The SUPFET, a new photodetector with ultrathin YBaCuO/PrBaCuO multilayer channel

Several electric field effect devices have been built with YBaCuO/PrBaCuO layers and multilayers; The layers are deposited by an inverted cylindrical magnetron sputtering process (ICM) on MgO substrates. This process 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 nominal thickness of each material of about 4 nm. Small channel geometries of 50/spl times/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. These devices are tested in static and dynamic measurements: the silicon dioxide layer inhibits symmetric I-V characteristics of the dielectric layer with high breakdown field strength up to 4 MV/cm. The gate capacity of a few pF allows the test of the device 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 results of these field effect experiments are compared with optically induced effects. The optical measurements are performed with a helium-neon laser (633 nm) with a power density of 600 W/cm/sup 2/. The laser pulses with frequencies up to 1 MHz give responses somewhat similar to the observed field effect responses. Combining field effect and optical irradiation, it Is found that the laser pulses seem to create charge carriers, screening the field effect. Based on this principle a new photodetector is proposed.<>