Influence of Deposition Conditions on the Characteristics of Luminescent Silicon Carbonitride Thin Films

Abstract

The influence of the substrate temperature and argon gas flow on the compositional, structural, optical, and light emission properties of amorphous hydrogenated silicon carbonitride (a-SiC x N y :H) thin films were studied. Thin films were fabricated using electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR PECVD) at a range of substrate temperatures from 120 to 170 • C (corresponding to deposition temperatures of 300 to 450 • C) in a mixture of SiH 4 , N 2 , and CH 4 precursors. Variable angle spectroscopic ellipsometer (VASE), elastic recoil detection (ERD), and Rutherford backscattering spectrometry (RBS) verified optical bandgap widening, layer densification, and an increase of the refractive index at higher substrate temperatures. The microstructure of a-SiC x N y :H z thin films was determined by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy. The substrate temperature strongly affected the binding state of all atoms, and in particular, carbon atoms attached to silicon and nitrogen, as well as hydrogen-terminated bonds. We correlated the films' microstructural changes to a higher species' mobility arriving on the growin layer at higher temperatures. Photoluminescence (PL) measurements showed that the total intensity of visible light emission increased. A systematic blueshift of the centroid of the wide PL peak was observed following the increase of optical gap. 2 This is a consequence of their unique properties inherited from the combined properties of binary substructures, silicon carbide (SiC), silicon nitride (SiN), and carbonitride (CN). On the one hand, the durability and hardness of SiN structures cannot compete with those of carbon-based hard counterparts such as diamond-like carbon (DLC), CN, and SiC materials.3 On the other hand, carbon-based films do not offer the required properties for current optical designs, 4 while SiN thin films have been considered as the basis for several optoelectronic devices. 5 The protective properties of SiC x N y materials appear as an intermediate matrix to meet the demands in hard coating technology and concurrently, the tunability of SiC x N y 's electrical and optical properties raises its interest in the field of Photonics. SiC x N y structures have appeal to researchers for wear-resistant 6 and corrosion-resistant coatings, 7 and recently, for silicon-based anode materials in lithium ion batteries. 8 In addition, SiC x N y structures are used for gate dielectrics in thin film transistors 9 and diffusion barriers.10 They appear to broaden the optical parameter space required for the application of ultraviolet (UV) detectors 11,12 and the passivation layer in the third generation "all-silicon" tandem solar cells. 13,14 To this end, Chen et al. reported a direct bandgap of 3.8 eV for c-Si 2 N 4 C 15 and Azam et al. 16 investigated the tunability of the bandgap depending on the dominant phase present in the SiC x N y layer. We previously showed that the visible photoluminescence (PL) emission from ...

X-ray Absorption Spectroscopy of Silicon Carbide Thin Films Improved by Nitrogen for All-Silicon Solar Cells

“…The presence of C-H bonds can be expected in our CVD-grown SiC and SiCN samples containing significant amounts of hydrogen coming from SiH 4 and CH 4 gases during the deposition. 18 Another difference between SiC and reference graphite is an additional feature at ∼286.9 eV (Peak 2) in SiC, which is also observed in asdeposited SiCN samples. This feature is attributed to both the transition of 1s to π* of carbon in C≡N bonds and C-H bond σ transitions.…”

“…It should be noted that as-deposited samples are all amorphous as previously determined by XRD and TEM techniques. 18,23 Thin film composition.-We employed graphite substrates, which enables the detection of well-distinct signals from light elements contrary to the silicon substrates commonly used for such films. Figure 1 shows the constituent elements (hydrogen is excluded) with their low uncertainty as a function of N 2 to CH 4 flow rate during the deposition.…”

“…ECS Journal of Solid State Science and Technology, 2020 9 083002 Optical properties.-We previously explained the details of the analysis of the refractive index and optical bandgap and the accuracy of the models used for amorphous SiCN thin films. 18 Figure 2 shows the bandgap and refractive index as a function of relative N 2 to CH 4 gas flow rates. In agreement with the observed blue shift of the PL emission (Fig.…”

“…More details on the configuration of the system are reported elsewhere. 18 The gas flow rates of SiH 4 and CH 4 for all samples were held constant at 5 sccm (standard cubic centimetres per minute) and 4 sccm, respectively, which resulted in the growth of virtually stoichiometric SiC. 19 Following deposition, all samples were subjected to post-deposition annealing in a quartz tube furnace for 60 min in a N 2 atmosphere at temperatures ranging from 300 to 1200 °C.…”

“…The ellipsometry data were fitted using a Cauchy model delivering the refractive index (n) as a function of wavelength (λ) and extinction coefficient (k) as an exponential absorption function via the dispersion relation. 18 Synchrotron radiation beamlines at the Canadian Light Source (CLS) facility located at the University of Saskatchewan were used to collect XANES spectra. The absorption spectra were recorded simultaneously in total electron yield (TEY) and X-ray fluorescence yield (FY).…”