Frequency shifts of the E_2~(high) Raman mode due to residual stress in epitaxial ZnO thin films

摘要

To investigate the stress effect on the E_2~(high) Raman vibration mode, we grew heteroepitaxial ZnO films on c-plane sapphire with different strain states by changing the film thicknesses between 5 and 100 nm. To determine the relationship between the observed frequency of the E_2~(high) mode with the biaxial residual stress of the ZnO thin films, the out-of-plane strain of films were measured with x-ray diffraction from which the residual stress was calculated. The biaxial residual stress and E_2~(high) frequency were related linearly by a factor of ～170 Mpa/cm~(-1), which is in agreement with reported values from high pressure investigations of bulk ZnO.