Optical characterization of intersubband transitions in Zn_xCd_1-xSe/Zn_x^′Cd_y^′Mg_{1-x^′-y^′}Se multiple quantum well structures by contactless electroreflectance

Contactless electroreflectance was measured at room temperature to characterize a wide range of the possible optical transitions in Zn_xCd_1-xSe/Zn_x^′Cd_y^′Mg_{1-x^′-y^′}Se multi-quantum-well structures grown by molecular beam epitaxy. Based on these measurements, the authors predict and then verify the anticipated intersubband transition energies. They investigate a representative Zn_0.5Cd_0.5Se/Zn_0.20Cd_0.19Mg_0.61Se structure, for which the E1-E2 transition energy is predicted to be 178 meV (6.97 μm). Intersubband absorption using Fourier transform infrared spectroscopy exhibits a peak at 180 meV (6.89 μm), in excellent agreement with the contactless electroreflectance measurements.