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

We have performed systematical ab initio studies of the electronic and stru ctural properties of the disordered phase of the Si1-xGex alloy. For the de fect free alloy, we find that the Si-Si bond length has a tendency to maint ain 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 n o 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 str ucture is highly distorted in some cases. indicating that an amorphous phas e may be found in the pressure region of the diamond-beta -tin phase transi tion. (C) 2001 Elsevier Science B.V. All rights reserved.