Influence of surface quality on tunneling and electrical properties of NdCeCuO thin films

Thin films of Nd_1.85Ce_.15CuO_4-y were prepared by laser ablation on heated SrTiO₃ substrates in 150 mtorr O₂. After deposition, the films were annealed in vacuum at 820°C. This step is necessary in order to achieve bulk superconductivity in the samples, but it has a deleterious influence on their surface properties. Tunneling characteristics measured on such samples show very broad features, making a determination of the gap very difficult. A very high contact resistance resulted in difficulties with Hall and magnetoresistance measurements. To remedy these problems, the influence of different etches and surface treatments was studied. Specifically, the electrical properties and tunneling characteristics of Au contacts made on acid-etched and ion-milled NdCeCuO thin films were measured. In the case of acetic acid, the current through the contact at low temperatures was shown to be due to tunneling, and the slow temperature dependence makes it likely that this is also the case up to room temperature. For ion-milled surfaces, very similar tunneling characteristics at low temperature were observed, but the temperature dependence suggests a change in the mechanism as the temperature is increased. Gold contacts prepared on acetic-acid-treated surfaces of NdCeCuO thin films have made it possible to measure magnetoresistance and Hall effect from room temperature to 4.2 K, thus solving the initial noise problems encountered