Stoichiometry-controlled growth of Ba _xSr _1-xTiO ₃ thin films and their electrical behavior in heterojunction assemblies

We describe an optimized chemical synthesis route to obtain Ba _xSr _1-xTiO ₃ (x = 0, 0.50, 0.67, 1.0) thin films with impeccable stoichiometry control. The molar ratios of the precursors were altered to produce the cubic phase of SrTiO _3, Ba _0.5Sr _0.5TiO ₃, Ba _0.67Sr _0.33TiO ₃ and the tetragonal phase of BaTiO ₃ thin films on single crystalline p-Si (100) and quartz substrates. The obtained Raman spectra for the Ba _xSr _1-xTiO ₃ thin films on quartz substrates showed characteristic vibration modes at ∼303, 515 and 716 cm ^-1. The active modes of BaTiO ₃ signify the tetragonal phase, which is important for its various technological advantages. The significant features of these materials were obtained through capacitance-voltage (C-V) measurements with Pt (or Ag)/Ba _xSr _1-xTiO ₃/p-Si/Pt (or Ag) assemblies, at 1, 10 and 100 kHz. Substantial hysteresis (ΔV) of 315 mV (with Ag) and 219 mV (with Pt) was observed for Ba _0.5Sr _0.5TiO ₃, whereas for BaTiO ₃ and SrTiO ₃ the obtained hysteresis was 256 mV and 96 mV, respectively. The largest hysteresis of 793 mV was observed for SrTiO ₃ with a Pt electrode. The above findings are important for assessing the device compatibility of cost efficient solution processed Ba _xSr _1-xTiO ₃ thin films.