Introduction

Abstract

In textbooks on solid-state physics, a semiconductor is usually defined rather loosely as a material with electrical resistivity lying in the range of 10⁻² − 10⁹Ω cm.1 Alternatively, it can be defined as a material whose energy gap (to be defined more precisely in Chap. 2) for electronic excitations lies between zero and about 4 electron volts (eV). Materials with zero bandgap are metals or semimetals, while those with an energy gap larger than 3 eV are more frequently known as insulators. There are exceptions to these definitions. For example, terms such as semiconducting diamond (whose energy gap is about 6 eV) and semi-insulating GaAs (with a 1.5 eV energy gap) are frequently used. GaN, which is receiving a lot of attention as optoelectronic material in the blue region, has a gap of 3.5 eV.