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Highly c-axis oriented ZnO thin films have been deposited on silicon substrates by planar rf magnetron sputtering under varying pressure (10-50 mTorr) and oxygen percentage (50-100%) in the reactive gas (Ar þ O 2) mixture. The as-grown films were found to be stressed over a wide range from À1 Â 10 11 to À2 Â 10 8 dyne/cm 2 that in turn depends strongly on the processing conditions, and the film becomes stress free at a unique combination of sputtering pressure and reactive gas composition. Raman spectroscopy and photoluminescence (PL) analyses identified the origin of stress as lattice distortion due to defects introduced in the ZnO thin film. FTIR study reveals that Zn-O bond becomes stronger with the increase in oxygen fraction in the reactive gas mixture. The lattice distortion or stress depends on the type of defects introduced during deposition. PL spectra show the formation of a shoulder in band emission with an increase in the processing pressure and are related to the presence of stress. The ratio of band emission to defect emission decreases with the increase in oxygen percentage from 50 to 100%. The studies show a correlation of stress with the structural, vibrational, and photoluminescence properties of the ZnO thin film. The systematic study of the stress will help in the fabrication of efficient devices based on ZnO film. V

Ultra-Voilet (UV) photodetector is fabricated by rf magnetron sputtered ZnO thin films of different thickness (50 to 400 nm). ZnO film with thickness 100nm is found to exhibit enhanced UV photo response in comparison to that observed in the thicker films and is thermally treated by two different techniques, one by furnace method and another by pulsed laser irradiation. In the furnace method, the as-grown 100nm ZnO thin film is post annealed in a range of temperature from 100°C to 400°C for 1hr. The I on /I off ratio of furnace annealed ZnO film of thickness 100 nm at 300°C is found to be (7 x 10 3 ) with fast response time of 50 ms in comparison to other annelead films. In the second method, as-grown 100nm ZnO film is irradiated by pulsed Nd:YAG laser corresponding to both fundamental wavelength (1064 nm) and forth harmonics (266 nm) to modify its defects profiles. Laser (λ=266 nm) irradiated detector exhibits enhanced response (3.7 x 10 4 ) with fast response speed (30ms), showing its promising application for detection of low intensity UV photons.

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