Defect Engineering for Controlling Semiconductor Diffusion

128 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2005.Bulk point defects such as vacancies and interstitial atoms govern many aspects of the behavior of crystalline solids, especially for semiconductors. Essentially no literature has focused upon bulk point defects as the mediators of the physics of surface-bulk coupling, however. We have discovered two distinct mechanisms by which surfaces influence formation and annihilation rates of bulk point defects. In the first mechanism, surfaces can couple to the semiconductor bulk through electrostatic interaction with charged defects. Such coupling manifests itself in the form of a near-surface electric field that halts the motion of charged defects toward the surface and results in increased diffusion. The second mechanism involves direct creation and generation of defects at the surface bonds. We show through self-diffusion measurements in silicon that defect concentrations deep in the semiconductor bulk can be varied controllably over several orders of magnitude through submonolayer-level adsorption at the surface. For example, decreasing amount of nitrogen adsorbed on silicon that is undersaturated in defects raises their concentration and speeds diffusion, with the effects extending at least 0.5mum into the bulk. Similar adsorption on supersaturated silicon lowers the defect concentration and inhibits diffusion. These phenomena open the possibility of precise defect engineering for numerous applications such as transistor fabrication, optoelectronics, photocatalysis, and hydrogen production by water splitting.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD