AbstractThe band-gap shift of GaN:Mg epilayers on (0001)-oriented sapphire was studied as a function of uniaxial strain compression along the c-axis using time-resolved, optical absorption measurements in shock wave experiments. For longitudinal stresses ranging from 4 to 14 GPa, the band gap shift is approximately 0.026 eV/GPa. Combining this result with the known behavior of wurtzite GaN under hydrostatic pressure and biaxial stress, a new set of deformation potentials has been estimated: acz-D1 = -10.2 eV, act-D2 = -7.9 eV, D3 = 1.33 eV and D4 = -0.74 eV. A slow band gap shift is also observed following the immediate band gap increase upon impact. This phenomenon can be explained by a time-dependent screening of the piezoelectric field.