Is there such thing as an absorbing/diffusive door?

[kthulhutu]

One of the non-idealities in my room is that of a hollow-core door located in the right rear corner.
Obviously, we can't go getting rid of the doors to our rooms. But I also can't mount a panel on it because it needs space to open and close.
I already know that solid-core (or even heavier) doors are the way to go for soundproofing. But in consideration of the acoustics inside the room, are there any particular door designs that work well or at least better than hollow core doors for absorbing or diffusing incident sound?

 

[firedog]

I read somewhere once about sound absorbing material that you could hang on/over a door.

 

[Kal Rubinson]

I have such a door in the right front corner of my room and I just leave it open.

 

[alex-z]

Sure, you could mount some diffusion or absorption to the back of the door, leaving a gap so the hinge still swings.

But how much surface area does the door have relative to your whole room? Unless the door happens to be a first reflection point, it really doesn't matter.