Characterisation of hydrogen and hydrogen-related centres in crystalline silicon by magnetic-resonance spectroscopy

In recent years research by magnetic resonance has contributed substantially to the understanding of hydrogen and hydrogen-related centres in crystalline silicon. As usual for magnetic resonance, which was applied in its varieties of electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR), in several cases profound insight into the microscopic structure of centres has been the result of the studies. This includes atomic structure by identifying the chemical nature of impurity atoms and the symmetry of their geometrical arrangement within in the defect, as well as electronic structure by mapping of the defect-electron wave function. In this paper, research will be reviewed on centres which after hydrogen interaction are in a paramagnetic state. Hydrogen in its pure configuration of an isolated neutral atom on a bond-centred position in trigonal symmetry as the prototype of hydrogen centres, is described first. Shallow thermal donor centres formed at elevated temperature, similar to, but distinctly different from the more familiar oxygen-related thermal donors, are considered next. Several intrinsic lattice defects and impurities remain in a paramagnetic state, in cases when interaction with hydrogen does not lead to full passivation. Recent research on hydrogen binding on dangling bonds in mono- or multi-vacancies has resulted in the observation and understanding of several fundamental defect structures. Double donors, such as the thermal double donor and the substitutional chalcogen atoms sulphur an selenium, have been found to bind one hydrogen atom on several distinct positions remaining electrically active. Hydrogen interaction with impurities with deep electronic levels, more difficult to describe theoretically, has also been observed. In this category, transition elements from the iron, palladium and platinum groups are the examples which are considered. In an appendix the spectroscopic parameters of 32 magnetic resonance spectra with relation to hydrogen are summarised.