ABSTRACT
The ATQW sample was grown by molecular beam epitaxy (MBE) on a semi-insulating (001)
GaAs substrate. Three nominally undoped GaAs quantum wells, with widths of 7.6, 8 .8 and 10.8 nm were separated each other by undoped 2-nm-thick Alo.3Gao.7As barrier layers and embedded between 100-nm-thick Alo.3Gao.7As cladding layers. The barrier layers were so thin that the electrons could easily transfer between the three wells by tunneling transitions. The tunneling transfer of the electrons is faster than that of the holes because of the smaller effective mass of the electrons. The well widths had been designed so that three electronic states would be resonant by a small external electric field [7]. The schematic QW structure is shown as the inset of Fig. 1. To measure the optical transmission change of the ATQW, the GaAs substrate and 5 nm GaAs capping layer were removed partly by selective wet chemical etching.
