Ryōsuke Konishi

The preparation of transparent ZnO: Al thin films

Abstract Transparent conductive ZnO: Al films were prepared by the facing-target-type sputtering method. The films typically showed poor conductivity immediately after sputtering. However, at optimum conditions, they manifested their lowest resistivity of 4×10 -4 Ω cm after heat treatment at 400°C. The decrease in resistivity is mainly attributed to the improvement of the Hall mobility which in essence is not due to crystallinity improvement, but rather due to the decrease of excess oxygen atoms at the interstitial state or the grain boundaries. However, even without heat treatment we obtained a low resistivity of 5.3×10 -4 Ω cm under low oxidation sputtering condition at 0.1 Pa with oxygen to argon ration of 1:4.

Heat Treatment Effects of ZnO:Al Thin Films Prepared by Facing-Target-Type Sputtering Method

ZnO:Al films were deposited by a facing-target-type method on a glass substrate, which is held at 300°C. The minimum resistivity was obtained with an Al concentration of 1.3%. The decrease of resistivity after the heat treatment of ZnO:Al (1.3%; calculated from area ratio of target) film seems to be mainly attributed to the increase of Hall mobility. The improvement of Hall mobility is not due to the improvement of crystallinity, but it may be due to the decrease of oxygen impurities at interstitial sites.

Observation of sorption of O2 and N2 on Ti thin film by DAPS, AEAPS, AES and electrical resistance methods

The sorption process of Ti thin films during oxygen and nitrogen exposure has been investigated using a combination of DAPS, AEAPS, AES and electrical resistance measurements. In the case of oxygen exposure, oxygen atoms diffuse into layers up to 3–5 A beneath the surface at an exposure of 4L. Further exposure of 5–100L enhances the diffusion, probably to a depth of 6–10 A. Furthermore, comparison of DAPS and AEAPS measurements shows that a stable surface oxidation layer is formed in the 6–10 A layer at an exposure of 100L. In the case of nitrogen exposure, nitrogen atoms adsorb on the surface at 3–4L. After that, nitrogen atoms diffuse into the layer 6–10 A below the surface at exposure of 7–10L, followed by saturation. The saturation value of the diffusion depth of nitrogen atoms in Ti thin films is found to be much smaller than that of oxygen atoms.

The Adsorption Process of Hydrogen on Titanium Films, a CPD and QCM Study

We combined a contact potential difference (CPD) method and a quartz crystal microbalance (QCM) method to estimate quantiatively the sorption process of hydrogen atoms in titanium films. At the adsorption of less than about 1.2×1017 atoms/cm2, the exsistence of both r-type and s-type adsorption states was confirmed. At further adsorption, the changes of CPD and QCM suggest the formation of a stable hydride and the existence of s-type adsorption stable on hydride.

Characteristics of ZnO:Al Transparent Conductive Films

Conduction mechanism of sputtered ZnO:Al thin film was studied for developing heat resistant transparent electrodes of EL devices. Strong evidence of the formation of the Al donors in ZnO:Al films was obtained by XPS measurements. X-ray diffraction measurements showed that the decrease of the mobility with increasing Al concentration above 1.3% was partly due to the low crystallinity of the films.

Extended Appearance Potential Fine Structure Analysis of Chromium

The EAPFS (Extended Appearance Potential Fine Sructure) of chromium was observed. We obtained a nearest-neighbor atomic spacing of 2.53±0.1 A(l=0), 2.54±0.1 A(l=1) and 2.54±0.1 A(l=2), respectively, by correcting the phase shift which was dependent on the final state of angular momentum l. These values are in good agreement with that for bulk values (2.50 A).

Extended Appearance Potential Fine Structure Analysis of Zinc Oxide

We attempted to analyze the fine structure above Zn-M2,3 appearance potential spectra of transparent conductive (TCO) ZnO thin film. The analysis was done in two different cases. One in which the effect on the fine structure from the Zn-M1 edge is considered and the other is in which it is not. From the results of the analyses, it can be considered that there is no effect from the Zn-M1 edge. The nearest-neighbor atomic spacing of the TCO ZnO film is 0.202 nm. This value is in good agreement with that of SEELFS.

Adsorption of Oxygen SnOx Thin Film

The change in electrical resistance and the surface potential of SnOx thin film by the adsorption of oxygen were observed. At an oxygen pressure of 6.7×10-4 Pa, both changes result in a decrease. At further adsorption, the change in the electrical resistance ascends abruptly at about 10-2 Pa. These changes can be explained by devising a model of band bending.

Surface structure analysis of polycrystalline zinc by SEELFS and EAPFS

From the view point of comparing SEELFS with EAPFS, we tried to measure the fine structure above the Zn-M2,3 threshold of polycrystalline zinc. From the result of SEELFS, we were able to obtain a nearest-neighbour atomic spacing of 0.242 nm. In EAPFS, we obtained the nearest-neighbour atomic spacings of 0.241 (l=2), 0.251 (l=1) and 0.261 nm (l=0). The result of EAPFS agrees well with that of SEELFS when we assume a final state of l=2, in spite of a lack of dipole selection rules.

The Analysis of Surface Extended Energy Loss Fine Structure of Zinc Oxide

The SEELFS (Surface Extended Energy Loss Fine Structure) of zinc oxide was observed. We obtained a nearest-neighbor atomic spacing of 0.202±0.001 nm (l=2) by correcting the phase shift which was dependent on the final angular momentum of l. This value is about 0.007 nm longer than the one of bulk.