Optical properties of Zn1−xCdxSe-ZnSe superlattices grown by metal organic vapour phase epitaxy

An investigation of the reflectivity and photoluminescence spectra of 40-period Zn1−xCdxSe-ZnSe strained layer superlattices is reported. Superlattices with cadmium composition between 3% and 10% were grown by metal organic vapour phase epitaxy. The well and barrier widths were varied in order to study the tunnelling effect in the superlattices. This effect was shown to be large not only for the excited states (e2hh2 transitions for the 10% cadmium composition) but also for e1hh1 transitions despite the large heavy hole effective mass. The band discontinuities were determined by calculating the transition energies within the envelope function framework generalized to strained layers. It was found that for all superlattices the mechanical state is pseudomorphic and that the heavy hole band offset is 32% of the energy difference of the strained band gaps. The binding energies and the oscillator strengths of the various excitonic transitions were calculated within the formalism of fractional-dimensional space and compared with variational calculations reported in the literature.