NMOS FET with a negative drain
All MOSFETs inherently have a body diode between source and drain. This diode is reversed biased under normal usage, but if you put the drain at a lower potential than the source on an N-channel FET, you will, as you have discovered, forward-bias this diode.







simulate this circuit &ndash; Schematic created using CircuitLab

More on the body diode: MOSFET: Why the drain and source are different?

You will have to find a way to place the MOSFET in your circuit such that the drain is at a higher potential than the source. Or, you can use a P-channel MOSFET, where the drain must be at a lower potential than the source.

Either way, you will likely need some sort of level-shifting circuit to translate your 0V-3V logic input to whatever levels are required by the MOSFET arrangement you select. This can be as simple as another transistor (usually a cheap BJT) and a resistor, or a complicated arrangement designed to switch the MOSFET at very high speeds which might include dozens of components and maybe even additional voltage supplies. It all depends on your application.