Optical properties of Zn_1-xMn_xSe epilayers grown by molecular beam epitaxy

Zn_1-xMn_xSe (x ≤ 0.78) epilayers were grown on the GaAs (001) substrate with tilt angle 0, 3, 10, and 15 degrees toward [010] by the molecular beam epitaxy. The reflectivity, transmission, and photoluminescence experiments were used to measure the energy gap of the epilayers. A red shift of 4 meV was found as the substrate tilt angle increased from 0 to 15 degrees. The red shift in band gap energy is attributed to the increasing incoporation of smaller Zn ion with the increase in the kink density which results from the increase in the substrate tilt angle. In addition, the lattice vibration of the Zn_1-xMn_rSe (0 ≤ x ≤ 0.78) epilayers measured by the Raman scattering was found to follow the intermediate mode behavior of type 1b instead of type 1c. The force constants F_MnSe = 2.81 × 10⁶ amu·cm^-2 and F_ZnSe = 3.96 × 10⁶ amu·cm^-2 were obtained.