Nucleation and growth control in pulsed laser epitaxy of oxide thin films

Abstract

Due to the non-steady state nature of film growth by laser MBE, as well as by the conventional pulsed laser deposition (PLD), we could find an advantage of the method for controlling the film growth. The independent optimization of nucleation and growth processes is possible by pulse sequence and laser energy density. Another critical factor for controlling the growth mode was revealed to exist in the surface state of the substrate as the stating point of film growth. We have developed a wet etching method for automatically finishing SrTiO<SUB>3</SUB> substrate surface to facilitate the layer by layer growth of high Tc and other oxide thin films. The sequential deposition of SrO and BaO monolayers on the treated SrTiO<SUB>3</SUB> substrate greatly reduced the nucleation of precipitates in the YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7</SUB> (YBCO) thin films. Thus, PLD growth of YBCO thin film could be controlled on an atomic scale. Temperature gradient deposition achieved the orientational control of YBCO thin films on (100) and (110) SrTiO<SUB>3</SUB> substrates. Laser MBE successfully produced high quality epitaxial oxide films by 2-dimensional layer by layer manner as well as by step-flow mode, as verified by the sharp RHEED intensity oscillation. This dimension control epitaxy enabled us to fabricate oxide superlattices and quantum wires. With the substrate treatment and buffer layer techniques, together with suitable choice of insulating layer material, we have verified the fabrication of superconducting-insulating-superconducting trilayer which is the prototype for tunneling junctions. A possibility of using (110) oriented YBCO thin films for Josephson THz laser is also discussed.