Formation, coarsening and band gap engineering of sponge-like Si-SiO2 nanocomposites – materials design by theoretical predictions

It has been found by energy filtered transmission electron microscopy (EFTEM) that metastable SiOx≈1 films decay during thermal treatment by spinodal decomposition into a Si nanowire network embedded in SiO2 forming a nanocomposite [1,2]. This nanoscale material is promising candidate as absorber layer for next generation solar cells as it exhibits a widened band gap due to quantum confinement and electrical interconnectivity due to percolation of the nanostructured Si. The formation of Si-SiO2 nanocomposites was predicted by a kinetic Monte Carlo simulations [1,3]. Additionally, the band gap and the band offset of the nanocomposite were predicted by large scale atomistic pseudopotential computations [4]. Experimentally, the sponge-like morphology was verified by EFTEM and atom probe tomography [2], whereas its band gap measured via light absorption is still under discussion. The predicted morphology of the sponge-like Si-SiO2 nanocomposite appears to be almost identical to the measured ones. Also the predicted scaling behavior of the coarsening of the nanostructure during thermal treatment was verified experimentally. Combining theory with experiments delivers the understanding for tailoring the properties like quantum confinement of the sponge-like Si. [1] Müller, et al. Appl. Phys. Lett. 85, 2373 (2004) [2] Friedrich, et al. Appl. Phys. Lett. 103, 133106 (2013) [3] Liedke, et al. Appl. Phys. Lett. 103, 131911 (2013) [4] Keles, et al. Appl. Phys. Lett. 103, 203103 (2013)