Fine tuning of the emission of ultra-thin quantum wells of CdSe and CdTe by modification of the growth temperature

Ultra-thin quantum wells (UTQWs) of CdTe and CdSe should present a emission energy as a function of thickness, however, we have observed that depending on substrate temperature the peak energy is modified: the higher the growth temperature the larger the blue shift. Considering (i) a chemical interaction that produces the substitution of Cd atoms by Zn atoms at the QW-barrier interface, and, (ii) the large Bohr radius of the excitons in II-VI semiconductors, we argue that a few percent substitution of Cd atoms by Zn atoms is perceived as a change in average composition and not as a thickness fluctuation. Since the Cd substitution is a thermally activated process, a larger blue shift is expected at the higher temperatures. Therefore, the UTQWs can be described as made of Zn_1-xCd_xSe or Zn _1-xCd_xTe alloys with high Cd content, x∼1 at the lower substrate temperatures (T_s). Then, the proper selection of T _s can be advantageously employed for fine tuning of the excitonic emission in the energy region between that of UTQWs of the pure binary compound with thickness difference of 1 ML, making possible to cover continuously the visible spectral region with CdTe and CdSe UTQWs.