Strain dependence of second-harmonic generation in silicon

Strained silicon is a versatile new type of material, which has found application in microelectronics and integrated optics. The applied strain alters the electronic and optical properties and gives rise to new properties previously not known to exist in silicon, like a bulk second order nonlinear susceptibility. Here, we determine experimentally the strain dependence of the second order nonlinear susceptibility on the applied strain. To this purpose, the strain induced second harmonic signal generated in the silicon was measured in a reflection geometry with azimuthal angle dependence. The extracted components of the second order nonlinear susceptibility were determined and compared to the unstrained case. Additionally the measurements were compared to results obtained with an analytical model, that takes into account the exponential strain decay at the sample surface. The predicted linear dependence between the surface strain and the second order nonlinear susceptibil ity agrees well with the results of our experimental work.