Studies of Spectroscopic Ellipsometry in Cd_1-xMn_xTe/CdTe Superlattices

Cd_1-xMn_xTe/CdTe superlattices and thin films were grown by molecular beam epitaxy on GaAs (001) substrates. Spectroscopic ellipsometry measurements were performed on Cd_1-xMn_xTe/CdTe superlattices with compositions x=0.4, 0.8, and Cd_1-xMn_x thin films with x=0.2, 0.4, 0.6 at room temperature in the photon energy range 1.4--5eV. In superlattices the pseudodielectric functions measured by ellipsometry show specific features related to the exciton transition between quantized interbands. The exciton transitions related to the heavy holes of 11H, 22H, and 33H are observed and identified. In thin films spectroscopic ellipsometry allows the clear identification of the energy gap E₀. Additionally, critical point transitions are observable in both the spectra of the superlattices and films. Photoreflectance spectra were also performed at room temperature in order to compare with our ellipsometry results. After taking into account the strain-induced and quantum confinement effects, the theoretical calculations are in good agreement with our experimental spectra. Ellipsometry appears to be a suited technique to monitor the MBE growth, ultimately also in situ, of diluted magnetic low-dimensional systems.