Microscopic calculation of second-harmonic generation at semiconductor surfaces: As/Si(111) as a test case

We outline a method to determine the intensity of the second-harmonic radiation emitted from a semiconductor surface. A calculation carried out for As/Si(111) allows us to discuss details of the nonlinear response such as the relative contributions of transitions resonating at the incident or at the emitted frequency. We also show that second-harmonic generation can be used as a tool for surface spectroscopy. We also show that the intensity of the emitted radiation, rather than the nonlinear susceptibility, should be compared with experiment, since the intensity is less sensitive to computational details than the second-order susceptibility.