Lattice Defects and the Electronic Properties of Semiconducting Materials

A perfect crystal described as an entity that has perfect translation, reflection, or rotation symmetry does not exist in nature, and even if it existed would not have any useful property. Nearly all the numerous attributes of a crystalline material, from its mechanical, electrical, optical and other properties, depend on the existence of lattice imperfections. In this talk we consider the influence of a particular type of lattice imperfection, namely line defects, on the electronic properties of a particular wide band gap semiconductor, SiC. This is one of the new generation of semiconductors which is currently the focus of much interest because electronic devices fabricated from SiC have novel applications at high temperatures or in environments where elevated temperature or radiation destroys devices made from conventional semiconductors, such as Si or GaAs. We consider bipolar SiC devices such as PiN diodes that enable higher blocking voltages at lower on-state resistances in comparison with silicon based devices. It has been found that under forward biasing, SiC bipolar devices rapidly degrade and this has so far hindered the development and commercialization of SiC electrical devices. We show how dislocations that extend from the substrate into the active regions of device during epitaxial growth are the primary culprits in the degradation of SiC bipolar devices. In particular, stacking faults that nucleate at basal plane dislocations rapidly expand by the phenomenon of recombination-induced glide (REDG) leading to an increase in the forward voltage drop that renders the device unsuitable for commercial applications. The structural details of onedimensional lattice defects in SiC, the driving force for their nucleation and propagation, the intricacies of REDG, and the steps that can be taken to minimize these effects will be discussed. The hope is that this example will show how the materials properties of various semiconductors, from elemental ones like silicon and germanium, to compound semiconductors like GaAs, SiC and GaN, play a predominant role in how a device behaves in real world and the role of material scientists in solving these problems.