They could be any or all of those. There are many devices that can live in a so-called "TO-220" package, which to be accurate, is the second from the right.
They could be dual diodes, darlington transistors, regular transistors, voltage regulator chips, triacs, silicon controlled rectifiers, or MOSFETS, probably a few others that escape me at this moment. Can't tell by the package. They are in those larger-than-the-smallest-package type of package because they handle modest amounts of power, which implies that they produce heat which has to be radiated away by attaching them to a heat sink. That's what the tab on the TO-220 item is for, unless the little tab of metal, all by itself, is enough of a heat sink. It often is.