Deposition and tunneling phenomena of dc sputtered BiSrCaCuO-based heterostructures

We have produced Bi₂Sr₂CaCu₂0_8+δ/ Bi₂Sr₂YCu₂0_8+δ/Bi₂Sr₂CaCu₂0_8+δ herostructures using a high pressure dc sputtering technique. The films have been deposited in situ at high oxygen pressure on (001) SrTi0₃ substrates. X-ray diffraction and high resolution transmission electron microscopy (WRTEM) showed highly c-axis oriented trilayers. TEM analysis showed sharp interfaces between the superconducting films and the barrier, without intermediate amorphous regions. The Bi₂Sr₂CaCu₂0_8+δ layers had superconducting transition temperatures of 87 K, with ΔT_c⩽1 K, while the barrier layers showed a semiconductor-like behavior explained in terms of variable range hopping process. At low temperatures the conductance versus voltage characteristics exhibit peaks indicative of gap-like structures at about ±30 mV, finite conductances at zero bias and flat backgrounds for energies higher than 30 mV.