Effects of Si addition on the crystallization behaviour of GeTe phase change materials

The effects of the addition of Si on the temperature dependence of the electrical resistance and crystallization temperature, Tx, of GeTe films were investigated by a two-point probe measurement. Tx of the (GeTe)100-xSix films increased with increasing Si content from x = 0 (188 °C) to x = 12.6 at% (297 °C). It was confirmed from XPS measurements that Si-Te bonds were formed in the (GeTe)100-xSix amorphous film by the addition of Si. The dependence of Si content on the Tx of the (GeTe)100-xSix film was calculated based on Lankhorst's model, which showed a linear relationship between Tx and the Si content. In the region of low Si content (x ⩽ 3.8 at%), the obtained result was in good agreement with the calculated result. Meanwhile, in the region of high Si content (x ⩾ 5.4 at%), the obtained result considerably deviated from the calculated line. This may be due to the formation of the strongest Si-Si bonds in the amorphous (GeTe)100-xSix film. It was found from XRD measurement that the (GeTe)87.4Si12.6 amorphous film showed crystallization with phase separation into α-GeTe and Si. The obtained results suggested that suitable Si content of the (GeTe)100-xSix film is in the range 3-7 at% because of the high Tx, a small temperature interval of crystallization and the absence of phase separation during crystallization.