THE SUPFET, A NEW PHOTODETECTOR WITH ULTRATHIN YBACUO PRBACUO MULTILAYER CHANNEL/

Several electric field effect devices have been built with YBaCuO/PrBa CuO layers and multilayers; The layers are deposited by an inverted cy lindrical magnetron sputtering process (ICM) on MgO substrates. This p rocess has been proved to give very good performances even for thinner and ultra thin films. The films used for the field effect transistor devices consist of one or two bilayers of YBaCuO and PrBaCuO with a no minal thickness of each material of about 4 nm; Small channel geometri es of 50 microns x 60 microns are etched by argon ion milling and the channel is covered by a silicon dioxide dielectric layer (50-100 nm). The gate contacts as well as the drain and source contacts are made by sputtered gold pads. Theses devices are tested in static and dynamic measurements : the silicon dioxide layer inhibits symmetric I-V charac teristics of the dielectric layer with high breakdown field strength u p to 4 MV/cm. The gate capacity of a few pF allows the test of the dev ice in a kHz frequency range. Tests with sine wave gate voltages show low distortion of the output signal with a voltage gain of about 0.01. Smaller dielectric layers could raise the gain close to one. The resu lts of these field effect experiments are compared with optically indu ced effects. The optical measurements are performed with a helium-neon laser (633 nm) with a power density of 600 W/cm(2). The laser pulses with frequencies up to 1 MHz give responses somewhat similar to the ob served field effect responses. Combining field effect and optical irra diation, it is found that the laser pulses seem to create charge carri ers, screening the field effect. Based On this principle a new photode tector will be proposed.