Undoped and Ga-doped (3 wt %) n-type ZnO thin films were grown by a reactive plasma deposition method on glass substrates at 200 °C under an oxygen flow rate from 0 to 50 SCCM. In this paper, we report on the defect and band edge related signals in the optical absorption spectra for ZnO thin film by using a piezoelectric photothermal (PPT) spectroscopy, which is effective in observing a nonradiative transition process. The PPT peak around 2.5 eV was observed only for the undoped ZnO samples grown under a low oxygen flow rate. This signal is considered to be related to the oxygen vacancies, because it disappears with the increase of the oxygen flow rates. No corresponding peak was found for the Ga-doped samples. This result indicates that Ga doping inhibits the generation of the oxygen vacancies, and it agrees with that from the first-principle electronic band structure calculations. We have also carried out the theoretical calculation for the optical absorption edge of degenerated ZnO as a function of the carrier concentration. Burstein-Moss effect and band-gap-narrowing effect in ZnO should be considered in the case of high carrier concentration. Comparing the experimental results with the theoretical predictions, we found out that the proposed PPT edge energy coincides well with the Fermi level EF.

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N-type ZnO thin films were successfully grown by sol-gel dipping coat method on glass substrates at 300 -600 °C under air atmosphere. Poly ZnO thin films were obtained at more than 300 °C. Values of full width at half maximum of (0002) peak at the XRD spectra became small with the increasing the substrate temperatures. Optical transmittances of the ZnO thin films increased with the increasing the substrate temperatures. The optical transmittance of Ga-doped ZnO thin films was larger than In-and Al-doped ZnO films (5 wt%). Moreover, a resistivity of Ga-doped ZnO was smaller than those of In-and Al-doped ZnO films. X-ray photoemission spectroscopy (XPS) results indicated that a chemical shift of oxygen (1s) in Ga-doped ZnO was smaller than those of In-and Al-doped ZnO films. These indicated that Ga atoms were easy to substitute of Zn atoms in comparison with In and Al atoms. This result was clear from the ionic radius and the covalent radius of Ga atoms, which were similar to those of Zn compared with Al and In atoms.Introduction Wide bandgap oxide-semiconductors have attracted much attention for liquid crystal displays and solar cells. A ZnO material is a semiconductor with a hexagonal structure and a large bandgap of 3.4 eV at room temperature. Recently, ZnO based materials are much respected for UV lightemitting devices. Optically pumped UV emission at RT has been already reported [1]. Group-III elements such as Al, Ga and In, and group-VII elements such as Cl, Br and I can be used as n-type dopants in the ZnO material [2 -4].In this work, n-type ZnO thin films were grown by sol-gel dipping coat method on glass substrates at 100 -600 °C under air atmosphere. The sol-gel technique is known to have the distinct advantages of process simplicity, low cost and easiness of composition control. Precursor solutions of n-type ZnO are prepared by dissolving both 95 wt% zinc acetate dihydrate and 5 wt% Al, In or Ga acetate dihydrate into anhydrous ethanol for the solutions to have the desired group-III/Zn wt%.Crystal structures of the ZnO thin films were examined by the X-ray diffraction (XRD) measurement. Optical and electrical properties of the ZnO films were also obtained by the optical transmittance and the four-probe point measurements, respectively. X-ray photoemission spectroscopy (XPS) was used to analyze the film composition and the chemical bonding of the elements.

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AgInS 2 crystal could be grown by a Hot-Press (HP) method with pressure (10 ~ 90 MPa) at 700 ˚C. From X-ray diffraction measurements, the samples grown at 10 ~ 40 MPa were found to contain only AgInS 2 phase. However, a signal from AgIn 5 S 8 phase increased with increasing pressure above 40 MPa. The lattice parameters of a and c axes increased and were almost constants with increasing pressure below and above 40 MPa, respectively. A donor-type defect of interstitial Ag might be enhanced to electrical conductivity in the all samples because samples indicated n-type conductivity examined by thermoprobe analysis. Moreover, high purity sample could be obtained in the HP method because a free exciton emission was clearly and no deep emission was observed in the photoluminescence spectrum.