ABSTRACT
Silicon, the second-most abundant element on earth (a§er oxygen) having superior mechanical and electronic properties, has become the principal material of the semiconductors industry from the dawn of microelectronics, and apparently will remain dominant in the foreseen future. Silicon is a semiconductor whose electrical conductivity can be controlled over a wide range, either dynamically or permanently. Its oxidized state (SiO2) is one of the best and most stable electrical insulator and its superior chemical and mechanical properties make silicon the ideal material for advanced materials processing. For all these reasons, silicon became essentially the sole player in electronic integrated circuits, being the basic building block of most electronic devices, from transistors and diodes to microprocessors, solar cells, wireless communication devices, and more.1 Yet, silicon is not a good choice for photonic applications where optically active elements are required due to its indirect energy bandgap characteristics where energy’s minima of the conduction and the valence bands do not fall at the same wavevector (i.e., the crystal Bloch momentum normalized to ħ). ›e situation is schematically illustrated in Figure 25.1 where the energy-band diagram of silicon is shown and compared to that of GaAs, which is a direct bandgap semiconductor.
