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Effects of pressure and composition on the gap properties of AlxGa1−xAs randomly disordered alloys are investigated theoretically and experimentally. The analogy between pressure and alloying effects is explored. Special attention is given to the direct-to-indirect gap transition region, where the gap sensitivity to both pressure and composition variations is shown to be strongly enhanced. A 30% decrease in luminescence intensity is produced on a x=0.46 sample under applied pressure of 0.7 kbar, while a similar effect in GaAs would require pressures of several tens of kbar. Calculations are performed within the small crystal approach using 64-, 216-, and 1000-atoms basic cluster sizes, with periodic boundary conditions. Convergence of the calculated properties with the cluster size is discussed.

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