Thermal Strain of In films deposited onto Si and GaAs Substrates

研究了在300K和77K温度下沉积在Si和GaAs衬底上的In薄膜的热应变，然后冷却到20K。用X射线衍射法测量了In、Si和GaAs热膨胀不同引起的In应变。此外，20K时的应变大小与利用双轴应变模型计算的热膨胀系数的差值相近。对于In薄膜，计算中同时考虑了热膨胀系数和杨氏模数的各向异性。在真空度为10^&lt；-7&gt；-^&lt；-6&gt；时，In薄膜表面形貌由岛状结构转变为连续结构。在真空室中进行In的预蒸发后，得到连续的薄膜。因此，薄膜形貌的变化似乎是由真空室中的氧气浓度引起的。In膜的厚度为100~140 nm。由于In薄膜的热膨胀系数大于Si和GaAs衬底的热膨胀系数，在室温至20K的温度范围内，薄膜在垂直方向上会产生压缩应变。测量和计算的应变值与晶体取向有很强的相关性。(001)取向的大应变为-1.0%，(111)、(001)和(313)取向的小应变为-0.6%。实验测得的应变值对晶向的依赖关系与计算的应变值很好地吻合。虽然薄膜厚度越小，薄膜越连续，应变值越大，但实际应变值仅为计算应变值的-70%。这意味着薄膜发生了塑性变形的松弛。

An investigation has been carried out of the thermal strain in In films deposited onto Si and GaAs substrates at 300k and 77k and then cooled down to temperatures as low as 20k. The strain in the In caused by differences in thermal expansion of In, and Si and GaAs was measured using X-ray diffraction techniques. Also the magnitude of the strain at 20k was found to approximate the strain value calculated from the difference in the thermal expansion coefficients using the biaxial strain model. For the In films, the crystallographic anisotropy both of the thermal expansion coefficient and Young's modulus was considered in calculations. The surface morphologies of In films evaporated in a vacuum of 10^<-7>-^<-6>were changed from island to continuous structures. The continuous films were obtained after that pre-evaporation of In was carried out in a vacuum chamber. Therefore, the change of film morphologies appeared to be caused by the oxygen concentration in the vacuum chamber. The thicknesses if In films were 100 to 140 nm. Since the thermal expansion coefficient of In film was greater than that of Si and GaAs substrates, compressive strain in the vertical direction of film was occurred according as the temperature was down room temperature to 20k. The measured and calculated strain values have a strong dependence on the crystal orientations. A large strain of -1.0%was obtained for (001) oriented grain and small strains of -0.6%were (111), (001) and (313) oriented grains. The dependence on the grain orientation of measured strain values was well agree with calculated strain values. Although the measured strain value were increased as the thickness of films decreased and films were more continuous, the measured strain values merely reached to -70%of the strain values expected by calculation. This mean that the film occurred the relaxation by plastic deformations.