Yttrium oxide and barium strontium titanate (BST) thin films were grown directly on Si substrates by the pulsed laser deposition (PLD) technique. Because the optimum oxygen pressure during PLD process is of the order of 10 mTorr, some of the oxygen atoms are trapped inside the grown films and contribute to the growth of a silicon oxide interfacial layer. The use of an UV source during the growth resulted in the reduction of the optimum oxygen pressure and, as a consequence, the amount of trapped oxygen and thickness of the interfacial layer. In addition to that, UV radiation influenced the film morphologies and electrical properties. A further reduction of the interfacial layer was obtained on substrates that were exposed prior to deposition to NH3 for short periods of time under UV radiation.