Surface-controlled growth of LaAlO3 thin films by atomic layer epitaxy

Abstract

LaAlO3 thin films were deposited by atomic layer epitaxy (ALE) from β-diketonate-type precursors La(thd)3 and Al(acac)3. Ozone was used as an oxygen source. Films were grown on soda lime glass, Si(100), MgO-buffered Si(100), sapphire and SrTiO3(100) substrates. The influence of the La∶Al precursor pulsing ratio on the film growth and quality in the temperature range of 325–400 °C was studied in detail. Stoichiometry and impurity levels were measured using RBS, TOF-ERDA and XPS while the chemical type of carbon impurity was identified by FTIR. XRD and AFM were used to determine crystallinity and surface morphology. The films were transparent and uniform and their thickness could be accurately controlled by the number of deposition cycles. The as-deposited films were amorphous but became crystalline upon annealing at 900 °C. The annealed films grown on Si(100) and MgO(111)-buffered Si(100) substrates had a preferred (110) orientation whereas those grown on MgO(100)-buffered Si(100) substrates showed a preferred (100) orientation. Epitaxial and smooth LaAlO3 thin films were obtained on SrTiO3(100) after annealing at 900 °C, verified by measurement of the X-ray rocking curve of the (200) reflection and the AFM surface roughness. Stoichiometric LaAlO3 films contained <1.9 atom% carbon and about 0.3 atom% hydrogen as impurities.