Optical anisotropy of excitons in strained GaN epilayers grown along the 〈101¯0〉 direction

We calculate the spectroscopy of $1s$ excitons in GaN epilayers grown with biaxial stress on 〈101{}0〉-oriented M plane. In contrast to the growth on conventional C-plane substrates, for which we predicted five radiative excitons, we now demonstrate the existence of nine radiative transitions. $A,$ $B,$ and C excitons are now radiative for any polarization case, due to the crossed configuration of the wurtzite crystal field and the built-in strain one. In particular, the A exciton is significantly coupled to the electromagnetic field in {π} polarization (E∥c). Strong in-plane anisotropy of the optical response is predicted and computed.