Si and SiC nanocrystals in an amorphous SiC matrix: Formation and electrical properties

Abstract

Layers of Si nanocrystals in a dielectric matrix have promising properties to be implemented as the absorber layer in a top cell of a Si‐based tandem solar cell. Si nanocrystals in SiC are produced by plasma deposition of Si rich a‐SiC:H and subsequent solid phase crystallization by thermal annealing at temperatures between 800°C and 1000°C. The Si rich a‐SiC:H films were doped with boron by addition of diluted diborane (B2H6 in H2) to the plasma process. The microstructure was investigated for different gas fluxes and annealing procedures and the films were found to consist of amorphous or polycrystalline SiC with embedded Si nanocrystals. The microstructural results are then correlated with the electrical and optoelectronic properties. By choosing appropriate deposition parameters, the films micro‐structure could be modified such that the crystallization of both Si and SiC nanocrystals is favoured and the conductivity is enhanced. X‐ray diffraction (XRD) patterns show the formation of both Si and SiC nanocrystals after annealing at 900 °C, if the hydrogen flux in the plasma is large enough. The formation of SiC nanocrystals is confirmed by Fourier Transformed IR (FTIR) spectra where a transition from a Gaussian shaped peak of the amorphous SiC‐phase to a blueshifted Lorentzian peak of nanocrystalline SiC is observed. Dark dc IV measurements reveal the increase of conductivity with diluted diborane flux from 9.32 10–6 Ω–1cm–1 to 1.98 10–2 Ω–1cm–1 for a 1000 °C anneal. Increase of annealing temperature at constant doping also increases conductivity by about two orders of magnitude. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural and optical properties of silicon nanocrystals embedded in silicon carbide: Comparison of single layers and multilayer structures

“…A c c e p t e d M a n u s c r i p t 23 Furthermore, both the interdot distance and the grain size distribution are less crucial for Si NC in SiC than for Si NC in SiO 2 [8,18]. Consequently, precise control of Si NC size and separation is not required, and as this study and other works [11,12,14] show that control over both is extremely difficult to obtain with the ML approach in the Si NC/SiC system, it follows that SRC SL might be more effective for optimising the optoelectronic properties of SiC with embedded Si NC for Si NC-based devices.…”

“…In addition, co-crystallization of Si and SiC NC is observed [22][23][24][25][26]. It was only recently that Summonte et al [12] managed to obtain size-controlled Si NC in SiC by optimizing the ML parameters: they proved using transmission electron microscope (TEM) images that for an as-deposited SRC thickness between 3 and 4 nm, the ML structure survives the annealing for both 3 nm and 9 nm thick SiC barrier layers.…”

“…The ML approach is known to work very well for Si NC size control in SiO2 [19][20][21] but is much more challenging in SiC because interdiffusion of the SiC barrier layer and the SRC well layer occurs [12]. In addition, co-crystallization of Si and SiC NC is observed [22][23][24][25][26]. It was only recently that Summonte et al [12] managed to obtain size-controlled Si NC in SiC by optimizing the ML parameters: they proved using transmission electron microscope (TEM) images that for an as-deposited SRC thickness between 3 and 4 nm, the ML structure survives the annealing for both 3 nm and 9 nm thick SiC barrier layers.…”