Surface-stress-induced optical bulk anisotropy

Using reflectance difference spectroscopy we show that Te surface terminati on 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 str ess-field in the epilayer was proven by comparing with ex situ measurents o f anisotropically stressed ZnTe layers and in situ by 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.