| Silicon-based photonic device is one of the most promising integration platforms for high density heterogeneous optoelectronic integration.However,it is very difficult to solve the problem of silicon-based photonics light source.Because of the indirect bandgap nature of Group-Ⅳ bulk materials,Si and Ge are difficult to be fabricated as efficient light emitters for Si photonics.By contrast,Ⅲ-Ⅴ compound semiconductors with direct bandgaps demonstrate robust optical properties and provide an efficient gain medium for a laser source.Therefore,the heterogeneous integration of Ⅲ-Ⅴsemiconductor materials on silicon is an important way to realize silicon-based light source.It can not only achieve high economic benefits but also satisfy the requirements of high bandwidth for data transmission.Due to the remarkable quantum effects of quantum dot heterostructures,Ⅲ-Ⅴ quantum dot lasers have been considered as potential candidates for realizing feasible Ⅲ-Ⅴ/Si lasers because of their unique performance,such as low threshold current,high output power,high characteristic temperature,and high reliability,which are much less sensitive to threading dislocations.In this work,the transition from silicon to GaAs was realized with Ge as the buffer layer through molecular beam epitaxy technology,and then the growth of silicon-based InAs quantum dot laser was completed.Replacing the thick buffer layer with a low-defect-density Ge thin layer is considered an effective solution to prevent thermal crack generation and reduce defect density without affecting device performance.This method only requires a thin transition layer.It not only simplifies the integration process but also shortens the growth time.Therefore,it is necessary to use a Ge buffer layer to realize an InAs/GaAs quantum dot laser structure of MBE grown on a Si substrate.In addition,the transition from Si to GaAs is achieved with Ge thin buffer layer without equipment conversion.It is convenient to operate and avoid additional contamination due to equipment conversion.Therefore,the all MBE growth has the advantages of low cost,low pollution,high efficiency and high performance.This paper studies the epitaxial growth of InAs quantum dot materials and the heterogeneous integration of InAs quantum dot materials on silicon substrate,and finally successfully fabricated silicon-based light source.The research results achieved are summarized as follows:1.The growth conditions of InAs quantum dots were optimized,including deposition thickness,growth temperature,different As pressures and the number of the active region layers.In the growth of quantum dots,the low deposition thickness leads to the low density of InAs quantum dots,while the high deposition thickness leads to the increase of defects.Both of them lead to the degradation of luminescence properties of InAs quantum dots.Low growth temperature affects the migration of In atoms on the surface,while high growth temperature causes damage to quantum dots.Therefore,both too low and too high growth temperatures affect the luminescence performance of quantum dots.If the As pressure is too low,the luminous effect of the quantum dot is suppressed.Multilayer quantum dot structure can obviously improve the total gain and luminescence performance.By synthesizing the results of various conditions,we obtained the most suitable growth conditions for InAs quantum dots:deposition thickness of 2.7ML,growth temperature of 620℃,80%As pressure and active region structure of 7 layers of InAs quantum dots.2.The MEE growth technology can effectively inhibit the interdiffusion of different atoms at the heteroepitaxial growth interface,and obtain a flat epitaxial interface.This technology provides a guarantee for the growth of GaAs epitaxial layers with low defects and high quality on Ge.Due to uneven heating distribution of 4-inch wafers,we optimized the structure of the sample stand.We adjusted the temperature difference between the heating wires in the inner and outer rings,so that the 4-inch wafer was heated more evenly.High quality Ge buffer layer was obtained on Si substrate by a two-step growth method combined with low temperature and high temperature.The defect density was controlled below 106cm-2,which laid the foundation for the growth of subsequent InAs quantum dots.The density and width of the surface steps can be reduced by using a substrate with 60 misorientation towards[110].APBs are confined near the interface between Ge and GaAs to promote the initial annihilation of APBs.After completing all growth optimizations,we grew the InAs quantum dot laser on a 4-inch Si substrate and measured the sample by PL mapping.The measurement results of PL mapping show that InAs quantum dot laser has good uniformity,which lays a foundation for the fabrication of devices.3.The process of Si-based InAs quantum dot laser includes cleaning,making ridge strip,preparing n-contact electrode,surface passivation,etching window,deposition electrode and substrate thinning.After the fabrication of the silicon laser,the laser was packaged and its performance was characterized and analyzed.Continuous wave operation mode lasing spectrum centered at around 1.31 μm at room temperature,the characteristic temperature is 30K-40K,and the red shift velocity affected by temperature is 0.5 nm/℃,which is similar to the reported results of silicon-based InAs QDs lasers.The maximum continuous wave operating temperature of our silicon-based laser is 80℃.The continues work threshold current density is 365 A/cm2 at 20℃,and the maximum output power can reach 64 mW,achieving a high level.4.In order to further improve the performance of quantum dot laser,the growth structure and growth mode of InAs quantum dot laser active region are explored.On the basis of GaAs-based InAs quantum dot laser,active region Be-doped quantum dot laser and InAs/GaAs short period superlattice quantum dot laser are fabricated respectively.We find that Be doping in the active region can effectively improve the performance of the laser.The threshold current density of the laser is 100 A/cm2,the output power is 183 mW,and the maximum operating temperature is 130℃.Be doping improves the temperature stability of InAs quantum dot laser.Under continuous wave operation mode,it is found that the InAs quantum dot lasers fabricated by InAs/GaAs digital superlattices growth have good performances,with threshold current of 24 mA,corresponding to the threshold current density of 75 A/cm2.And the highest operating temperature reaches 120℃.Compared with the traditional laser,the InAs quantum dot laser grown by InAs/GaAs short-period digital alloy superlattice has good performance in terms of threshold current density,output power and temperature stability,which indicates that high quality laser can also be obtained by the growth way.Using InAs/GaAs digital superlattice growth mode,the composition can be changed without changing the temperature of the source oven.Thus InAs quantum dot laser with different luminescence wavelength can be obtained through this growth mode.InAs/GaAs digital superlattice structure can be used to realize different average In content in grown structure,providing a new idea for the design and growth of the active region of quantum dots. |
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