Optical properties of thick-film GaN grown by hydride vapor phase epitaxy on MgAl 2 O 4 substrate

A hydride vapor phase epitaxy was employed to grow the 10∼240 µm thick GaN films on a (111) MgAl2O4 substrate. The GaN films on a MgAl2O4 substrate revealed characteristics of photoluminescence (PL) in impurity doped GaN, which may be due to the out-diffusion and auto-doping of Mg from the MgAl2O4 substrate during GaN growth. The PL peak energy of neutral donor bound exciton emission and the frequency of Raman E2 mode were decreased by increasing the GaN thickness, due to the residual strain relaxation in the epilayers. The dependence of Raman E2 mode of GaN films on residual strain can be estimated as Δ ω/Δ σ=3.93 (cm−1/GPa).