Kenkichiro Kobayashi

Presumption and improvement for gallium oxide thin film of high temperature oxygen sensors

In this paper the gallium oxide thin film oxygen gas sensor operated at the high temperature over 900 °C has been analyzed. Gallium oxide thin films have been deposited by sputtering method using a powder target instead of a ceramic target. The sensing characteristics, sensitivity and response time of the sensor has been studied. Crystallinity and composition of the produced films have been evaluated by XRD and AES. The sensing characteristics of the sensor for oxygen gas response were measured at 1000 °C. The results of the film obtained from a powder target show lower in resistance, higher in sensitivity and faster in gas response rate in comparison with those obtained from a ceramic target. AFM measurements have been done to observe the surface of thin film. It has been found that there are differences in size of grain due to different sputtering conditions and targets. It is also shown that oxygen gas response, depend on the grain size and surface structure of the materials. A very fast and normal rate rising time has been estimate by the combination of a surface contact model and bulk contact model. The simulation results are compared with the experimental measured data. A good qualitative agreement is found with them.

Doping of Bonds into ZnO Films and the Changes of their Electric Properties

ZnO films codoped with Mg and N atoms have been prepared by sputtering of a target of a mixture of ZnO and Mg3N2 powders. The c-axis lengths of ZnO films increase with the concentration of Mg3N2 in the target. After annealing in an atmosphere of 99% N2 and 1% O2, the ZnO film prepared by sputtering of 20 at.% Mg3N2 target at 70 W in an N2 atmosphere becomes a p-type semiconductor with the resistivity of 400 Ωcm although the ZnO films prepared at 20 and 120 W in an N2 atmosphere become insulators. INTRODUCTION Zinc Oxide (ZnO) has attracted a great deal of attention from ultraviolet laser diodes. The p-n junction is necessary for the fabrication of such laser diodes. An n-type ZnO has been obtained by doping Group III elements. Although the preparation of p-type ZnO has been attempted by doping of N atoms, no one succeeded in the growth of p-type ZnO. In recent, several groups reported that hole-conductivity was found in ZnO containing excess Zn-N bonds or Ga-N bonds [1,2], but there were serious problems on reproducibility. In addition to the low solubility of N atoms, there is a possibility that the energy levels of N-related acceptors are not shallow [3]. According to the codoping theory [4], the N-related levels could be lowered by the incorporation of Be-N or Mg-N bonds into ZnO. In previous papers [5,6], we reported that hole conductivity was achieved in ZnO films containing Be and N atoms. Although Be-N bonds in ZnO are expected to act as effective acceptors, it is not preferable to use such toxic Be compounds. In the present work, we attempt to prepare p-type ZnO films by doping Mg-N bonds. ZnO films codoped with N and Mg atoms are prepared by sputtering of a target of a mixture of ZnO and Mg3N2 powders. The characterization of sputtered films is carried out by X-ray diffraction (XRD) and X-ray photoelectron spectroscopic (XPS) measurements. The effects of codoping of Mg and N atoms on both the electric resistivity and carrier types are discussed. EXPERIMENTAL ZnO films containing Mg and N atoms were prepared by a radio frequency (RF) magnetron sputtering technique. A target was a mixture of ZnO (99.999%) and Mg3N2 powders. The concentration of Mg3N2 in the target was changed from 0 to 40 at.%. ZnO films containing Mg Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vol. 269, pp 79-82 doi:10.4028/www.scientific.net/KEM.269.79

Doping of Nitrides into Zinc Oxide Films

ZnO films containing Be and N atoms have been prepared by simultane ous sputtering of ZnO and Be in a N2 atmosphere. The c-axis length of ZnO film is shortened with an increase of dc power of the Be sputtering, indicating the incorporation of Be atoms in Z nO. The hole conductivity is found in ZnO film containing both 18% Be and 1.2% N atoms.