Precise lattice parameter measurements have been made for semi-insulating GaAs, and it is found that the lattice parameters vary greatly (order of 10-4 Å) among GaAs wafers and in a wafer. This variation of lattice parameter is closely related to the threshold voltage of the FETs, which are made by direct ion implantation on the crystal. The change of the lattice constant is probably caused by the interstitial As atoms, and a slight change of crystal growth condition may cause its variation in the wafer. Variation of the As concentration affects the threshold voltage of MESFETs when they are made by direct ion implantation.
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Takáno et al. (1985) studied this question.
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