Shinzo Takata

Transparent conducting p-type NiO thin films prepared by magnetron sputtering

Abstract Transparent and conductive thin films consisting of p -type nickel oxide (NiO) semiconductors were prepared by r.f. magnetron sputtering. A resistivity of 1.4 × 10 −1 ohms cm and a hole concentration of 1.3 × 10 19 cm −3 were obtained for non-intentionally doped NiO films prepared at a substrate temperature of 200°C in a pure oxygen sputtering gas. An average transmittance of about 40% in the visible range was obtained for a 110 nm thick NiO film. A semitransparent thin film pin diode consisting of p -NiO/i-NiO/i-ZnO/ n -ZnO layer having a voltage-current rectification characteristic and an average transmittance above 20% in the visible range was fabricated on a glass substrate.

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...

Conduction mechanism of highly conductive and transparent zinc oxide thin films prepared by magnetron sputtering

Abstract This report describes the results of experimental and theoretical studies of the electrical properties of highly conductive and transparent ZnO thin films prepared by magnetron sputtering. The mobilities of undoped and Al-doped ZnO (AZO) films (carrier concentration 10 20 -10 21 cm -3 ), which are relatively independent of the crystal quality, are mainly dominated by ionized impurity scattering. The relationship between the carrier concentration and the mobility of AZO films can be interpreted by the Brooks-Herring theory when both the degeneracy and nonparabolicity of the conduction band are taken into account. The origin of carriers in AZO films is also discussed.

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.

Highly Transparent and Conductive Zn2In2O5 Thin Films Prepared by RF Magnetron Sputtering

A new transparent conducting Zn2In2O5 film is demonstrated. The film was prepared by rf magnetron sputtering using binary compound targets composed of In2O3 and ZnO (with a Zn content (Zn/(Zn+In)) of 5-45 at%). The electrical properties were relatively independent of the substrate temperatures between room temperature and 350° C. A resistivity of 3.9×10-4 Ω· cm and an average transmittance above 80% in the visible range were obtained for undoped Zn2In2O5 films with a thickness of about 400 nm. The spatial resistivity distribution on the substrate surface was minimal for Zn2In2O5 films. Optical measurements showed a band-gap energy of about 2.9 eV and a refractive index of about 2.4 for Zn2In2O5. It was found that the resistance of the undoped Zn2In2O5 films was more stable than that of undoped ZnO or In2O3 films in oxidizing environments at high temperatures.

Preparation of transparent and conductive In2O3–ZnO films by radio frequency magnetron sputtering

Highly transparent and conductive In2O3–ZnO films have been prepared by rf magnetron sputtering using targets composed of In2O3 and ZnO. Polycrystalline Zn2In2O5 films were deposited at a substrate temperature of 350 °C using targets with a Zn content [Zn/(Zn+In)] of about 10–60 at. %. A uniform spatial resistivity distribution on the substrate surface was obtained even in Zn2In2O5 films deposited at room temperature. A resistivity of 3.4×10−4 Ω cm was obtained in Sn‐doped Zn2In2O5 films deposited at 350 °C. A sheet resistance of 400 Ω/sq and an average transmittance above 90% in the visible range were obtained for an undoped Zn2In2O5 film with a thickness of about 20 nm. The etching rate of In2O3–ZnO films when using HCl as the etchant could be controlled by the Zn content in the films.

Physics of very thin ITO conducting films with high transparency prepared by DC magnetron sputtering

The preparation of very thin indium tin oxide (ITO) films with extremely high transparency and suitable resistivity, as well as resistivity stability for long term use, is described. In order to obtain these properties, amorphous suboxide films were first prepared and then annealed. Suboxide films with a thickness of 20 to 30 nm were prepared on PET film and glass substrates at a temperature of 60 °C using In2O3SnO2 targets with a SnO2 content of 0 to 10 wt% by DC magnetron sputtering in a pure argon gas atmosphere. The films were annealed at a temperature of 150 °C for 1 to 100 h in air. The resistivity of films on PET films was, depending on the SnO2 content, on the order of 10−3 ω cm. An average transmittance above 97% in the visible wavelength range and a resistivity of about 4 × 10−3 ω cm, as well as resistivity stability, were attained in ITO films with a SnO2 content of about 1 wt% prepared on PET films by the low-temperature process. It is thought that these properties result from crystallization which occurred during the annealing, duration up to about 25 h.