1. In lasers , there is no forward bias ??However I do agree if there is an accelerating voltage to excite the more gas molecules to acheive population inversion
2. The free charge carriers means not bound to the particular atom . It also mean mobile charge carriers.
3. In the depletion zone, the immobile ions set up electric field . No immobile charge carriers ???The p region where the n region meet makes diffusion possible ,
3. Photons provides the energy for the electron to overcome band gap to jump into conduction band which may otherwise by very high (high resistance) . Thus light photon sets free electrons and decreases the resistivity of the semiconductor .
