Dr Neil Curson – Single donors in silicon studied with scanning tunnelling microscopy
As integrated circuits shrink to the nanoscale and silicon-based quantum information technologies develop, the role played by donors in silicon becomes ever more critical. Tremendous advances have recently been made in the study and manipulation of donors in GaAs [Lee & Gupta, Science 2010] and the measurement of the quantum properties of ensembles of Group V donors in silicon [Greenland et al., Nature (2010)]. At the London Centre for Nanotechnology we and collaborators have undertaken a initiative called Coherent Optical and Microwave Physics for Atomic-Scale Spintronics in Silicon (COMPASSS), to control and manipulate the Rydberg states of Group IV donors for quantum information processing applications. The goal of the STM group is to establish a comprehensive knowledge of how donors in silicon interact with their environment and with each other, and how these interactions can be manipulated, at the atomic-scale. Recently we have studied individual Group V donors in silicon, spectroscopically, using STM. We find that at the Si(111)2×1 surface of cleaved silicon, the structural and electronic properties of Group V donors depend critically on their atomic mass and the substitutional site they occupy. Surprisingly it is possible for the same donor to induce either a positive or negative local charge state in the surface. This phenomena results from the donor occupation of non-equivalent sites in the surface, is explained by an electron counting argument and is subtly different from that of other charging effects seen on Si and GaAs surfaces.