Spin-orbit splitting and critical point energy at Γ and L points of cubic CdTe nanoparticles: Effect of size and nonspherical shape

This study reports the observation of changes in critical point energy at Γ and L points and an increase in spin-orbit splitting energy of cubic CdTe nanoparticles in comparison to the bulk single-crystal value. ε₁ and ε₂ spectra of CdTe nanoparticles, accurately derived from spectroscopic ellipsometry measurements on CdTe nanoparticles dispersed in SiO₂ films, show E₀, E₀+Δ₀, E₁, and E₁+Δ₁ critical points at 1.75, 2.74, 3.29, and 3.83 eV, respectively. Glancing-angle x-ray diffraction and high-resolution transmission electron microscopy investigations confirm cubic CdTe nanoparticles with good crystallinity and a nonspherical shape. Variable magnitudes of size-induced stress along the minor and major axes cause dissimilar shifts of heavy-hole and split-off bands resulting in a positive contribution to spin-orbit splitting energy, in addition to the small size.