Charge transport in amorphous and tetragonal semiconducting YBaCuO films

Abstract

We have explored the charge transport mechanisms in six different YBaCuO semiconducting thin films in the temperature range of 70 K to room temperature. Two of the samples were deposited on LaAlO3 substrate and were tetragonal with the composition of YBa2Cu3O6.5 and YBa2Cu3O6.3. The other four were amorphous as-deposited on Si substrate with and without a MgO buffer layer, and on an oxidized Si substrate with and without a MgO buffer layer. All tested films exhibited semiconductor-type resistance vs. temperature characteristics with increasing resistance as the temperature was decreased. Around room temperature all six samples had thermally activated transport characteristics that was interpreted as activation of hole-like carriers from localized states around the Fermi level to extended states. As the temperature was decreased, two tetragonal samples went through a transition to a variable range hopping-like conduction. The amorphous ones remained within the thermally-activated transport regime in the temperature range of 253 K to 318 K, with EA ≈ 0.2 eV.