Dipolar interactions between unpaired Si bonds at the (111)Si/SiO2 interface

An electron spin resonance (ESR) study has been carried out on the P-b cent ers (interfacial Si-. drop Si-3) in standard thermal (111)Si/SiO2, of which , in the as-grown state, a density 4.9 x 10(12) cm(-2) is inherently incorp orated. The P-b density was significantly enhanced to various levels throug h post oxidation annealing in H-2 ambient at elevated temperatures. This re sulted in the observation of distinct P-b density-dependent magnetic field angle anisotropy in the ESR spectra, herewith definitely establishing the i mportance of the magnetic dipolar interactions within the two-dimensional P -b defect system. Field angle dependence of dipolar origin is observed in l inewidth, line shape, and resonance position. The data are interpreted with in the framework of a computational model based on the magnetostatic approx imation of the local magnetic field, which resulted in a detailed analysis of the line broadening mechanisms. The successful simulation provides evide nce for P-b density-dependent variations in the strain broadening contribut ion, indicating a growing relaxation of the interfacial strain with increas ing P-b density. Additionally, the spatial P-b defect distribution is found to exhibit a self-avoiding behavior, with apparently no P-b pairs occurrin g within third nearest-neighbor distance. These results are interpreted wit hin a picture connecting defect generation with relaxation of interfacial s train. Magnetic susceptibility measurements reveal an almost purely Curie-t ype behavior of the P-b system with Curie temperature T-c < 1.3 +/- 0.8 K.