A FIELD-IONIZATION MECHANISM FOR A HIGH REFRACTIVE NONLINEARITY IN HEAVILY-DOPED N-GAAS

A new microscopic model is proposed to account for the strong and fast refractive index nonlinearity recently found in heavily doped n-GaAs. The model involves tunneling ionization of the donors induced by the space-charge field generated by the nonhomogeneous light intensity pat tern. In particular, negative refractive index changes DELTAn = -5 x 1 0(3) for excitation pulses of 5 x 10(5) W/cm2 at 885 nm can be reasona bly explained. Response times are estimated to be in the sub-nanosecon d regime (10-100 ps).