Coupling behaviors and decoupling transitions of cdte-znte symmetric versus asymmetric double-quantum wells

The electronic structures of the (CdTe)_NW1(ZnTe) _Nab(CdTe)aN_W2-ZnTe(001) symmetric and asymmetric double-quantum wells (s-DQW and a-DQW) are presented. The tight-binding sp ³s* method, with inclusion of spin-orbit coupling, is used to calculate the band-gap energy, quantum-confinement energy, carrier planar-spin-averaged wavefunction-squared amplitudes and band structures versus the barrier thickness (N_b), well widths (N_W1 and N _W2) and valence-band offset (VBO). Special atten- tion was given to the well-to-well coupling behaviors in both a-DQW and s-DQW and the estimation of the critical barrier thickness L^crit_b corresponding to their decoupling. In the case of a-DQW, the wavefunctions of bound states are found to have strong tendency to localize in one of the two wells and, as a consequence, the decoupling occurs at L^crit_b ≃ 18 Å, much shorter than the case of s-DQW (where L^crit_b ≃ 38 Å). Our results of E_g are in excellent agreement with the available photoluminescence data and the structural and optical qualities of the experimental samples are discussed.