Investigation of defects in BaSi2 thin film on Si prepared by co-sputtering technique

Defects in undoped BaSi2 thin films prepared by co-sputtering technique were investigated. The growth rate ratio between the sputtering of Ba and BaSi2 targets (GR(Ba)/GR(BaSi2)) was varied between 0 and 0.5. Sample i (GR(Ba)/GR(BaSi2) = 0) exhibited a large root-mean-square (rms) roughness of 102 nm due to the presence of high density of 3D features which is attributed to Si precipitates. The rms roughness was significantly reduced to 9-26 nm for samples grown at GR(Ba)/GR(BaSi2) > 0.18. Raman data reveal the presence of Si vacancy (V-Si) and Ba antisite (Ba-Si) defects. For GR(Ba)/GR(BaSi2) > 0.18, the A(g) mode becomes blueshifted while the linewidth becomes narrower, suggesting a reduction in V-Si. A similar trend was also observed for Ba-Si. At 10 K, defect-assisted emissions were observed from sample i with photoluminescence (PL) peak energy of 0.92 and 1.27 eV. Power dependent PL analyses suggested that the emissions were due to V-Si-to-Ba-Si and V-Si-to-free hole transitions. However, samples grown at GR(Ba)/GR(BaSi2) >= 0.18 showed negligible PL emission, possibly due to low density of V-Si. Based on the Tauc and Urbach tail analyses, the band gap of all samples is similar to 1.31 eV, regardless of the GR(Ba)/GR(BaSi2). However, samples with less structural disorder showed smaller characteristic energy of the absorption edge (E-o).