Poly(vinyl pyrrolidone)-Assisted Sol−Gel Deposition of Quality β-Barium Borate Thin Films for Photonics Applications

β-Barium borate (β-BaB 2 O 4, β-BBO) films were deposited on fused silica substrates by spin coating poly(vinyl pyrrolidone) (PVP)-modified metallo-organic solutions. Film thicknesses of more than 500 nm were obtained by a single spin-coating step followed by O 2 plasma and thermal treatments. Crack formation was effectively suppressed by the introduction of PVP. Samples annealed at 650 °C exhibit high transparency over a wide wavelength range (1100 nm−210 nm) and have a preferred orientation corresponding to the (006) crystallographic direction. The increased thickness of the BBO films provided a >10-fold increase in the second harmonic generation (SHG) efficiency when compared to BBO layers fabricated without the addition of PVP and O 2 treatment. The precursor gels are readily amenable to contact lithography leading to patterned β-BBO films.