The diode is not added, it is inside the Mosfet.

 

When I was checking out the use of MOSFETs for the first time I used this circuit and plotted this graph:
View attachment 255778

View attachment 255779

Also Dave, what tools/simulator did you use for this?

 

I'd be interested to see that Dave with a diode added as Wendy has in her OP.

Ah, I initially just read the diode as part of the MOSFET symbol without paying any attention to the direction. Only now, on closer inspection, do I see that it looks like an external diode. Maybe my example wasn't directly relevant or helpful, sorry if that's the case.
Edit: changed internal to external. It looks external because of the dots where it joins the MOSFET

 

The diode is not added, it is inside the Mosfet.

And I'm assuming that it has been drawn the wrong way round by mistake.

 

If you simply want to see, observe, measure the device's behavior over a range of gate voltages, then remove the diode. That may have some purpose in some design you have

That represents the parasitic diode that is inherent in all MOSFETs. There are two and one gets shorted to the source in three terminal devices.

 

It looks external because of the dots where it joins the MOSFET

That's just the way @Wendy drew it. She uses some drawing program like Paint for her schematics.

 

That's just the way @Wendy drew it. She uses some drawing program like Paint for her schematics.

Ahh OK that's fine then, so Wendy's results are a curiosity...

 

Also Dave, what tools/simulator did you use for this?

I didn't use a simulator I used real components. I measured the two voltages with two cheap multimeters and then plotted the results with MS Excel.

 

the diode in question is built into the MOSFET.

 

the diode in question is built into the MOSFET.
View attachment 255799

You'll have to take the cover off and turn it round!

 

And I'm assuming that it has been drawn the wrong way round by mistake.

The drawing shows a P-channel Mosfet with its diode correct but the schematic does not show the power supply polarity which must be negative for the P-channel Mosfet.
But Wendy probably uses an IRF-540 N-channel Mosfet and a positive supply.