I have a circuit that requires to switch on/off the load using arduino control signal. The load uses 5V DC and upto 3A current. MOSFET or relay must be used to switch the load supply on/off. Input to my circuit is continuous 5V DC.

Which should I use either a relay or MOSFET?

I have used IRF540 MOSFET which works but after it switches on the load voltage is only 3V, which is very less power to the load.

If I have to use a MOSFET what type of MOSFET is preferrable?