Ab initio studies of the Si1−xGex alloy and its intrinsic defects

We have performed systematical ab initio studies of the electronic and structural properties of the disordered phase of the Si1−xGex alloy. For the defect free alloy, we find that the Si–Si bond length has a tendency to maintain its natural value (x=0) all the way up to x>0.5, similarly to what is found experimentally. We also analyze the vacancy, and note, as expected for a structurally as well as chemically disordered solid, that there is no local symmetry around the vacancy site. Finally, we perform some studies of the alloy under pressure all the way up to 30 GPa, and find that the structure is highly distorted in some cases, indicating that an amorphous phase may be found in the pressure region of the diamond–β-tin phase transition.