APPLICABILITY OF TA GAAS SCHOTTKY PHOTODIODES PREPARED BY ION-ASSISTED PROCESSES/

The optical and electrical properties of Ta/GaAs Schottky photodiodes prepared by ion-assisted processes and followed by an appropriate ther mal annealing are discussed. Measurements of the short-circuit photocu rrent reveal photosensitivity from 400 to 880 nm, with a maximum stati c responsivity of 0.3 A W-1 at 750 nm. Ellipsometric measurements on t he Ta layer, which was partially oxidized during the thermal treatment , reveal that the refractive index n has a nearly constant value of 2. 2 in the spectral range 400-800 nm and that the extinction coefficient k is between 0.5 and 1, which is ascribed to the incomplete process o f oxidization. Based on the derived value of n and the known oxide lay er thickness, this layer is expected to be partially antireflecting in the vicinity of 400 nm. Considering all the available characteristics of these structures, we infer their applicability for use as photosen sors in the spectral range 400-880 nm.