Growth And Characterization Of Ge Thin Films With Gradually Changed Si_1-xGe_x Buffer Layers On Si Substrate

At present,germanium monocrystalline three-junction solar cells are the mainstream of space cells.But germanium is a typical alkene bulk metal,the thickness of germanium sheet obtained by current slicing technology is about 100-300?m,while the effective Ge thickness in laminated cells is only about 10 ?m.Using thin film technology,high quality germanium thin films grown on silicon substrate to replace germanium single crystal can save material greatly and reduce cost.However,the thermal expansion coefficient of silicon is 2.44×106/K,the thermal expansion coefficient of germanium is 6.12×106/K,the thermal expansion mismatch is as high as 60%.Silicon and germanium interface is easy to produce larger mismatch dislocation,occurred in the process of annealing silicon germanium film crack,even fall off phenomenon.So how to grow a good quality of germanium on silicon substrate film is always the challenge of membrane preparation.Using dual targets magnetron sputtering equipment,Ge thin film with gradually changed Si1-xGex Buffer layers were prepared on Si(100)substrate.We explored the magnetron sputtering dual-target power control parameters of the Si1-xGex component gradient buffer layer,deposited and grown the Si1-xGex gradient buffer layer of Ge component gradient on the Si(100)substrate to reduce the misalignment between Si/Ge to prepare high-quality germanium films.The Ge film was annealed with rapid thermal annealing(RTA)equipment and conventional thermal annealing equipment.Ge thin film was characterized using X-ray diffraction(XRD),Raman spectrometer,scanning electron microscope(SEM)and metalloscope.The effects of substrate temperature,annealing temperature and annealing time on Ge film crystal quality were studied.The main research results are summarized as follows:1.Si1-xGex buffer layer interface is clear,element gradient distribution is uniform.The results of AFM show that the surface roughness RMS of 3.6 ?m germanium thin films prepared on this buffer layer is only 2.67 nm,which is much better than that of non-buffered germanium thin films.2.The magnetron sputtering process,the higher temperature of the substrate,the higher the germanium film crystallization degree,it was found that the sputtering critical germanium film crystallization temperature is 375 C and analyzed crystallization mechanism of germanium thin films during sputtering process.3.In the process of rapid thermal annealing,the germanium film does not fall off.Under the condition of 800 ?,110 s annealing,with the substrate temperature rises,germanium films from Ge(220)preferred orientation for Ge(111)preferred orientation,conducive to the late battery diffusion process.In view of this phenomenon,the paper makes a theoretical analysis of the preferred orientation.4.1n the conventional thermal annealing process,when the annealing temperature is critical crystallization temperature,the optimal crystal quality of germanium film is obtained.The crystal quality was further improved and Ge(111)diffraction peak ratio was enhanced.100 h annealing temperature is 350 0C annealing conditions,germanium films Ge(111)crystal plane diffraction peak of more than 90%.Compared with rapid thermal annealing,conventional annealing treatment can be carried out at low temperature.The obtained germanium film has higher Ge(111)preferred orientation.