Thermal Strain of In films deposited onto Si and GaAs Substrates

本文研究了在300 K和77 K温度下淀积在Si和GaAs衬底上的In薄膜，然后冷却到20 K时的热应变。使用X射线衍射技术测量由In、Si和GaAs的热膨胀差异引起的In中的应变。此外，发现在20 K下的应变的大小近似于使用双轴应变模型从热膨胀系数的差异计算的应变值。对于In薄膜，计算中考虑了热膨胀系数和杨氏模量的晶体学各向异性。真空度为10^ -^时，In薄膜的表面形貌<-7><-6>由岛状结构转变为连续结构。在真空室中进行In的预蒸发之后获得连续膜。因此，薄膜形貌的变化似乎是由真空室中的氧浓度引起的。In膜的厚度为100至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，当温度从室温降至20 K时，薄膜在垂直方向上发生压应变。测量和计算的应变值有很强的晶体取向的依赖性。（001）取向晶粒的大应变为-1.0%，（111）、（001）和（313）取向晶粒的小应变为-0.6%。测量的应变值与计算的应变值的晶粒取向的依赖性是一致的。虽然应变测量值随薄膜厚度的减小和薄膜连续性的提高而增大，但测量值仅为计算值的-70%。这意味着薄膜发生了塑性变形松弛。

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.