Electronic properties of defects in semiconductors
Lattice mismatched semiconductor structures
Deep level transient spectroscopy (DLTS)
High resolution x-ray diffraction and x-ray microdiffraction
The focus of our research is the study of semiconductor defects. Our goal is to understand how defects originate, their atomic configuration, and their effects on the properties of the material. New semiconductors and new device structures have defects with a wide variety of physical properties. Understanding these defects will lead to improved semiconductor devices for applications in communications, computation and technology.
The physical characteristics of semiconductors are determined both by the properties of the host crystal and by the presence impurities and crystalline defects. 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 modify the properties of the semiconductor and thus may make a semiconductor unsuitable for its intended applications.
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. The electronic and optoelectronic devices for many important semiconductor applications are complex engineered structures in which both the lattice mismatch strain and the defects must be tightly controlled.