Papers by Author: Yutaka Adachi

Abstract: The a-axis oriented ZnO thin films deposited on sapphire substrates by pulsed laser deposition were studied to investigate the effects of pre-annealing on oxygen diffusion. The effect was as follows: the oxygen diffusion coefficient decreased, and the oxygen concentration in the tailing regions of the profiles reduced. Ion images of an oxygen tracer revealed the high-diffusivity paths for oxygen tracer diffusion. The temperature dependence of oxygen tracer diffusion coefficients (D_b) in as-deposited and pre-annealed thin films were determined to be D_b [cm²/ = 9.2x10² exp (- 405 [kJ/mo / RT) and D_b [cm²/ = 1.8x10³ exp (- 418 [kJ/mo / RT), respectively. On basis of these results, the crystal orientation on D_b and the mechanism for oxygen diffusion were discussed.

Abstract: The processes for polishing a ZnO surface were investigated with the aim of establishing a process for obtaining an atomically flat surface with high crystalline quality. The defects in a layer undergoing mechanical polishing were monitored through photoluminescence measurements, and the purity of the polished surface was characterized by SIMS. An atomicallyfishing process.

Abstract: The resistivity of transparent conductive thin film formed by sputtering exhibits a dependence on film thickness. In this study, an analysis by electromagnetic field simulation of resistance effect on the transmission characteristics was carried out. The overall resistance of the signal waveguide governs the transmission characteristics, and variation of the resistance at the interface between the substrate and the thin film has no significant effect. We evaluated a structure in which fine metal wiring that is not visible to the eye is placed on transparent conductors to reduce the resistance of the transmitting waveguide. Electromagnetic field simulations suggest that this structure improves the transmission characteristics while keeping high transparency.

Abstract: The relationship between Al and Li during diffusion was studied using Al-implanted ZnO. The Al donor in ZnO acts to increase the concentration of Li contamination from the atmosphere during the annealing. It is difficult to decompose the relationship formed by diffusion between Al and Li during high-temperature annealing. The most effective method to decompose the relationship is to anneal the as-implanted ZnO at a pressure of 5×10-3 torr. This annealing increases the Al solubility limit because the ZnO surface evaporates.

Abstract: The relationship between the defect structure and luminescence property of ZnO ceramics implanted with Ar of 2×1015 – 60×1015 ions/cm2 was studied. After annealing, the heavy dose-implanted sample (Ar ≥ 30×1015 ions/cm2) was characterized by a luminescence peak at the 730-nm wavelength. Defects in the implanted region formed voids during post-annealing. Oxygen tracer experiments indicated that grain boundary diffusion in the implanted region was enhanced significantly.

Abstract: Zinc isotopic heterostructured zinc oxide thin films of 64ZnO/68ZnO/64ZnO were synthesized using pulsed laser deposition. The pulsed laser was first irradiated onto a polycrystalline target of 64ZnO to deposit the 64ZnO layer, then onto the 68ZnO target to prepare the 68ZnO layer and finally, the 64ZnO target was used again. The 64ZnO/68ZnO/64ZnO layered thin film was thus obtained. The thin films were annealed at various diffusion annealing temperatures. Diffusion profiles of the zinc isotopes due to the annealing were evaluated using secondary ion mass spectrometry (SIMS). The diffusion coefficients were slightly higher near the interface between the thin film and the substrate (the inner region) compared to the near surface (the outer region).

Abstract: The effect of ion implantation leading to contamination and diffusion of lithium impurity in ZnO ceramics substrates was investigated. The diffusion coefficients of Li in the implanted ZnO annealed at 1000 and 850°C were in good agreement with those in the non-implanted ZnO. At 700°C, Li diffusion in the implanted ZnO was strongly enhanced. Our results show that the defects introduced by the implantation enhance the impurity diffusion at low temperature annealing.

Abstract: (Mg,Zn)O films were grown on Zn- and O-face ZnO single crystal substrates by pulsed laser deposition. The surface morphologies of the films grown on the Zn- and O-face substrates were quite different, indicating that no domain inversion occurred in both films. The films showed markedly different features for valence band spectra obtained by hard X-ray photoemission spectroscopy. This suggests that the effect of film polarity should be considered in X-ray photoemission spectroscopy.

Abstract: The defect structure of undoped ZnO and (Zn1-x,Mgx)O solid-solution films were deposited on YSZ substrate with pulsed laser deposition (PLD) to investigate defect equilibria in those films. In particular, the effects of thermal treatment on the structures and prosperities of (Zn1-x,Mgx)O
solid-solution films were examined. The films with high MgO concentration (x>0.12) decomposed to the wurtzite-type and rock-salt-type phase after thermal treatment, indicating that the solubility limit of Mg was about x=0.12 and the wurtzite-type (Zn,Mg)O films with x>0.12 were indicated to be non-equilibrium ones. The subsequent analyses of oxygen diffusivity in those films revealed that the films under non-equilibrium state, i.e., wurtzite-type (Zn1-x,Mgx)O with x>0.12, contained significantly high concentration of anion defects.