Metal chalcogenide thin films have
a wide variety of applications
and potential uses. Tin(II) sulfide is one such material which presents
a significant challenge with the need for high quality SnS, free of
oxide materials (e.g., SnO2) and higher tin sulfides (e.g.,
Sn2S3 and SnS2). This problem is
compounded further when the target material exhibits a number of polymorphic
forms with different optoelectronic properties. Unlike conventional
chemical vapor deposition (CVD) and atomic layer deposition (ALD),
which rely heavily on having precursors that are volatile, stable,
and reactive, the use of aerosol assisted CVD (AA-CVD) negates the
need for volatile precursors. We report here, for the first time,
the novel and structurally characterized single source precursor (1), (dimethylamido)(N-phenyl-N′,N′-dimethylthiouriate)tin(II) dimer,
and its application in the deposition, by AA-CVD, of phase-pure films
of SnS. A mechanism for the oxidatively controlled formation of SnS
from precursor 1 is also reported. Significantly, thermal
control of the deposition process allows for the unprecedented selective
and exclusive formation of either orthorhombic-SnS (α-SnS) or
zinc blende-SnS (ZB-SnS) polymorphs. Thin films of α-SnS or
ZB-SnS have been deposited onto Mo, fluorine doped tin oxide (FTO),
Si, and glass substrates at the optimized deposition temperatures
of 375 and 300 °C, respectively. The densely packed polycrystalline
thin films have been characterized by X-ray diffraction, scanning
electron microscopy, atomic force microscopy, Raman spectroscopy,
energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy
analysis. These data confirmed the phase purity of the SnS formed.
Optical analysis of the α-SnS and ZB-SnS films shows distinctly
different optical properties with direct band gaps of 1.34 and 1.78
eV, respectively. Furthermore, photoelectrochemical and external quantum
efficiency (EQE) measurements were undertaken to assess the optoelectronic
properties of the deposited samples. We also report for the first
time the ambipolar properties of the ZB-SnS phase.
