Elemental and Compound Semiconductors

Elemental semiconductor are crystals where each point of the lattice is occupied by an atom of a single element, such as Si or Ge. The atoms are bound together covalent forces, where each atom shares an electron with its nearest neighbour forming strong bonds. Compound semiconductors consist of more than one element in the crystal structure occupying the lattice sites. Common examples are GaAs or InP. The example compound semiconductors belong to the III-V semiconductors so called because first and second elements can be found in group III and group V of the periodic table respectively. In compound semiconductors, the difference in electro-negativity leads to a combination of covalent and ionic bounding. Ternary semiconductors are formed by the adition of a small quantity of a third element to the mixture, for example GaAl_xAs_1-x. The subscript x refers to the alloy content of the material, what proportion of the material is added and what proportion is replace by the alloy material. The addition of alloys to semiconductors can be extended to include quaternary materials such as Ga_xIn_yAs_(1-x)P_(1-y) or GaInNAs and even quinternary materials and even quinternary materials Again, the subscripts denote the amount of doping in the material. Alloying semiconductors to form these compounds allows the bandstructure and lattice spacing of the material to be altered.