Transparent conductive oxide (TCO) films have been extensively used in optoelectronic devices because of their high visible transmittance and low dc resistivity. Recent investigations point out that ZnO, which combines semiconducting behavior with optical transparency in the visible range, will be one of the most competitive semiconductors in the near future.

Pure ZnO and Al-doped films about 100 nm thick were prepared onto Cz-Si (1000) type p (carrier concentration 10²⁰ cm^-3) substrates by spray pyrolysis. The deposition parameters were chosen to ensure a good optical transparency. The structure and chemical analysis confirmed the formation of Al-doped and undoped ZnO and the absence of other phases or compounds. More details about preparation and characterization of undoped and Al-doped ZnO films have been published elsewhere.

PES spectra were recorded using synchrotron radiation at VUV PHOTOEMISSION Beamline of the ELETTRA synchrotron (Trieste). The interfaces were studied using VB, Al 2p and Si 2p (bulk binding energies 72.5 and 99.2 eV) spectra. Ar⁺ ion beam sputtering was used to reduce the pyrolysis layer thickness progressively, in order to reveal the ZnO:Al/Si or the ZnO/Si interface, where an intermediate SiO_x oxide layer has been detected. In order to maintain the oxygen stoichiometry, ion beam sputtering was followed by light oxidation (20 Langmuirs 10^-6 Torr for 20 seconds). In spite of the weak signal coming from Al 2p state (nominal doping was 3%), the high photon flux at low energies in ELETTRA facility, has allowed to distinguish contributions due to two different chemical environments, octahedral and tetrahedral. Their respective intensities change with sputtering deep, which suggests Al segregation at the junction with SiO_x.

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1. SURFACE MORPHOLOGY OF ZnO/ZnS bilayer obtained by Chemical Spray Pyrolysis
2. Electronic structure of sputtering deposited undoped and Ga-doped ZnO thin films on a commercial Cz-Si solar cell substrate.
3. Iron oxide and oxyhydroxides thin films obtained by electrodeposition
4. Hetereojunction
5. THE CONDUCTION MECHANISM OF Al-DOPED ZnO, AZO, FILMS