Chapter 6 - Ab-initio modeling of defects in germanium

Abstract

This chapter reviews the ab-initio modeling activities and outlines the differences between first-principles quantum mechanical methods and more approximate techniques. Several simulated results are compared with experimental data to validate the potential of the simulation techniques. The chapter describes the problems and successes in applying density functional methods to defects in Ge. The very large error in the band gap found from using local density functional theory (DFT) can create problems. For example, if a defect possesses an electrical level in the band gap and the structure depends on the charge state, then a supercell approach is unlikely to capture the structural change on charging the defect. This can be overcome but only at the expense of using a method that produces a realistic band gap. One simple approach may be in using hydrogen terminated clusters as these lead to a substantial band gap. \\