| At present,in the field of silicon-based optoelectronic integration,an important research direction is,based on Si,integrating the optoelectronic devices represented byⅢ-V compounds on a Si substrate.Therefore,it has both the excellent photoelectronic performance ofⅢ-V devices and the cost advantage of mature Si technology.The GeSi alloy template is suitable for a buffer layer between the Si-based substrate and the Ga As-based optoelectronic device.The traditional method of preparing GeSi template is to first grow a compositionally graded GeSi buffer layer on silicon,and then grow the GeSi template.However,this method is costly.And as for the GeSi template with high Gecomposition,the required thickness of buffer layer is larger,which is not conducive to subsequent device integration,so it is necessary to find a new preparation method.In view of this problem,this paper proposes a new method:using electrochemical etching,a porous silicon layer with a certain thickness is prepared on the surface of the Si substrate,and the porous silicon layer has a nanosized sponge-like structure.Then,by use of gas source molecular beam epitaxy,Geis filled in the nanopores of the sponge-like porous silicon layer.The GeSi template is fabricated by the interdiffusion of Geand Si in porous silicon layer under the high temperature conditions during the deposition.Compared with the traditional method,this method does not need to prepare the conventional compositionally graded GeSi buffer layer,so the thickness is smaller and the cost is lower.What’s more,the Gecomposition can be adjusted according to the conditions of electrochemical etching and Gedeposition.In this paper,according to this method,the GeSi template with high Gecomposition is prepared.The main work is divided into the following aspects:(1)A complete electrochemical etching system was independently designed and fabricated.Using the electrochemical etching process on this system,the sponge-like porous silicon with the nanopores structure was successfully prepared in solution of HF and ethanol,with a 1:1 volume ratio.The single crystal silicon substrate was etched for20min.The current density was set to 5m A/cm~2.The morphology of the as-prepared porous silicon samples were characterized by SEM.The results showed that the thickness of the porous silicon layer was uniform,about 2um.The morphology of the nanopores of porous silicon was further observed using TEM.The results showed that the average diameter of the pores was about 10nm.(2)Using the gas source molecular beam epitaxy system modified by our laboratory,Gewas deposited on porous silicon substrates at the temperature of 500℃,and the GeSi template was successfully prepared.SEM/EDS tests were performed on the samples,and the results showed that Geuniformly filled the nanopores of the porous silicon.(3)The PL tests of the samples demonstrated that compared with porous silicon,the PL spectrum of the GeSi template showed an obvious photoluminescence quenching phenomenon,indicating that the nanosized pore space of porous silicon is fully filled with Ge.(4)Raman spectroscopy was used to test and analyze the GeSi template.The appearance of Si-Gepeak indicated that Geand Si atoms are intermixed and form GeSi alloy during the high-temperature deposition process,indicating that the GeSi template was successfully prepared.On the surface of the GeSi template,Gecomposition is about 78%and a tensile strain of 0.5%is present.Further analysis of the composition of the GeSi template using HRXRD showed that the Gecomposition of the entire GeSi layer was about 70%,indicating that the GeSi template with a high Gecomposition was successfully prepared. |
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