Indirect band-gap transitions in GaP shocked along the [100], [110], and [111] axes

Shock compression experiments were performed to investigate optical changes in GaP under uniaxial strain. Low-temperature transmission spectra of sulphur-doped GaP samples were obtained at longitudinal stresses up to 5 GPa for shock wave loading along the 100 , 111 , and 110 orientations. At low uniaxial strains, changes in the band-gap absorption edge were consistent with the calculated band-gap shifts using the published deformation potentials. At high uniaxial strains, however, the published deformation potentials overestimated the shifts. This observation was confirmed by photoluminescence spectroscopy of S bound excitonic lines in shocked GaP:S. In addition, at strains higher than a few percent, a reduction in the intrinsic excitonic contribution to the band-gap absorption was obtained by modeling the absorption data with indirect-transition theory.