Probing structural alterations in shock compressed GaAs

Bandgap engineering through the control of strain can be accomplished through many means, such as applying strain epitaxially that typically requires complicated growth and/or material processing. An alternative is applying a one-time shock wave to GaAs, transforming the material to a precisely controllable, permanently pressurized structure. In this study, laser-driven flyer plate experiments were conducted in crystalline GaAs to probe permanent structural changes induced by shock compression. Detailed characterizations after the shock were conducted at the center of the compression through photoluminescence (PL), time-resolved PL, x-ray diffraction (XRD), and Raman spectroscopy. While PL peak positions shifted nonlinearly with increasing pressure, the peak linewidths increased linearly. PL lifetimes shortened with the application of pressure, showing evidence of more defects. The XRD displayed peak shifts and peak broadening with increasing pressure, with a possible systematic decrease in crystallite sizes. The observed transverse optical (TO) and longitudinal optical Raman modes showed nonlinear peak shifts, while the TO mode exhibited linewidth broadening. The results indicate the presence of strong disorders and a high degree of inhomogeneous strain in the shocked material. The compressed GaAs appear to have highly localized regions with smaller grains.