Study of electronic and optical properties of Zn{sub}xCd{sub}(1-x)Se

摘要

In recent years, theoretical and experimental efforts have been performed in order to understand fundamental properties of ternary alloys of II-VI semiconductors. The most promising candidates of light emitting and laser diodes in the blue-green spectral region are ZnSe-based materials. The active material in these lasers are Zn{sub}xCd{sub}(1-x)Se quantum well (QWS)[1-3]. Bulk Zn{sub}xCd{sub}(1-x)Se crystallise either in the cubic zinc-blend structure (x > 0.7), in the hexagonal wurtzite structure (x < 0.5), or in mixture of these two for 0.5 ≤ x ≤ 0.7[4]. However, growth of Zn{sub}xCd{sub}(1-x)Se on GaAs(100) substrate with molecular beam epitaxy (MBE) results in films of zinc-blend structure over the entire range of composition. Literature values for the energy gap of zinc-blend CdSe at 300k vary from 1.66 to 1.74 eV. Spectroscopic elipsometric measurements in a value of 1.74 eV[5,6] as well as a value of 1.66 eV[7]. Reflection spectroscopic[8] and photomodulation spectroscopy[9] also yield a value of 1.66 eV at 300k. The energy gap of Zn{sub}xCd{sub}(1-x)Se alloys has been determined at 300k by reflection spectroscopy[10] and spectroscopic ellipsometry[7]. To further enhance our understanding of the electronic and optical properties of Zn{sub}xCd{sub}(1-x)Se ternary material for device application, we have carried out an empirical pseudopotential band-structure calculation on this alloy.