Surface-stress-induced optical bulk anisotropy

Using reflectance difference spectroscopy we show that Te surface termination on ZnTe induces, due to stress occurring from dimerization and the piezo-optic effect a dichroism at the $E_1$ and $E_1+{\Delta }_1$ critical points of the dielectric function of the ZnTe. The influence of Te dimers on the stress-field in the epilayer was proven by comparing with ex situmeasurents of anisotropically stressed ZnTe layers and in situby enhancing the stress effect by inserting one atomic plane of Cd. Under Zn termination no stress-induced anisotropy occurs. A recently developed theoretical model describes our measured data well in terms of lifting of degeneracy of the $E_1$ and $E_1+{\Delta }_1$ transitions by anisotropic stress along the Te dimer direction.