Phonon deformation potentials of hexagonal GaN studied by biaxial stress modulation

In this work, a biaxial stress modulation method, combining the microfabrication technique, finite element analysis and a weighted averaging process, was developed to study piezospectroscopic behavior of hexagonal GaN films, epitaxially grown by metalorganic chemical vapor deposition on c-sapphire and Si (111) substrates. Adjusting the size of patterned islands, various biaxial stress states could be obtained at the island centers, leading to abundant stress-Raman shift data. With the proposed stress modulation method, the Raman biaxial stress coefficients of $E_2^H$E2H and A1 (LO) phonons of GaN were determined to be 3.43 cm-1/GPa and 2.34 cm-1/GPa, respectively.