Band structure calculations of Ga_{1 - x}Al_xAs, GaAs_{1 - x}P_x and AlAs under pressure

The band structure of Ga_{1 - x}Al_xAs and GaAs_{1 - x}P_x cation and anion alloys respectively are calculated within the virtual crystal approximation using an adjusted empirical pseudopotential scheme, which incorporates compositional disorder as an effective potential. It is shown that the present theory, which is free from any additional parameter, satisfactorily produces the band-gap bowings. The effect of alloying was correlated to the effect of positive and negative pressure in AlAs. We have also calculated the variation of the ionicity of these alloys under pressure, the results are linked to the high pressure phase transitions.