Growth of PbS thin films from novel precursors by atomic layer epitaxy

Abstract

Two lead tert-butoxide complexes (1)[Pb(Obu^t)₂]_m(m= 3 or 2 in the solid and gaseous phase, respectively) and (2) Pb₄O(OBu^t)₆ were used as precursors for atomic layer epitaxy (ALE) deposition of PbS thin films. The growth on soda lime glass, with and without an alumina coating, was studied by varying the source furnace and the substrate temperatures as well as the total number of cycles. Pb(thd)₂(3) and Pb(dedtc)₂(4) were used for comparison while H₂S served in all experiments as the sulfur source. The films obtained were smooth and generally highly crystalline. The substrate temperature had a strong effect on the growth rate of PbS thin films. Nevertheless, in the self-controlled region of ALE growth the tert-butoxide complexes gave a significantly higher growth rate than the other source chemicals, with a maximum of 0.9 Å per cycle at 150 °C. Upon sublimation 1 is converted to 2, which contains four Pb atoms in a tetrahedral arrangement; this may cause the higher growth rate. Thermogravimetry/differential thermal analysis curves and mass spectrometric data were measured for all precursors. As the butoxide and thd complexes (1–3) are thermally unstable the useful ALE prosessing windows (temperature/pressure) are narrow compared to the much more stable dedtc complex (4).