聚焦脉冲激光作用下Ge2Sb2Te5薄膜晶化过程及机理

采用聚焦脉冲激光研究了Ge₂Sb₂Te₅薄膜在沉积和激光淬火两种非晶态下反射率与激光脉冲宽度变化的关系,发现沉积态的Ge₂Sb₂Te₅薄膜在晶化触发阶段内的反射率随激光脉冲宽度增加而减小,经过激光淬火的非晶态Ge₂Sb₂Te₅薄膜在晶化触发阶段内的反射率随激光脉冲宽度增加而变化平缓.本文借用气-液体系中过饱和度分析液滴形成的原理,从统计物理学角度详细研究了两种非晶态Ge₂Sb₂Te₅薄膜在脉冲激光作用下的晶化过程及机理,结果表明,当Ge₂Sb₂Te₅的非晶态程度处于未饱和或饱和状态时不形成晶核;当Ge₂Sb₂Te₅的非晶态程度处于过饱和状态时,此时的Ge₂Sb₂Te₅为亚稳态,可能形成大小不等的晶核,但只有半径大于临界晶核尺寸时才可能长大成晶粒.而应力降低晶化能垒,增加非晶态Ge₂Sb₂Te₅的过饱和度是导致沉积态与激光淬火态的Ge₂Sb₂Te₅薄膜在晶化触发阶段内反射率随激光脉冲宽度变化规律不一致的根本原因,并据此解释了Ge₂Sb₂Te₅薄膜在这两种状态下的反射率随激光脉冲宽度的变化特点及规律.

Crystallization Mechanism and Course of the Ge2Sb2Te5 Thin Films under Focused Pulse Laser

The relationship between the reflectivity of the Ge₂Sb₂Te₅ thin films, which are as-deposited and melt-quenched states separately, and the pulsed laser time was investigated by the focused pulse laser, and it was found that the reflectivity changes for the two kinds of samples are different. On the basis of the principle of the droplet formation in the gas-liquid system and the basic ideas of the statistical physics, the crystallization mechanism and course of the Ge₂Sb₂Te₅ thin films, which are in as-deposited and melt-quenched states separately, were analyzed and studied in detail. The crystalline nucleus can’t form if Ge₂Sb₂Te₅ is in below-saturation or saturation state, different size crystalline nucleus can form if it is in super-saturation. While only the crystalline nucleus which are more than the critical size can grow into crystalline. In addition, the stress, decreasing the crystallization energy barrier and increasing the super-saturation degree of the amorphous Ge₂Sb₂Te₅, is the leading factor causing the different relationships of reflectivity change with pulsed laser width between the as-deposited and melt-quenched Ge₂Sb₂Te₅ thin films. At the same time, on the basis of the analytical results, the reflectivity change characters and laws of the two kinds of the samples under the focused pulse laser were explained in detail.