Large electro-optic effect in tensile strained Ge-on-Si films

The authors report the first observation of a large, strain-enhanced, electro-optic effect in the weakly absorbing regime for Ge epitaxial films grown directly on Si substrates. The field dependence of absorption in the Ge films was measured from spectral responsivity measurements of Ge-on-Si p-i-n diodes. The experimental data were analyzed using the generalized Franz-Keldysh formalism [H. Shen and F. H. Pollak, Phys. Ref. B 42, 7097 (1990)] and the valence band edge shifts of the light- and heavy-hole energy positions were in response to biaxial stress. With measured Delta alpha/alpha similar to 3 and derived Delta n/F=280 pm/V, the material has significant potential for field-induced phase or electroabsorption modulator devices. (c) 2006 American Institute of Physics.