Transition behaviors from coupled-to-uncoupled CdTe - ZnTe symmetric versus asymmetric double quantum wells

The coupling behaviors between symmetric versus asymmetric CdTe - ZnTe double quantum wells (DQWs) are theoretically investigated based on the application of the sp³ s^* tight-binding method including the spin-orbit interaction. This method is used to calculate the band structures of the (CdTe)_Nw ₁ (ZnTe)_Nb (CdTe)_Nw 2=₂ - ZnTe DQWs versus the barrier thickness (N_b), and well widths (N_{w 1} and N_{w 2}). Special attention was given to the decoupling behaviors between the wells in both symmetric and asymmetric cases. The decoupling of the asymmetric DQWs is found to occur at a critical barrier thickness (of about L_b^crit ≃ 18 over(A, ̊)) shorter than the case of symmetric DQWs (of about L_b^crit ≃ 38 over(A, ̊)) because, in the former case, the bound state wavefunctions have more tendency to localize in one of the two wells. Our modelling of asymmetric DQWs (with N_w1 = 6 and N_w2 = 3) yields results in excellent agreement with the available experimental photoluminescence data.