Abstract

GaAs-Schottky-diodes are a key-element of millimetre-, submillimetre-wave and THz-frequency mixer and multiplier systems. This paper presents the evaluation of sub-micrometer-size Pt/n-GaAs anode fabrication technology based on electrochemical metal deposition for planar Schottky-diodes. The technological approach for low-noise Pt/n-GaAs Schottky diode fabrication has been first optimised for whisker-contacted diodes and then successfully transferred to the fabrication of planar structures using a “dummy anodes” structural approach. The IF-noise temperature of planar diodes is significantly lower than that of whisker-contacted diodes. Excess noise of whisker-contacted anodes is attributed to temperature effects which are reduced in the planar quasi-vertical design. The effect of thermal annealing on IF noise temperature of planar structures is investigated using a “single step” method. In contrast to non-annealed samples, no evident threshold of the noise temperature is observed up to 3mA of bias current for thermally annealed samples. This strongly suggests that RIE-induced defects in the GaAs surface may generate trap noise at a few GHz. However this can be effectively reduced by thermal annealing. The optimisation of the fabrication technology results in very good DC-characteristics and excellent noise temperature of planar Schottky diodes for THz mixer applications.