The enhancement of hyper Raman effect from semiconductor surfaces

The convenient experimental technique for studying surface or interface reg ions in semiconductors is the Hyper Raman Scattering (HRS). The effect of t he band bending near the surface of a semiconductor results often in the ac cumulation of free carriers near the surface. The electronic contribution t o the dielectric function epsilon(z) is negative in this region. Varying fr om a negative value in the surface overlayer up to a positive value in vacu um, epsilon(z) vanishes in some planes. According to Maxwell's equations, t he electric field of both incident and scattered waves becomes infinite in the surface area. The infinity is cut by the electronic collisions from imp urities or by the spatial dispersion. Nevertheless, there remains a finite enhancement of HRS intensity (the enhancement factor is 100 to 1000). An ex ample of semiconductor-metal interface is discussed.