Do modern aircraft have the functionality for the pilots to look behind the aircraft?
Some do, some don't.

It depends by the type of the aircraft and by the need to see behind the aircraft itself.

Just as an example, this is a render of a Boeing F/A-18E "Super-Hornet" cockpit:

 

On the canopy's frame are located three adjustable mirrors (like the one on the windshield of a car) the pilot can use to see what's happening behind him.

As already stated in comments, aircraft usually don't "power-back" and there is no overtaking like in cars (where cars from behind can overtake you just from left or right), so usually there is no need of mirrors inside a cockpit.

In a military aircraft, mirrors increase your situational awareness, but


with a wide Field-of-View (FoV), details or a distant aircraft or missile cannot be seen
with a narrow FoV, a smaller portion of the sky is visible


Just for reference, the F-16 or the F-22, both featuring a single piece canopy, don't have rear view mirrors. The pilot must turn the head as much as he/she can and look behind.