Defect clustering in silicon emitter junctions

Process induced defect centers in highly doped n++-p+ junctions with phosphorus and gallium or boron diffusion profiles have been investigated. The emission properties of the generation centers in these types of emitter junctions have been studied for the first time by using a specially designed method based on Deep Level Transient Spectroscopy. The emission of charge carriers from defect electron states and hole states in the space charge region of the p-n junctions is shown to consist of thermal and tunneling processes. The latter component is more pronounced for higher concentrations of shallow dopants in the p-n junction and can be explained only by assuming the presence of local electric fields to be much higher than the average fields in the space-charge regions. The emission of charge carriers is localized to the n++ region and has the same properties for p-type profiles of gallium and boron. We conclude that the creation of defects, giving rise to increased local electric fields in the emitter junctions, is determined by a clustering process related to the concentration of phosphorus.