Strain Dependence for Nonpolar Orientations of GaN

For nonpolar orientations, the GaN films are usually grown on LiAl02, l -plane sapphire, and A- or M-plane SiC so that the strain due to the lattice mismatch 

Optical Polarization Anisotropy in CaN Films and (ln,Ca)N/CaN Multiple Quantum Wells 

Strained CaN Films with DifTerent Nonpolar Orientations 

For sample III, the transition energies calculated for the strain values of Sxx = —0.73% and Szz = —0.22% agree quite well with the measured ones. The calculated oscillator strength offx = 0.98 Ifz = 0.94) suggests that the Ti (T2) transition is almost completely x polarized (z polarized). Because of the smaller thickness of sample IV in comparison to sample III, Syy in sample IV 

A similar analysis as performed for low temperatures leads to the results at room temperature listed in Table 7.3. Note that the strain values are different from the ones at low temperature owing to the different thermal expansion coefficients of the film and substrate material. 

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