Structural relaxation and its effects on photoluminescence properties in Si quantum wires

We calculate structural relaxation for a Si quantum wire in order to determine the mechanism of the efficient photoluminescence (PL) from Si. We find that structural relaxation, which has been ignored in most previous works, has a strong correlation to the PL properties of Si. The total energy of the quantum wire is optimized within the framework of the tight-binding (TB) approximation. The resultant structures for the ground and excited states have different band gaps, which accounts for the luminescence Stokes shift observed in experiments. We also find that the relaxation greatly improves the oscillator strength for the transition between band edges, which gives a great improvement in the luminescence efficiency.