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 (GRBa/GRBaSi2) was varied between 0 and 0.5. Sample i (GRBa/GRBaSi2 = 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 GRBa/GRBaSi2 > 0.18. Raman data reveal the presence of Si vacancy (VSi) and Ba antisite (BaSi) defects. For GRBa/GRBaSi2 > 0.18, the Ag mode becomes blueshifted while the linewidth becomes narrower, suggesting a reduction in VSi. A similar trend was also observed for BaSi. 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 VSi-to-BaSi and VSi-to-free hole transitions. However, samples grown at GRBa/GRBaSi2 ≥ 0.18 showed negligible PL emission, possibly due to low density of VSi. Based on the Tauc and Urbach tail analyses, the band gap of all samples is ∼1.31 eV, regardless of the GRBa/GRBaSi2. However, samples with less structural disorder showed smaller characteristic energy of the absorption edge (E o).