Characteristics of Millimeter-Wave Schottky Diodes with Microcluster Interface

We present experimental evidence that a single Schottky diode on GaAs is an agglomerate of paralleled microjunctions with different barrier heights and saturation currents. The current-voltage characteristic of the cluster breakes up into sections of exponentials with different slopes as one cools the diode from 300 K to 10 K. Noise measurements performed on cooled diodes at 4 GHz also confirm that a single device is a cluster of paralleled diodes. The model suggests a more compl icated equivalent cicuit of the diode which can also explain some of the problems experienced in attempts to theoretically predict cooled mixer noise performance. It also explains why in some diodes the excess noise appears at lower currents levels than in other diodes, a phenomenon which seriously degrades the low noise preformance of the mixer.