Investigation On Surface Roughness Improvement And Dislocation Filter Layer Of Silicon-based GaAs

With the development and application of big data,cloud computing,and other communication technology,the amount of data generated by society shows a trend of rapid growth.The devices used in data centers for short-distance and large-capacity data transmission are still microelectronics.Due to the bottleneck in the development of microelectronics technology,it is difficult to control the transmission bandwidth,signal crosstalk,power consumption,and other indicators within a reasonable level in the face of such a large amount of exponential growth data.Silicon-based optoelectronic integrated circuit(OEIC)takes optical interconnection as the way of information transmission and the optical interconnection takes the advantages of high transmission rate,strong antiinterference,and low power consumption.Therefore,it has gradually become an important supplement to microelectronic technology and a key research direction for the development of information transmission devices.Currently wafer bonding technology and flip-chip bonding technology are mainly used in the commercialized silicon-based OEIC.However,flipchip bonding technology requires strict alignment conditions.The process of wafer bonding technology is complex and the maximum size is limited by the size of the III-V substrate,which makes it difficult to reduce the manufacturing cost.Technologies currently used are not conducive to large-scale production and application.In recent years,the direct epitaxial growth of III-V material on Si could be utilized for the benefit of large wafer sizes,lower costs,and the adopt of mature microelectronic processes has attracted extensive attention from researchers.The main problem with direct epitaxial growth is the dissimilarity between III-V materials and Si.This dissimilarity will lead to many defects in the materials during the direct epitaxy process,which seriously affect the crystal quality of epitaxial materials so that the performance and life of optoelectronic devices cannot meet the requirements of commercialization.The most detrimental and unsolved issue of direct epitaxial growth is the high density of threading dislocations.Various methods have been explored to reduce the threading dislocation density(TDD),such as threestep growth,patterned substrate,thermal cycling annealing,and the dislocation filter layers(DFLs).More recently,several groups have demonstrated successes in TDD reduction with the use of multiple strained layer superlattice(SLS)as DFLs.It is found that the average TDD decreased as the number of sets of DFL increased.However,the strain in the material will continue to accumulate with the increase of the sets of DFL.Excessive strain will cause material relaxation and affect the crystal quality.Therefore,the sets of the DFL are limited,which greatly affects the effect of dislocation filtering.Therefore,we optimize the existing DFL in this thesis.While it is found that the rough surface of GaAs/Si(001)will seriously affect the crystal quality of subsequent growth materials and device performance,even lead to the failure of the overall preparation process of devices.The poor surface morphology has become an urgent problem to be solved in the realization of silicon-based OEIC.Based on the above research background,this thesis focuses on improving the poor surface morphology and reducing the high TDD of GaAs/Si(001).The specific work and research results are as follows:(1)A strain-balanced superlattice structure and preparation scheme are proposed to effectively improve the surface morphology and crystal quality of GaAs/Si(001).From the comparison of characterization results,we can see that the root mean square roughness of GaAs/Si(001)samples with this scheme is reduced from 1.92nm(10μm×10μm)to 1.16nm(10μm×10μm).In terms of crystal quality,the average peak intensity was increased by 500.3%under room temperature photoluminescence.The average peak full width at half maximum(FWHM)decreased from 31.6nm to 23.4nm.The peak intensity of the X-ray diffraction curve increased from 2750 to 15736,with an increase of 472.2%.The peak FWHM decreased from 536arcsec to 373arcsec,which has a decrease of 30.4%.Combined with the epitaxial growth mode theory,we found that after the improvement of this scheme,the growth mode of GaAs/Si(001)material changed from the layer-by-layer growth in FM mode to the step flow mode,thus greatly improving the surface morphology of GaAs/Si(001).(2)A scheme of strain-balanced superlattice DFL which combines compressive strain layer and tensile strain layer is proposed.Two groups of samples were prepared by metal organic chemical vapor deposition(MOCVD).Group A used the InGaAs/GaAsP material strain balanced superlattice scheme,and group B used the InGaAs/GaInP material strain balanced superlattice scheme.The crystal quality of the samples with different schemes was characterized by atomic force microscope,photoluminescence,X-ray diffraction,and electron channel contrast imaging.According to the characterization results,the root mean square roughness of group A was 31.1%lower than that of group B.In terms of crystal quality,the peak intensity of room temperature photoluminescence of group A was 255.8%higher than that of group B.The peak intensity of X-ray diffraction of group A was 23.9%higher than that of group B.In terms of dislocation density,the dislocation density of group A is 6.3×108 cm-2,while the dislocation density of group B is 7.8×108cm-2.Therefore,InGaAs/GaAsP strain balanced superlattice scheme has a better improvement effect.