Compound Semiconductor



Semiconductors can be elemental or compound. Group IV elements of the periodic table like germanium and silicon are examples of elemental (or) indirect band gap semiconductors. Bonding in elemental semiconductors is completely covalent. Compound semiconductors are semiconductors produced by combination of two or more elemental semiconductors, the bonding in compound semiconductors is atleast partially ionic.


Binary compounds of Group III and Group V elements like GaAs, InP and InSb (referred as III - V semiconductors) and if Group II and Group VI elements like PbS and PbTe (called II - VI semiconductors) are also semiconductors. However the ionic content in the crystal bonding is larger in the II - VI compounds. Such semiconductors are called polar (or) direct band gap semiconductors. Of these, GaAs is perhaps the most important. Its higher direct band gap of 1.4 eV and high electron mobility makes it a promising material for future high speed integrated circuits. Presently, technological problems limit the widespread use of GaAs. In I -VII compounds, the bonding is totally ionic and semiconducting properties are not observed.

Ternary and quaternary compounds of III - V and II - VI Group elements of the periodic table are also used as semiconductors. These compounds have the property that changing the composition can, to an extent, alter their band gaps. The energy gap in the Group IV elements is found to decrease with increase in atomic weight. It is true for III - V and II - VI compounds.

Some common ternary compound semiconductors are listed in Table 1

 
 
 
 

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