EXCITONS AND MULTI-EXCITON COMPLEXES BOUND TO A 2-DIMENSIONAL HOLE LAYER AT A SILICON SURFACE - THE KONDO EFFECT, THE COULOMB-BLOCKADE AND A NEGATIVE PHOTOCONDUCTIVITY

The recombination radiation Line of surface excitons and the recombina tion radiation line of multi-exciton complexes bound to a two-dimensio nal hole layer are observed in luminescence spectra of [100] silicon m etal-oxide-semiconductor structures at low two-dimensional hole densit y. The circular polarization of these two lines in a transverse magnet ic field is defined by the average electron spin. The hole spin contri bution to the circular polarization is very small due to Kondo spin co rrelations of holes in the excitons and complexes and holes in the two -dimensional hole layer. The Coulomb blockade excludes a direct contri bution of the complexes to a surface photoconductivity. Moreover, a si gnificant negative photoconductivity of the two-dimensional holes is o bserved at high excitation levels, presumably as a result of the quant um scattering of the two-dimensional holes by the complexes. A shell m odel of surface multi-exciton complexes is introduced. (C) 1998 Academ ic Press Limited.