What is the difference between an exciton binding energy and orbital binding energy? I can see no difference between them since when an exciton is created, the electron is excited to the next (or one of the next available states) and an orbital binding energy is the amount of energy required to take an electron from it's current orbital excitation to the next available state of orbital excitation. It seems to be just the one and the same, just worded differently.
You may be right within the hydrogenic model of an exciton. This model implies that the exciton can be considered as a system being similar to the hydrogen atom, but with different masses of particles that are effective mass of the electron and hole. However, exciton is somewhat more complicated, it is, by definition, collective excitations of the electron-hole plasma. The hydrogen model allows you to get right position of exciton peaks only at 0 K temperature, but it does not give a clue why these peaks change with temperature and carrier concentration.
Below is a list of publications showing the collective nature of excitons. Actually, each quasi-particle in semiconductors results from collective effects.
- Haug H., Koch S.W., Quantum Theory of the Optical and Electronic Properties of Semiconductors, Wspc, 2009
- C.F. Klingshirn, Semiconductor Optics, Springer, 2012
The binding energy of an exciton is not the energy released when they recombine; it is the energy required to create a free electron and hole from it. The electron and hole were previously in a bound state, which was the exciton.
I think you might be speaking about the energy required to create an exciton. if that is E_B_ then E_g_ - E_B_ is the exciton binding energy.