Thermal Stress Distribution For GaAs Directly Grown On Patterned Silicon

With the rapid development of information technology,the world has been brought into a comprehensive information society,and will become an information economy society.From top to a country down to an enterprise or an individual,it is not only the material wealth,but also the information resources and the speed of obtaining information,according to which to measure its competitive strength.The construction of"information expressway" can't be separated from the development of optical communications,and Si based optoelectronic integration is one of the key step.As a carrier,the Si substrate is undoubtedly advantageous due to its good thermal conductivity,low cost,maximum wafer diameter and mature technology.On the other hand,the ?-? compounds,primarily gallium arsenide,are the basic optoelectronics materials and due to considerably higher carrier mobility form the basis for high-speed special-purpose devices.Therefore,how to integrate the Si substrate and GaAs-based optical devices better has attracted the attention of many researchers.However,the epitaxial growth of GaAs on Si substrates is still facing the challenges of lattice mismatch,thermal mismatch and polarity mismatch,and the resulting defects could greatly degrade the electrical and optical properties of GaAs.Based on the GaAs/Si epitaxial growth,our laboratory found that using the patterned substrate can reduce the thermal stress of the epitaxial layer and effectively block the dislocations in the GaAs epitaxial layer to obtain a high-quality GaAs film.While measurable and experiment-based,the results of tested thermal stresses may have partially relaxed or combined the lattice mismattch strain and the thermal strain.Moreover,the laboratory test method can only get the stress value of some specific locations,resulting in that we can't have an intuitive understanding of the stress distribution of the entire GaAs layer.This thesis studies the thermal stress distribution of GaAs on nano-patterned Si,focusing the effect of a patterbed substrate on the reduction of thermal stress and the optimization of structural parameters.The main work and achievements of the dissertation are as follows:1.Based on the previous research in our laboratory,explored the thermal stress distribution of GaAs film on Si.Based on the theory of material mechanics and its derivation,studied the thermal stress state,and recognized the generation mechanism,properties and characteristics of thermal stress in GaAs film on Si.2.Adopted COMSOL Multiphysics to establish the model of our research,set up the physical field and boundary conditions,completed the numerical simulation and data processing.Verified the accuracy of the numerical simulation compared with the theoretical calculation.3.Established the model of GaAs on Si with plate substrate,and analyzed the thermal stress distribution of the model.We found that the Si substrate is under compressive stress and the GaAs film is under tensile stress.And in GaAs film the stress tensor is larger where is closer to the interface of GaAs film and Si substrate.However,the stress level doesn't fluctuate widely in the entire GaAs film and the stress values differ slightly.4.Studied the characteristics of the thermal stress distribution in GaAs on Si with patterned substrate.From the numerical calculation we found that using patterned substrate can reduce the thermal stress of GaAs on Si.The thermal strsee is reduced by 83%compared with using plate substrate,but only limited to the patterned area.The thermal stress in other regions has no significant differences between the model with plate substrate and patterned substrate.In addition,optimized the structural parameters of patterned substrate for the purpose of reducing the thermal stress.It is found that the thicker the SiO2 mask's thickness,the narrower the GaAs window area and the wider the SiO2 mask is,the smaller the stress is.