Effects of pressure and composition on the gap properties of AlxGa1-xA
s randomly disordered alloys are investigated theoretically and experi
mentally. The analogy between pressure and alloying effects is explore
d. Special attention is given to the direct-to-indirect gap transition
region, where the gap sensitivity to both pressure and composition va
riations is shown to be strongly enhanced. A 30% decrease in luminesce
nce 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 s
everal tens of kbar. Calculations are performed within the small cryst
al 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.