In a semiconductor it requires energy equivalent to the band gap energy ($E_g$) to excite an electron to the conduction band. This gives rise to an exciton (conduction electron-valence hole pair). The energy released when these recombine (exciton binding energy, $E_B$) is said to be slightly lower than the band gap energy.
Here are my questions:
Why is $E_B$ lower than $E_g$?
Where does the energy difference $E_g - E_B$ go in the process of forming an exciton?
I have noticed this question as a possible duplicate, but the answer doesn't really say more than "It is very complicated". Is there no sensible way to get at least an intuitive understanding of these questions?