This paper describes in detail the general properties of Schottky diode and SIS mixers. Their performances when used in low noise mm and sub-mm wave receivers are compared and a brief attempt is made to identify possible limitations and future improvements.
E. Kollberg, E. Kollberg,
"Superconducting vs Schottky Mixers For mm and sub-mm Waves", Proc. SPIE 0598, Instrumentation for Submillimeter Spectroscopy, (21 April 1986); doi: 10.1117/12.952312; https://doi.org/10.1117/12.952312