We have investigated the electronic properties of AlAs/Si(Ge)/GaAs and GaAs
/Si(Ge)/AlAs (001) interfaces, employing first-principles total-energy calc
ulations. Our results reveal that the decrease or increase of the valence-b
and offset can be attributed to the segregation of Si or Ge atoms toward Al
As or GaAs layers. The segregation gives rise to an asymmetrical distributi
on of Si or Ge atoms at the AlAs/GaAs interface. [S0163-1829(99)01320-X].