GROWTH OF HIGHLY TRANSPARENT OXIDE LAYERS BY PULSED-LASER DEPOSITION - REDUCTION OF DROPLET DENSITY

Thin layers of ZnO and CeO2 have been grown on Coming glass and Si sub strates by pulsed laser deposition (PLD) method. Under optimised condi tions, films exhibiting absorption coefficients in the visible region as low as 4 x 10(2) cm and 3 x 10(3) cm(-1) for ZnO and CeO2, respecti vely, have been deposited at a substrate temperature of only 350 degre es C. When using the PLD technique, the grown layers very often exhibi t some micrometer sized droplets. Although the surface density of thes e can be dramatically reduced, there is still much effort being direct ed at completely eliminating their presence, which could clearly restr ict the applications. There is still much controversy concerning the m echanisms of droplet formation, whether they are caused by a sub-surfa ce super-heating effect or by explosive boiling, Careful scanning elec tron microscopy investigations of various target surfaces after the la ser ablation process and numerical simulations of the temperature dist ribution inside these tar ets during the action of the laser pulse ten d to support the sub-surface super-heating effect as a one of the main causes of droplet emission.