Fig. 6.

Schematic of the energy processes occurring following optical excitation (left) as a function of the radial position and (right) as a function of time. The direct transitions are shown with solid vertical lines, and the indirect transitions are shown with dashed lines. The optical excitation of carriers into the barrier is followed by rapid (picosecond) scattering, both directly into the confined states in the well and into the X-valley in the barrier. This excitation is followed by slow (nanosecond) electron scattering into the well from the X-valley of the barrier, which is near isoenergetic with the X-valley energy. Direct carrier recombination from the X to the HH band is suppressed. In the case of high excitation density, the electron states in the well will become filled, and electrons will remain stored in the barrier X-valley