Reversible Ordering of a-Si1-xGex by the Combined Effect of Light and Temperature

Amorphous Si and a-Si1-xGex (0 ≤= x ≤= 0.38) films illuminated by above bandgap light, and heated between 110 and 180°C, undergoes an ordering transition, which is reversed to the amorphous phase by either heating up above 180°C or cooling down below 110°C. This structural change is investigated by Raman spectroscopy. The changes observed in the Raman spectra reveal the formation of small ordered clusters (only a few lattice parameters in diameter). The ordered state was not observed by the only effect of either light or temperature, suggesting that specific temperature and light excitation conditions are necessary to generate and support the ordered state, that appears as a nano-crystalline structure.