FIELD AND HALL-EFFECTS IN SEMICONDUCTING YBA2CU3O6+DELTA

The field-effect mobility, Hall coefficient, and conductivity as functions of the oxygen concentration and temperature are reported for YBa2Cu3O6+delta films on the insulating side of the insulator-to-metal transition. The temperature dependence of the conductivity and Hall coefficient indicate that for small-delta the excess oxygen introduces acceptor states at about 30 meV above the valence-band edge. The field effect reveals a space-charge layer in which carriers are depleted at the air-YBa2Cu3O6+delta interface. The size of the field effect is limited by localized states at the interface.