Tin Monosulfide Thin Films Grown by Atomic Layer Deposition Using Tin 2,4-Pentanedionate and Hydrogen Sulfide

Tin monosulfide (SnS) was grown by atomic layer deposition (ALD) using sequential exposures of tin(II) 2,4-pentanedionate (Sn(acac)(2)) and hydrogen sulfide (H2S). In situ quartz crystal microbalance (QCM) studies showed that the SnS ALD mass gain per cycle was 11-12 ng/cm(2) at 175 degrees C on a gold-covered QCM sensor. Using a film density of 5.07 g/cm(3) determined by X-ray reflectivity measurements. these mass gains are equivalent to SnS ALD growth rates of 0.22-0.24 angstrom/cycle. The ratio of the mass loss;did mass gain (vertical bar Delta m(2)/Delta m(1)vertical bar) from the H2S and Sn(acac)(2), reactions was vertical bar Delta m(2)/Delta m(1)vertical bar similar to 0.32 at 175 degrees C. This measured ratio is close to the predicted ratio from the proposed surface chemistry for SnS ALD. The SnS ALD was sell-limiting versus the Sn(acac)(2), and H2S exposures. The SnS ALD growth rate was also independent of substrate temperature from 125 to 225 degrees C. The SnS ALD growth on Al2O3 ALD substrates displayed nucleation problems and smaller growth rates. These differences may be caused by site blocking by the Al(acac)* surface species. X-ray fluorescence studies confirmed a Sn/S atomic ratio of similar to 1.0 for the SnS All) films. X-ray photoelectron spectroscopy measurements revealed that the SnS ALD films contained oxygen impurities at 15-20 atom % after air exposure. These oxygen-containing. SnS ALD films displayed a band gap of similar to 1.87 cV that is higher than the SnS bulk value of similar to 1.3 eV. In addition, these SS ALD films produced very weak photoluminescence at room temperature. SnS ALD may be useful to fabricate photovoltaic or solar conversion devices.