Expansion of the electron-hole liquid plasma at GaAs surface

The spectral and planar distribution of the luminescence intensity of the electron-hole plasma (EHP) created by laser excitation in the subsurface region of a direct-band semiconductor like GaAs in contact with a dielectric medium (Si3N4) is studied. High optical excitation levels (L approximately 5 MW/cm2) make possible to detect: (1) the appearance of stimulated radiation mainly from the regions of the sample edges; (2) the expansion of EHP from the excited region predominantly along the GaAs-Si3N4 interface up to a distance (l approximately 50 to 100 μm), which is several times greater than the corresponding bulk value. The assumption is made that the electron-hole liquid is created not only at the 'tails' of the expanded plasma, but also within the excited regions (in the latter case after a partial cooling of EHP, when in the process of the relaxation the electron-hole pairs concentration achieves the EHP-condensation value n approximately 1016 cm-3). The mechanism of a long-wave range tail formation in EHL radiation, which is caused by the energy losses on non-equilibrium plasmons, is discussed. (author)