Electronic materials—phase diagram and crystal growth of GaAs

5 Electronic materials—phase diagram and crystal growth of GaAs 

Semiconductive elements Si and Ge (Group IVB or 13 in the periodic table) have become very important electronic materials since development of a purification method. The electronic properties of semiconductive elements of high purity can be controlled by the species and concentration of defects and impurity elements. On the other hand, in the case of semiconductive compounds, that is, III-V and II-VI compounds, we have to consider not only control of the purity of constituent elements but also the nonstoichiometry, both of which have much influence on the electronic properties. In this sense, control of the electrical properties of semiconductive compounds is more difficult than that of semiconductive elements. 

We shall now discuss the method of crystal growth and the electronic properties of GaAs, a typical example of a III-V compound which is expected to become more useful than Si and Ge in the near future, concentrating on the relation between non-stoichiometry and physical properties. GaAs has a zinc blende type structure, which can be regarded as an interpenetration of two structures with face centred cubic lattices, as shown in Fig. 3.29. Disregarding the atomic species, the structure is the same as a diamond-type 

Structure. Generally crystals with a diamond structure have covalent bonding, but crystals with the zinc blende structure exhibit ionic bonding due to the difference of electronegativity of each element. Therefore, GaAs is represented as GaLAsL 

GaAs is expected to be used for ICs (Integrated Circuit), FETs (Field Effect Transistor), LEDs (Light Emitting Diode), semiconductor lasers, and as the base material for IC. To put GaAs to practical use, the following points have to be examined in detail  

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