矽(Si)基板與砷化鎵(GaAs)薄膜所構成的層狀異質結構，可以結合電子與光學元件的優點於單一系統內，但採用這種異質結構會間接導致元件內部產生大量缺陷，嚴重影響薄膜的品質與光電性能，因此元件中薄膜之機械性質量測顯得格外重要。本文即利用分子動力學(Molecular Dynamics, MD)模擬GaAs/Si結構之奈米壓痕(Nanoindentation)機制，藉以了解GaAs薄膜之機械特性。
經過模擬分析之後，發現GaAs薄膜之硬度與楊氏係數會隨著薄膜厚度的增加而降低；隨著壓痕深度的加深而變大，意即基板效應會隨著薄膜厚度增加而減小；隨著壓痕深度加深而變大，估計薄膜厚度須達奈米壓痕深度的10倍以上才能消除基板效應，隨後本文利用King的理論求得較接近薄膜真實的楊氏係數。而壓痕過程中薄膜由彈性變形轉變成塑性變形的Pop-in現象，在力量位移曲線中均能清楚的呈現出來。此外本文也在兩材料的介面處發現部分因差排而導致的滑移線，呈現出與現實相同的物理現象。

The layered heterostructure constructed by Si substrate and GaAs film can combine the benefits of electronic and optical components in one unit. But this heterostructure produces a large number of defects within the component indirectly. These defects often reduce the quality and optoelectronic efficiency of GaAs film seriously. So the measurement of GaAs film’s mechanical properties plays an important rule. This paper investigates the deformation and phase transformation behavior of GaAs/Si layered heterostructures under nanoindentation by using Molecular Dynamics (MD) to discuss the mechanical properties of GaAs film.
After the analysis, we can obtain that the hardness and Young’s modulus of GaAs film decrease with the thickness of GaAs film and increase with the indentation-depth. In other words, the effect of substrate decreases with the thickness of GaAs film and increases with the indentation-depth. We conclude that the effect of substrate will be reduced when the thickness of GaAs film becomes ten times greater than the indentation-depth. Then we introduce King’s analysis to estimate the true Young’s modulus of GaAs film and finally obtain approximate results. Besides, during indentation process, the force-displacement curve reveals the pop-in event clearly which corresponds to the elastic-to-plastic transition within GaAs film. Furthermore, we are able to observe dozens of slip lines caused by dislocation near the material interface which is familiar to the physic phenomena in the real case.

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