Rodrigo Martins

The effects of zinc concentration on the performance of solution processed amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) have been investigated using high-k aluminum titanium oxide as gate dielectric. The x-ray diffraction results confirmed that all the IGZO channel layers are amorphous. The performance of a-IGZO TFTs were investigated in the linear regime operation. Highest linear field-effect mobility of 5.8 cm2 /V s with an Ion / Ioff ratio of 6× 107 and subthreshold swing of 0.28 V/dec were obtained for the a-IGZO (311) TFTs. The obtained performance of the a-IGZO TFTs is very promising for low-voltage display applications. © 2010 American Institute of Physics.

This paper discusses the effect of order and disorder on the electrical and optical performance of ionic oxide semiconductors based on zinc oxide. These materials are used as active thin films in electronic devices such as pn heterojunction solar cells and thin-film transistors. Considering the expected conduction mechanism in ordered and disordered semiconductors the role of the spherical symmetry of the s electron conduction bands will be analyzed and compared to covalent semiconductors. The obtained results show p-type c-Si/a-IZO/poly-ZGO solar cells exhibiting efficiencies above 14% in device areas of about 2.34 cm2. Amorphous oxide TFTs based on the Ga-Zn-Sn-0 system demonstrate superior performance than the polycrystalline TFTs based on ZnO, translated by ION/IOFF ratio exceeding 107, turn-on voltage below 1-2 V and saturation mobility above 25 cm2/Vs. Apart from that, preliminary data on p-type oxide TFT based on the Zn-Cu-O system will also be presented. © 2009 SPIE.

A study of intrinsic zinc oxide thin film as ozone sensor based on the ultraviolet (UV) photoreduction and subsequent ozone re oxidation of zinc oxide as a fully reversible process was presented. It was found that the film described were produced by spray pyrolysis, dc and rf magnetron sputtering. The dc resistivity of the films changed more than eight orders of magnitude when exposed to an UV dose of 4 mW/cm2. Analysis shows that the porous and textured zinc oxide films produced by spray pyrolysis at low substrate exhibit an excellent ac impedance response.

Aluminium doped zinc oxide thin films (ZnO:Al) have been deposited on polyester (Mylar type D, 100 μm thickness) substrates at room temperature by r.f. magnetron sputtering. The structural, morphological, optical and electrical properties of the deposited films have been studied. The samples are polycrystalline with a hexagonal wurtzite structure and a strong crystallographic c-axis orientation (002) perpendicular to the substrate surface. The ZnO:Al thin films with 85% transmittance in the visible and infra-red region and a resistivity as low as 3.6×102 Ωcm have been obtained, as deposited. The obtained results are comparable to those ones obtained on glass substrates, opening a new field of low cost, light weight, small volume, flexible and unbreakable large area optoelectronic devices. © 2001 Materials Research Society.

In this paper we present results of intrinsic/non doped zinc oxide films deposited at room temperature by rf magnetron sputtering able to be used as a truly semiconductor on electronic devices like ozone gas sensors and ultra-violet detectors. The produced films are polycrystalline with a c-axis preferential orientation parallel to the substrate. The films' resistivity varies from 4.0×10-2 Ωcm to 1.0×10-9 Ωcm, depending on the deposition conditions used (rf power density and oxygen partial pressure), which turns not affecting the optical properties (in average a transmittance of around 85 % and an optical band gap of about 3.44 eV, independent of the deposition conditions used). When exposed to UV light the sensor response based on these films may exceed more than 5 orders of magnitude, recovering to the initial state in the presence of ozone. The sensitivity of the films is improved when the oxygen partial pressure increases and the rf power density used decreases, due to changes on the structural properties of the films. © 2006 Materials Research Society.

Zinc oxide (ZnO) has attracted recent interest for a range of applications, including use as a transparent conductive oxide (TCO) and in gas sensor devices. This paper compares ZnO films grown using two methods designed for the production of thin films, namely sol-gel and aerosol assisted chemical vapour deposition (AACVD) for potential use in sensor and TCO applications. Materials produced by the sol-gel route were observed to be amorphous when annealed at 350 °C, but were crystalline when annealed at higher temperatures and had a relatively open grain structure when compared to the AACVD films. Electrical characterization showed that materials were highly resistive, but that their properties varied considerably when the measurements were performed in vacuum or in air. This behaviour was rapidly reversible and reproducible for room temperature measurement. In contrast materials grown by aerosol-assisted CVD were non-porous, polycrystalline and conductive. Measured electrical properties did not vary with changing measurement atmosphere. These differences are discussed in terms of the structural characterisation of the films and some comments are made regarding the suitability of both approaches for the growth of ZnO thin film sensor materials. © 2009 Elsevier B.V. All rights reserved.

In this paper we report on some of the recent advances in transparent thin film oxide semiconductors, specifically zinc oxide produced by radio frequency magnetron sputtering at room temperature, with multifunctional properties. By controlling the deposition parameters it is possible to produce undoped material with electronic semiconductor properties, or by doping it to get either n-type or p-type semiconductor behavior. In this work we refer to our experience in producing n-type doped zinc oxide as transparent electrode to be used in optoelectronic applications such as solar cells and position sensitive detectors, while the undoped zinc oxide can be used as active layer of fully transparent thin film transistors. © 2009 Springer-Verlag.

Ga-doped polycrystalline zinc oxide (GZO) thin films have been deposited at high growth rates by rf magnetron sputtering. The dependence of electrical, optical and morphological properties on the rf power density were investigated. The lowest resistivity of 1.9×10-4 Ωcm was obtained for a rf power density of 9 W/cm2 and an argon sputtering pressure of 0.15 Pa at room temperature. The films are polycrystalline with a hexagonal structure and a strong crystallographic c-axis orientation (002) perpendicular to the substrate surface. The films present an overall transmittance in the visible spectra of about 85%. The low resistivity, accomplished with a high growth rate deposited at room temperature, enables the deposition of these films onto polymeric substrates for flexible optoelectronic devices and displays.