Amorphous and crystalline silicon carbide are semiconductor materials with remarkable potential applications due to their outstanding
chemical and physical properties such as a wide tunable optical band gap, good chemical resistance, high hardness, high breakdown field, high saturated
drift velocity and high thermal conductivity and stability. From the exprimental poin of view, a number of techniques have been
used for the films preparation, the most commonly used being chemical vapor deposition(CVD), dynamic ion mixing, pulsed laser ablation and RF sputterng.
We studied the structural properties of Si1-xCx thin films deposited by pulsed laser ablation of a polycrystalline silicon
carbide target in vacuum. The influence of the deposition parameters on the optical and structural properties
of the samples was investigated by means of Fourier transform IR, Raman, ex situ ellipsometric, x-ray photoelectron, and x-ray absorption near edge structure spectroscopies.
XANES spectra of SiC thin → films deposited at different substrates temperature and laser fluences.
Both deposition temperature and laser fluence were increased up to 1150 K and 14 J /cm
2, respectively. Increasing the two parameters, a better quality of the thin films was observed due to the existence of a
crystalline order on a nanometric scale. Nevertheless, at higher deposition temperatures, a graphitic phase occurred inducing a degradation of the optical properties. Such a phase was not observed
increasing the laser fluence.
One of the major advantages offered by this kind of material is the possibility to tailor its optical, electrical,
and structural properties by varying, in an appropriate way, its stoichiometry. For example, the incorporation of hydrogen
atoms into the films can improve significantly their optical and electronic properties, while the introduction of fluorine
atoms improves the thermal stability of the films, resulting in both an optical band gap widening and a decrease
in the electrical conductivity values. Moreover, from a fundamental point of view silicon carbon alloys represent
an intriguing system where chemical disorder is added to that of the topological origin. In this respect the ternary
system SiC
xN
y has attracted, over the past few years, the interest of researchers, mainly because its properties could,
in principle, be tuned between those of silicon carbide, carbon nitride, and silicon nitride. In fact, taking into account
that
β-Si
3N
4 and
β-C
3N
4 , for which hardness comparable to that of diamond have been predicted, are isostructural
and hence completely miscible, SiCN alloys may present peculiar mechanical and electronic properties. Nevertheless,
this picture is rather complicated by the wide compositional range available and by the fact that, even for a given stoichiometry,
the properties of the films could be strongly dependent on the particular deposition technique adopted.
We investigated the effects of the addition of relatively small amounts of nitrogen, less
than 10%, on the UV-visible (vis)-near infrared (NIR) optical properties of a-SiC
xN
y thin films deposited by pulsed laser
ablation of SiC in presence of a controlled N
2 atmosphere.
← Variation of the refractive index n and absorpition coefficient of PLD deposited thin films as a function of the N content.
We observed that the nitrogen atomic fraction in the films was
dependent on the background nitrogen pressure during the deposition process. Nitrogen atomic fractions up to
7.5% were obtained. XPS results pointed out that nitrogen binds preferentially to Si and determines the contemporary and progressive
decrease of both the Si-C and Si-Si bonds. A slight increase of the sp
3 hybridized C-C bonds is also observed,
while the concentration of sp
2 bonded ones resulted in being affected less. Spectroscopic ellipsometry measurements showed the
evolution of the films optical characteristics. In particular, using both a multiple layers and an amorphous-like
dispersion model, optical band gap E
g values increasing from 1.6 up to 2.4 eV were obtained, with a progressive
decrease in the index of refraction values. The observed widening of the optical band gap as a
function of the nitrogen content was related with the progressive substitution of the weaker Si-Si bonds by
the stronger Si-C and Si-N ones. A mechanism involving the removal of electronic states lying at the band
edges, similar to what occurs in both hydrogenated silicon and silicon carbide materials, was suggested.
A relevant issue in fusion reactors is to choose materials for plasma facing components such that an acceptable lifetime is guaranteed. Silicon carbide is among
the very few materials that appear promising to resist harsh environmental conditions including high thermal loads, strong chemical erosion and severe energetic particle bombardment. Thin films, around 130 nm thick, of cubic silicon carbide
(β-SiC) were pulsed laser deposited on Si (100) substrates at 1173 K, at
fluences ranging from 3 to 9 Jcm-2. The films deposited at 6 Jcm-2 appear the most compact, homogeneous, crack free, with a reduced density of particulate
and droplets at the surface. Such films were irradiated by different plasmas, generated by ns and fs laser pulses respectively, corresponding to deposited intensities between 10 8 W cm-2 and 1018 W cm-2 . The compositional, morphological and microstructural evolution of irradiated β-SiC films were investigated
by energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), vibrational spectroscopies (IR and Raman) and transmission electron microscopy (TEM). Under both irradiation conditions the films remain well adherent to the substrates, showing thermal and mechanical stability. The samples
loose only a minor fraction of carbon. However, all irradiations induce meaningful changes of surface morphology, qualitatively different between the ns and fs pulses. In the
former an evident columnar structure develops at the crater edges; in the latter, after a single pulse, a wavy structure was observed whose
periodicity is nearly identical to the laser wavelength. Under both kinds of irradiation β-SiC shows meaningful chemical and structural stability in highly
energetic, aggressive plasma ambient.