Influence of the deposition parameters on the electronic and structural properties of pulsed laser ablation prepared Si1−xCx thin films

Abstract

Si 1 − x C x thin films have been 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. Both deposition temperature and laser fluence were increased up to 1150K and 14J∕cm2, 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. The film formation mechanism has also been qualitatively discussed on the basis of the subplantation model proposed by Lifshitz et al. [Phys. Rev. Lett. 62, 1290 (1989); Phys. Rev. B 41, 1046 (1990)].

Amorphous to crystalline phase transition in pulsed laser deposited silicon carbide

“…This value is close to the one reported for the stretching mode of Si-C bonds in crystalline SiC [27], but is blue-shifted with respect to the TO phonon vibration of 3C-SiC that is well known to occur at 796 cm À1 [32]. Such a shift to higher wavenumbers has been previously observed for PLD [20,22,33] and ion-beam deposited SiC films [34] but its origin requires more investigation. Size effects, such as phonon confinement due to the presence of SiC nanocrystals, cannot explain the detected deviation, as they would lead to a shift to lower wavenumbers [35].…”

“…This can be explained by the fact that at low temperature (below 600 8C), the surface atomic mobility of the impinging ablated species is reduced, which leads to the formation of amorphous films. At higher values of T d , the incident species have a greater probability of reaching thermodynamically favored sites thereby promoting the formation of SiC bonds [20,33]. The sharp transition in the nanostructure of the films, as detected by FTIR, takes place at a deposition temperature that is lower than the one corresponding to the appearance of the XRD peaks ($800 8C).…”