Hidehito Nanto

Highly Conductive and Transparent Aluminum Doped Zinc Oxide Thin Films Prepared by RF Magnetron Sputtering

Highly conductive films of Al-doped ZnO have been prepared by rf magnetron sputtering of a ZnO target with Al2O3 dopant of 1–2 wt% in content added. Films with resistivity as low as 2×10-4 Ωcm and transmittance above 80% at the wavelength between 400 and 800 nm can be produced on low temperature substrate with a relatively high deposition rate. It is shown that a stable resistivity for use in various ambients at high temperature can be attained for the films. The characteristic features of Al-doped ZnO films are their high carrier concentration and low mobility in comparison with non-doped ZnO films.

Group III impurity doped zinc oxide thin films prepared by RF magnetron sputtering

The detailed study of electrical properties in group III impurity doped ZnO thin films prepared by rf magnetron sputtering is described. The resistivity is lowered by doping of B, Al, Ga and In into ZnO films. The characteristic features of ZnO films doped with group III elements except for B are their high carrier concentration and low mobility. Variation of the mobility with the impurity content is roughly governed by the ionized impurity scattering. It is shown that the doped ZnO films exhibit the resistivity dependence on film thickness below 300 nm.

Zinc‐oxide thin‐film ammonia gas sensors with high sensitivity and excellent selectivity

A sensor with a high sensitivity and an excellent selectivity for ammonia gas was prepared by using sputtered ZnO thin films. The sensor exhibited an increase of resistance for exposure to ammonia gas whereas it exhibited a decrease of resistance for exposure to many other gases such as inflammable and organic gases. The resistance change and the selectivity of the sensor were enhanced by doping group III metal impurities such as Al, In, and Ga. The lower limit of the detection for ammonia gas was about 1 ppm at a working temperature of 350 °C.

Electrical and optical properties of zinc oxide thin films prepared by rf magnetron sputtering for transparent electrode applications

Zinc oxide films were prepared on unheated glass substrates by rf magnetron sputtering under an applied external dc magnetic field in pure argon gas, and electrical and optical properties of the deposited films were investigated. Highly transparent films with resistivity as low as 10−4 Ω cm, which were weakly oriented perpendicular to the substrate surface(c‐axis orientation), could be produced with a relatively high deposition rate on the substrate suspended perpendicular to the target surface by controlling the sputtering gas pressure and the external dc magnetic field, without any postdeposition preparative treatment. The Hall mobility of the film with the highest conductivity was about 120 cm2/V sec, which was the highest yet reported for thin films on ZnO. The increase in the conductivity was related to the increase in Hall mobility which was caused by the decrease of carrier scattering from grain boundaries due to the grain growth resulting from the improvement of crystallization. The improvement of...

Highly conductive and transparent zinc oxide films prepared by rf magnetron sputtering under an applied external magnetic field

Highly conductive films of zinc oxide have been prepared by rf magnetron sputtering deposition on a substrate suspended perpendicular to the target under an applied external magnetic field in pure argon gas. It is shown that a film with low resistivity (5×10−4 Ω cm) and high optical transmission (>85% between 400 and 800 nm) can be produced on low‐temperature substrates with a relatively high deposition rate. The sheet resistance and Hall mobility of the film are 10 Ω/⧠ and 120 cm2/Vs respectively. The high conductivity is achieved by an increase in Hall mobility due to improved crystallization.

The stability of zinc oxide transparent electrodes fabricated by R.F. magnetron sputtering

Abstract The stability of the electrical, optical and mechanical properties of sputtered zinc oxide (ZnO) thin films with resistivities from 10−2 to 10−4 ωcm were investigated. No significant changes in these properties are observed for ZnO films exposed to air at room temperature for 10 months. A change in the electrical resistance of the ZnO films with temperature up to 400 °C is observed in various ambients such as vacuum, inert gases and air. After heat treatment in these ambients at 400 °C, the resistivity of the films increased by one to ten orders of magnitude. The increased resistivity can be returned to the resistivity of the virgin state, within one order of magnitude, by heat treatment in a hydrogen ambient at temperatures near 400 °C. For practical use of ZnO films at high temperatures, the increase in the resistivity might become a disadvantage for ZnO transparent electrodes fabricated by r.f. magnetron sputtering.

Optical Properties of Aluminum Doped Zinc Oxide Thin Films Prepared by RF Magnetron Sputtering

The detailed study of optical transmittance and reflectance in Al-doped ZnO thin films prepared by rf magnetron sputtering is described. Films obtained with Al2O3 content up to 10 wt% showed an average transmittance above 85% in the visible range. The absorption edge was blue-shifted with increasing carrier concentration. The shift was interpreted to be a result of competition between many body effects and the Burstein-Moss effect. It is shown that films obtained with an Al2O3 content of 1–2 wt% can achieve an excellent IR shielding.

Highly Conductive and Transparent Silicon Doped Zinc Oxide Thin Films Prepared by RF Magnetron Sputtering

Highly conductive and transparent films of Si-doped ZnO have been prepared by rf magnetron sputtering of a ZnO target with SiO2 or SiO dopant added. Films with resistivity as low as 3.8×10-4 Ω cm and average transmittance above 85% in the visible region can be produced on low temperture substrates at below 250°C. Great improvement in the stability of the resistivity for use at high temperatures was obtained for Si-doped ZnO films in comparison with undoped films.

Highly conductive and transparent ZnO thin films prepared by r.f. magnetron sputtering in an applied external d.c. magnetic field

Highly conductive films of undoped and aluminum-doped ZnO were prepared by r.f. magnetron sputtering in an applied external magnetic field in pure argon gas. Films with a resistivity as low as 2 × 10-4 Ω cm and a transmittance above 80% at wavelengths between 400 and 800 nm can be produced on a non-intentionally heated substrate by the sputtering of a ZnO target to which 2 wt.% Al2O3 had been added. The characteristic features of aluminum-doped ZnO films are their high carrier concentration, low mobility and blue shift in the absorption edge in comparison with the properties of undoped ZnO films.

The stability of aluminium-doped ZnO transparent electrodes fabricated by sputtering

Abstract The stability of the electrical, optical and mechanical properties of sputtered aluminium-doped ZnO (AZO) films with a resistivity from 10 -3 to 10 -4 Ω cm was investigated. No significant change in these properties of AZO films was observed for use in air at room temperature for 1 year. It is shown that stable properties for use in vacuum and inert and nitrogen gases at temperatures as high as 400°C can be attained for AZO films sputtered with an Al 2 O 3 content above 1.0 wt.%. After heat treatment in air at 400°C, the resistivity of AZO films increases by about five orders of magnitude. The resistivity can be returned to that of the as-deposited state by heat treatment in hydrogen gas at a temperature near 400°C.