Electrodynamical enhancement of Hyper Raman Scattering from boundary and surface areas in semiconductors

In semiconductors near surfaces or boundaries with other materials there ex ist dielectrically inhomogeneous macroscopic areas caused by energy bands b ending. The electron density depends on the depth in such regions, n = n(z) , and so does the dielectric permittivity epsilon(omega,z). The density can be so large (accumulation overlayer) that the dielectric permittivity beco mes negative. The permittivity epsilon(omega,z) changes gradually from posi tive values at one boundary of the overlayer to negative values at the oppo site side assuming zero value in between. Maxwell's equations yield the res ult that the normal component of the electric field of the incident light i s inversely proportional to epsilon(omega, z) and it tends to infinity when epsilon(omega, z) = 0. If we take into account weak electronic collisions and/or spatial dispersion, the infinity is suppressed and the enhancement o f the field remains strong but finite. Hyper Raman Scattering (HRS) which i s caused by the enhanced electric field of the incident light is shown to b e enhanced too. Two kinds of the overlayers are considered: the surface; re gion of heavily doped semiconductor and the space charge region at the meta l-semiconductor contact. The enhancement of the HRS intensity reaches 10(3) .