Anisotropic direct-to-indirect band gap transition in shock- and ramp-wave compressed GaAs

Gallium arsenide (GaAs) is an important material for laser diodes, light emitting devices, and high-speed electronics. Strain-induced electronic band structure changes affect the performance of multi-layered GaAs-based devices. In the present work, effects of uniaxial strain on the low-temperature photoluminescence of GaAs were investigated using shock and ramp wave compression along the [100], [111], and [100] orientations. Uniaxial strain transformed GaAs from a direct-gap to an indirect-gap semiconductor, dramatically altering its optical properties. Unlike hydrostatic pressure, uniaxial strain along [111] produces a large splitting of the $L$ band. This causes the $L$-band minimum to plunge downward, resulting in a novel ``$L$-gap'' semiconductor.