Contact on substrate of a MOSFET
FETs are often used as Ideal Diodes when RdsOn is &lt;&lt; lower than the load R unlike Schottky diode which have a low threshold but higher Rs than Silicon.  So adding a diode in series would degrade the typical performance for losses as a switch. 

We can compare cost, size, power, speed , voltage drop, max current to compare a power Schottky power diode with a power FET. There is no advantage with a Schottky contact.

Low RdsOn FET 1.8mOhm @ 29A = 52mV , max cont. = 185A (/w heatsink)  &lt; $1 in volume  

High current Schottky FET  630mV @ 30A max cont. current  &lt; $0.50 in volume      


but its "contact" ...
making it much smaller increases diode series Rs=ΔV/ΔI based on smaller power capacity. Rs[Ω] ~0.5/Pd [W]max for most diodes +/-50%
whereas RdsOn above is Rs=0.0018Ω and Pd max= 108W +Hsink


 is as big as the FET.