Abstract:
Plasma polymerized tetraethylorthosilicate (pPIEOS) thin films were deposited to
glass substrates at room temperature by a parallel plate capacitively coupled glow
discharge reactor, The PPTEOS thin films were characterized by elemental analysis
(EA), scanning electron microscopy (SEM), infrared (IR) spectroscopy, differential
thermal analysis (DTA)J thermogravimetric analysis (fGA), ultraviolet-visible(Uvvis)
spectroscopy and de electrical measurements,
The EA and IR spectroscopic analyses indicate that the chemical composition and
structure of PPTEOS are different from that of the tetraethylorthosilicale (TEOS)
monomer. The empirical formula of the PPTEOS film is found to be C.,."HL2"
(SiO,)ooo_The SEM investigation shows a smooth, uniform and pinhole free surface of
the PPTEOS film The DT AlTGA analyses show that the degradation in the structure
and evolution of gases may occur most probably due to dehydrogenation and oxidative
reactions in the thin films in the temperatures between 313 to 1183K . It is observed
that the PPTEOS films are thermally stable up to about 446K From the Uv-vis
absorption spectra, allowed direct transition (Eqd), allowed indirect transition (E",)
energy gaps, Tauc parameter, B and extinction coefficient, K were detennined. The
E.,dand E.,; are 3.00 and 1,28 eV respectively, The value ofB is 442 em']." (eV),1!2.
The current density-voltage(J-Y) measurements were perfonned on the PPTEOS thin
films of different thicknesses in a aluminium! PPTEOS laluminium configuration over
o to 15 Y and temperature range from 300 to 423 K The J-V characteristic of
PPTEOS follows a power law dependence, J w '1"-, with a linear behavior (n ",,1) at the
lower voltage region fullowed by a non ohmic dependence with an exponent about 2
at higher voltage region. These results emphasize that the conduction mechanism is
space charge limited (SeL) conduction, Measurements of current density as a function
of temperature at constant applied voltages yielded different activation energies 1'£,
For 2 Y(ohmic) the values obtained are 0,13:t 0.05 eY and 0.46:f: 0,07 eV in the low
and high temperature regions respectively, For 14 V(non ohmic) the values of 8E are
0.09 :t 0.03 eY and 0.43 :t 0, I° eY in the low and high temperature regions
respectively, The conduction in PPTEOS may be dominated by hopping of carners
between the localized states at low temperatures and thermally excited carriers from
energy levels within the band gap in the vicinity of high temperature.
