Substitution Gallium Arsenide, GaAs

1When it is necessary to emphasize the variable composition aspects of a phase, the formula will be preceded by 

There are a number of ways this stoichiometry change can come about. Additional As atoms might be incorporated from the vapor and added to the crystal surface at both As and Ga sites  

This would produce a crystal with a formula (Gaj xAsx/2jAsj /2, where the atoms occupying Ga sites are enclosed in parentheses. This model indicates that there are vacancies on both the Ga and As sublattices in the crystal. 

These point defect models need to be regarded as a first approximation. Calculations for stoichiometric GaAs suggest that balanced populations of vacancies on both gallium and arsenic sites, VGa and VAs, exist, as well as defect complexes. Calculation for nonstoichiometric materials would undoubtedly throw further light on the most probable defect populations present. 

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