Crystalline semiconductors are the foundation of telecommunications, computing, and many other technologies employed in all aspects of contemporary life. Their physical characteristics are determined both by the properties of the host crystal and by the presence of impurities and crystalline defects. Control of these defects determines the commercial viability of a given new material or structure. By varying crystal growth and processing conditions, the effects of crystalline defects and impurities at surfaces, interfaces and in the bulk semiconductor can be investigated and often enhanced or eliminated.

A focus of our research is the investigation of deep-level defects in novel semiconductors and at insulator/semiconductor interfaces. Dopant impurities, which typically substitute for a host crystal atom, introduce electronic states in the bandgap close to the valence and conduction band edges and thus determine the type and conductivity of the material. These so-called shallow level defects enable the wide range of semiconductor devices available today. However, crystal lattice defects or other impurities, which introduce electronic states deeper in the bandgap and are referred to as deep level defects, also affect the properties of the semiconductor and may make a semiconductor unsuitable for its intended applications. We study the electronic properties of deep level defects using transient capacitance spectroscopy and related methods.

Another focus of our research is to control or eliminate lattice mismatch defects that degrade device properties. Semiconductor heterostructures consisting of layers of different semiconductor materials are required for many important semiconductor applications. When a semiconductor film is grown epitaxially on a substrate that has a slightly different lattice constant, the lattice mismatch strain in the film may be relaxed by the introduction of misfit dislocations or other lattice defects. Our approaqch is to modify the lattice constant at the surface of the semiconductor substrate to extend the range of materials that can be grown on it with negligible concentrations of lattice mismatch defects.

Laboratory closed, September 2015