MIKE ROSS wrote in a message to ROBERT SAYRE:

 MR> The problem is that the capacitance of a diode increases as its 
 MR> reverse bias voltage becomes smaller. 

Why is diode capacitance a problem?

 MR> The diode capacitance actually becomes a maximum just as it starts 
 MR> to conduct. 

Just before,  actually.  The junction still needs to be slightly
reverse-biased.  And the minimum reverse-bias gives the same effect as
having those capacitor plates *real* close together.

 MR> The choice of Schottky diodes is because they have a low forward 
 MR> voltage and can be made very tiny with very little capacitance.

Tiny in terms of the area of the junction?  Or something else?

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