Metal–Oxide–Semiconductor Field-Effect Transistor (MOSFET)
MOSFET are normally three terminal device such as source(S), gate(G), and drain(D)
Like other transistors it comes in two types N-Channel and P-Channel, where the N-Channel needs a positive voltage applied to its Gate(G) to turn the device on while the P-Channel needs a negative voltage.
MOSFET circuit symbols
All "FET"s are Voltage controlled, applying a voltage on the gate(G) instead of supplying a current to a bipolar transistor base(B) this causing the FETs resistance(VDS) between its Source(S) and Drain(D) to dramatically reduce.
MOSFETs are often higher power than general purpose and signal transistors due to the low power losses when used as switching devices due to their low on resistance.
Many Power Transistor MOSFET come in the TO220 packaging
MOSFET TO-220
The main parameters to look for on a MOSFET are its on resistance(VDS), Voltage Power and current limits, and its switching time, the gate voltage is less critical there are also dual gate MOSFET devices with two gate pins (total of 4 pins)
Logic level MOSFETs
Useful MOSFETs for the Arduino anr the Logic level ones that switch with a Vgs of less than 3.2 Volts
MTP3055VL Data sheet PDF
N-Channel Logic Level Enhancement Mode Field Effect Transistor with a Vds(on) of 2.7 Volts giving an Rds of 0.1 ohms(Ω)
NDP6020P Data sheet PDF
P-Channel Logic Level Enhancement Mode Field Effect Transistor RDS(ON) = 0.075 ohms(Ω) @ VGS= -2.5 V
Logic Level MOS FET Basics