Photoluminescence studies of pulsed laser deposited films

Summary form only given. A detailed study of pulsed laser deposited ZnO and Si thin films for its applications as a medium of UV laser is presented. The films were deposited using pulsed laser deposition technique using third harmonic of 355 nm and fundamental wavelength of a Q- switched Nd:YAG laser. Substrate (glass, Si, sapphire) was kept at a distance of 4 cm from the target. The structural characteristics of as deposited films were studied prior to looking for laser action in them. The average diameter of nanocrystallites is estimated using the broadening of the diffraction peaks in the Scherrer´s formula. The size of nanocrystallites varied from 7 to 16 nm (with an error of less than 20 %). The substrate temperature, ambient gas pressure and target substrate distance, in addition to laser parameters are the factors that control the width of the diffraction peaks and hence the size of the nanocrystallites. Surface morphology of the films was studied using AFM. Surface morphology varied among films grown at various ambient pressures. The average roughness varied from 20 to 108 nm within the scanned area of 1/spl times/1 gm/sup 2/ in the pressure range studied. The root mean square (RMS) value of the grain size ranged from 20 to 200 nm. Photoluminescence study was done by exciting the ZnO thin films using third harmonic (355 nm, pulse width 5 ns) and second harmonic (532 nm, pulse width 6 ns) of the Nd:YAG laser. Emission spectra from the samples were recorded using a fiber coupled to the Monochromator (Jobin Yvon, HRS 2). To observe laser action the sample were optically pumped with the third harmonic (355 nm, pulse width 5 ns) of a Q-switched Nd:YAG laser. A steep rise in the output after the input pump energy exceeds a critical value has been observed which can be taken as the lasing threshold. Below the threshold excitation intensity, the spectrum observed is a single broad spontaneous emission peak. As the input intensity increases, the emission becomes na- rower due to preferential amplification at frequencies close to the maximum of the gain spectrum. The intensity of the laser emission increased with the increase of film thickness. The increased emission is attributed to a longer optical path in thick films contributing to amplification. An extensive investigation of the nonlinear optical properties of ZnO thin films deposited under different ambient pressures of oxygen was undertaken. The dependence second harmonic coefficient (X/sub eff//sup (2)/) for different films deposited under different ambient conditions will also be reported.