SI-C ATOMIC BOND AND ELECTRONIC BAND-STRUCTURE OF A CUBIC SI1-YCY ALLOY

We apply the sp(3)s tight-binding model to study the electronic energ y band structure of the cubic Si1-yCy alloy. First by the effective me dium approximation where local atomic fine structures are averaged out , it is obtained that the energy band gaps of both relaxed and straine d Si1-yCy alloys increase with increasing C content. The effect of the local Si-C atomic bond structure on the energy band is studied in the real space in order to include the actual broken translational symmet ry in the Si1-yCy alloy. The electronic local densities of states are investigated and the following is concluded: (a) When Si-C bond length in the alloy assumes the crystal SiC one (strained alloy), an electro nic state at the C atom and its surrounding Si atoms is induced in the energy band gap of crystal Si. The valence I,and edge is slightly lif ted. The results indicate a type I energy band alignment for strained Si1-yCy/Si quantum well. (b) When the Si-C bonds assume the Si-Si bond length of the crystal Si (relaxed alloy), the electronic states are n ot much modified. [S0163-1829(98)07535-3].