Deposition of hydrogenated nanocrystalline silicon carbide by ECR-CVD

Abstract

In this work we report on the deposition of hydrogenated nanocrystalline silicon carbide (nc-SiC:H) films using an electron cyclotron resonance chemical vapor deposition (ECR-CVD) system with silane (SiH 4) and methane (CH 4) as source gases. It was found that the conditions of strong hydrogen dilution and high microwave power are necessary for the fabrication of nanocrystalline SiC grains, which are found to be embedded in an amorphous matrix. The films have been studied using high resolution transmission electron microscopy, infrared absorption, Raman scattering and x-ray photoelectron spectroscopy. All the results have confirmed the prescence of SiC nanocrystallites. Very strong photoluminescence (PL) could be observed from these films at room temperature, with a peak energy of 2.64 eV. This energy, being higher than the optical bandgap of 3C-SiC, can be possibly due to quantum size effect in these crystals, which are embedded in an amorphous matrix of larger bandgap. Time-resolved PL at the peak emission energy exhibits a bi-exponential decay process with lifetimes that are in the order of picoseconds and nanoseconds, which are at least 2 orders of magnitude faster than that of bound excition transitions in bulk 3C-SiC at low temperature. The strong light emission and short PL lifetimes observed strongly suggest that the radiative recombination is a result of direct optical transitions in the SiC nanocrystallites. It was found that upon ultraviolet irradiation using an Ar + laser (351 nm), the PL intensity of the films was enhanced. After 20 minutes of irradiation, the PL intensity increased by about three times. This result suggests that the UV light may lead to modification of nonradiative recombination centers in the films.