Nanocrystalline SiC formed by annealing of a-SiC:H on Si substrates: A study of dopant interdiffusion

Nanocrystalline silicon carbide (nc-SiC) is an interesting material for electronics applications, both in its own right and as a host matrix for silicon quantum dots. When synthesized by annealing of a-SiC:H on Si substrates, interdiffusion of dopants occurs if either the a-SiC:H or the Si substrate is doped. Annealing a-SiC:H on highly boron-doped substrates at 1100 C leads to a fairly homogeneous doping level of 41019 cm3 throughout the nc-SiC film. An unexpected anomaly in secondary ion mass spectroscopy quantification is observed and a method to circumvent it is shown. The nanostructure of the nc-SiC is only weakly affected as most of the diffusion occurs after the onset of crystallization. Annealing of doped a-SiC:H on Si substrates at 1100 C leads to strong free carrier absorption at infrared wavelengths. This is demonstrated to originate from dopants that have diffused from the a-SiC:H to the Si substrate, and a method is developed to extract from it the doping profile in the Si substrate. The detection limit of this method is estimated to be 61013 cm2. Doping levels of (0.5-3.5)1019 cm3 are induced at the Si substrate surface by both boron and phosphorus-doped a-SiC:H. When the Si substrate is doped opposite to the a-SiC:H p-n junctions are induced at a depth of 0.9-1.4 lm within the Si substrate for substrate resistivities of 1-10 X cm. Implications for different solar cell architectures are discussed. Dopant diffusion can be strongly reduced by lowering the annealing temperature to 1000 C, albeit at the expense of reduced crystallinity.VC 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4890030]