Unstrained GaN with Polar and Nonpolar Orientations

To determine Acr and Ago from the exciton transition energies for the unstrained C-plane GaN film, we apply Hopfield s quasicubic model developed for the wurtzite crystal structure [25]. The relation between the differences Sx,Y = Ex — Ey in the exciton transition energies and the splitting energies is 

For unstrained GaN, the crystal symmetry results in equal oscillator strengths 

Second, the B and C excitons are partially polarized in M-plane (A-plane) GaN films with values of pxz = 0.18 (py = 0.18) and Pxz = 0.47 (pyz = 0.47), respectively. If the A and B excitons are not spectrally resolved, the degree of linear in-plane polarization becomes pxz = 0.31 (py = 0.31) for both transitions together. Therefore, polarized light emission could be obtained 

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