Correlation between target-substrate distance and oxygen pressure in pulsed laser deposition of complex oxide thin films

摘要

A physico-chemical model is developed to describe a typical pulsed laser deposition (PLD) process. The interaction of atoms in the plume, ejected from the target, with those of the background gas (e.g. oxygen) is specifically considered. The model gives a physical definition of the 'plume range', which depends on the particular PLD system, and calculates the range. One prediction is that when the target-to-substrate distance (D) is optimised with respect to the oxygen pressure (P), the plasma dynamics plays an important role in growing high-quality complex oxide thin films. Our model predicts a scaling law PD~3 = const from thermodynamic data and the experimental volumetric erosion rate of the metallic elements ejected from the target. The volumetric erosion rate was experimentally determined by atomic force microscopy, measuring the dimensions of the crater formed in the target after a number of shots. The model was applied to the growth of three ternary oxides, CdTeO_3, AlVO_4 and PbFe_(12)O_(19) thin films, and the scaling laws predicted by our model using 420, 400 and 700℃ as substrate temperatures, respectively, were PD~3 = (3.3086, 5.9827, 30.3) x 10~3 mTorr cm~3 respectively, for the CdTeO_3, AlVO_4 and PbFe_(12)O_(19) thin films. In order to grow the thin films, we used an energy density of laser beam of 2 J/cm~2, and fixed D = 4.0, 4.0 and 3.0 cm from our scaling law; the values of P were 51.7, 130.0 and 751.8 mTorr, respectively. X-ray diffraction shows that the films are polycrys-talline and the observed peaks in the samples were similar with respect at its JCPDF patterns respectively.