What is the formation energy of a defect? What does it mean in physics?

[smokefly]

I am reading some theoretical papers on the defects in semiconductors. Theorists can calculate the formation energy of a certain kind of defect. If the number is too big, this defect is very unlikely to be seen. So what does this “formation energy” mean? Is that the energy necessary to move atoms together to form this defect, which is also the energy necessary to keep the defect structure from dissociating? That's my understanding but I don't know if it is correct or not.

 

[Mapes]

The formation energy is the difference in the total crystal energy before and after the defect arises. It represents the penalty in broken atomic bonds and in lattice stress. Opposing this energy penalty, however, is the increase in entropy because a crystal containing a defect has more possible microstates than a perfect crystal. Does this help?

 

[smokefly]

Thanks a lot for the clear image. It helps a lot.

The formation energy is the difference in the total crystal energy before and after the defect arises. It represents the penalty in broken atomic bonds and in lattice stress. Opposing this energy penalty, however, is the increase in entropy because a crystal containing a defect has more possible microstates than a perfect crystal. Does this help?