical properties of metal-doped zinc oxide films for surface acoustic wave application

Metal-doped ZnO [MZO] thin films show changes of the following properties by a dopant. First, group III element (Al, In, Ga)-doped ZnO thin films have a high conductivity having an n-type semiconductor characteristic. Second, group I element (Li, Na, K)-doped ZnO thin films have high resistivity due to a dopant that accepts a carrier. The metal-doped ZnO (M = Li, Ag) films were prepared by radio frequency magnetron sputtering on glass substrates with the MZO targets. We investigated on the optical and electrical properties of the as-sputtered MZO films as dependences on the doping contents in the targets. All the MZO films had shown a preferred orientation in the [002] direction. As the quantity and the variety of metal dopants were changed, the crystallinity and the transmittance, as well as optical band gap were changed. The electrical resistivity was also changed with changing metal doping amounts and kinds of dopants. An epitaxial Li-doped ZnO film has a high resistivity and very smooth surface; it will have the most optimum conditions which can be used for the piezoelectric devices

Flexible Indium-Tin Oxide Crystal on Plastic Substrates Supported by Graphene Monolayer

Flexible and crystallized indium-tin oxide (ITO) thin films were successfully obtained on plastic polyethylene terephthalate (PET) films with monolayered graphene as a platform. The highly crystalline ITO (c-ITO) was first fabricated on a rigid substrate of graphene on copper foil and it was subsequently transferred onto a PET substrate by a well-established technique. Despite the plasma damage during ITO deposition, the graphene layer effectively acted as a Cu-diffusion barrier. The c-ITO/graphene/ PET electrode with the 60-nm-thick ITO exhibited a reasonable sheet resistance of similar to 45 Omega sq(-1) and a transmittance of similar to 92% at a wavelength of 550 nm. The c-ITO on the monolayered graphene support showed significant enhancement in flexibility compared with the ITO/PET film without graphene because the atomically controlled monolayered graphene acted as a mechanically robust support. The prepared flexible transparent c-ITO/graphene/PET electrode was applied as the anode in a bulk heterojunction polymer solar cell (PSC) to evaluate its performance, which was comparable with that of the commonly used c-ITO/glass electrode. These results represent important progress in the fabrication of flexible transparent electrodes for future optoelectronics applications

One-Step Synthesis of Monodisperse In-Doped ZnO Nanocrystals

A method for the synthesis of high quality indium-doped zinc oxide (In-doped ZnO) nanocrystals was developed using a one-step ester elimination reaction based on alcoholysis of metal carboxylate salts. The resulting nearly monodisperse nanocrystals are well-crystallized with typically crystal structure identical to that of wurtzite type of ZnO. Structural, optical, and elemental analyses on the products indicate the incorporation of indium into the host ZnO lattices. The individual nanocrystals with cubic structures were observed in the 5% In–ZnO reaction, due to the relatively high reactivity of indium precursors. Our study would provide further insights for the growth of doped oxide nanocrystals, and deepen the understanding of doping process in colloidal nanocrystal syntheses