(a) Schematic representation of optical pumping in a semiconductor material: a pump photon of energy is absorbed in the semiconductor material creating an electron-hole pair. The electron and hole cascade to the bottom of the bands releasing extra energy to the lattice and eventually recombine either radiatively or nonradiatively. (b) (after [67]): Layer widths of the optimized structure. The substrate is on the left side of the figure. The cavity is filled by two absorbing As spacers (layers 61 and 63) white bars around a bulk GaAs active layer (layer 62, in black). The back and front Bragg mirrors are composed of alternating As (dark gray) and AlAs (light gray) layers.
