Research On 1.3μm Silicon-based Quantum Dot Microdisk Lasers

With the rapid development of chip industry,the requirement for integration is getting higher and higher,and the technology of electrical interconnection is getting closer to its bottleneck.With the decreasing size of devices,electronic devices have approached their physical limit,and the cost of research and development has also increased continuously.The speed of renewal and growth of international semiconductor technology has slowed down.Optical interconnection technology has the characteristics of fast transmission,wide bandwidth and strong anti-interference ability,which provides a new direction for the development of silicon-based integrated chips.Using optoelectronic devices instead of electronic devices and optical interconnection instead of electrical interconnection is expected to solve the bottleneck problem of on-chip electrical interconnection.The wavelength of 1.3 μm is a low loss window of the optical fiber,and at this wavelength,the total dispersion of the single mode optical fiber is zero.In this way,the 1.3 μm wavelength region becomes an ideal working window of optical fiber communication,and is also the main working band of practical optical fiber communication system.Silicon-based semiconductor technology has been very mature in the development of silicon-based electrical interconnection.It is considered to be the most promising technology in the field of silicon-based optical interconnection.The luminescence,conductivity and doping concentration of direct epitaxy silicon-based III-V semiconductor materials are adjustable,which facilitates the adjustment and optimization of various functions of devices.In addition,the direct epitaxy material growth makes semiconductor materials more suitable for silicon-based photoelectric integration and large-scale growth,which is conducive to mass production.Silicon-based III-V quantum dot microdisk lasers have many advantages,such as high quality factor,easy integration,low power consumption and low cost.They have great advantages as light sources for silicon-based integrated chips.So far,many important advances have been made in the research field of silicon-based microcavity lasers.However,these studies mainly focus on material structure,growth process and device fabrication,and lack of systematic theoretical research on the structure of silicon-based microcavity lasers.In this paper,the structure parameters affecting the performance of 1.3 μm InAs/InGaAs quantum dot microdisk lasers with waveguide structure are studied.Finite-difference fime domain(FDTD)method is used to simulate the effects of cavity diameter,the thickness of cladding layers,the etching depth and the waveguide width on the quality factor of microdisk lasers.On this basis,we propose two new output structures and study their performance separately.Finally,the threshold current of the microdisk laser with different output structures is obtained by theoretical calculation.Specific work and research results are as follows:(1)Research on influence of the diameter on the silicon-based microdisk cavity.For microdisk cavities with diameter ranging from 4 to 12 μm,the quality factor increases when the diameter of microdisk cavity increases from 4μm to 7μm.When the diameter of the microdisk cavity increases from 7 to 12μm,the quality factor decreases rapidly.When the diameter is 7 μm,the quality factor of the microdisk cavity reaches its maximum.The optimum solution for the diameter of the microdisk cavity is 7 μm.(2)Research on influence of the cladding layer thickness on the silicon-based microdisk cavity is studied.As TE modes in the active region can be coupled into the cladding layers and propagate along the z and-z directions,the two modes interfere with each other,resulting in strengthening or weakening,thereby reducing or increasing the vertical radiation loss through the cladding layers.Therefore,the quality factor of the microdisk cavity varies periodically with the increase of the cladding layer thickness.When the cladding thickness is 1.75μm,the quality factor of the microdisk cavity reaches the first maximum.Considering practicability and economy,we set the cladding layer thickness to 1.75μm.(3)Research on effect of the etching depth on the silicon-based microdisk cavity.The quality factor of the microdisk cavity increases with the increase of etching depth.When the etching depth is 4.53 μm,the quality factor reaches the maximum value.As we continue to increase the etching depth,the quality factor remains stable.This phenomenon indicates that when the etching interface is lower than the interface between the lower cladding layer and dislocation filter layers,the constraints of the cavity will remain stable.Therefore,the etching depth of the microdisk cavity is set to 4.53 μm.(4)Research on the influence of waveguide width on silicon-based microdisk laser.For the microdisk laser with waveguide directly connected to the microdisk cavity,the quality factor of the microdisk cavity decreases rapidly with the increase of the waveguide width.The reason for this phenomenon is that when waveguides are connected to the microdisk cavity,it is equivalent to introducing defects into the microdisk cavity.The whispering-gallery modes in the cavity are destroyed by defects,and the mode distribution changes significantly,resulting in a sudden decrease in the quality factor.Therefore,the optimal solution of waveguide width is 0.5 μm.(5)Two new output structures of silicon-based microdisk lasers are proposed.Based on the traditional bus output waveguide structure,we design single-ended bus waveguide and bus waveguide which waveguide overlaps with microdisk cavity respectively,and study the performance of these two output structures through simulation calculation.When the size of the microdisk cavity,the thickness of the cladding layers and the etching depth are the same,the quality factors of the lasers with these two structures are maximized when the waveguide width is 0.5,m.When the notch width is 3.5 μm and the waveguide width is 1.5 μm,the modes in the waveguide tend to leak upward,which makes the structure suitable for the vertical coupled output structure.(6)It is theoretically proved that the designed microdisk laser can be lased.According to the rate equation and lasing conditions,the threshold currents of microdisk lasers with different output structures are calculated theoretically:for the lasers with output waveguide directly connected to the microdisk cavity,the threshold current is about 0.9 mA;for the lasers with waveguide and microdisk cavity overlapping,the threshold current is about 1.05 mA;for the microdisk lasers with single output waveguide structure,the threshold current is about 1.2 mA.Compared with other silicon-based microcavity lasers,the value of the threshold current calculated by our simulation is close to the experimental results,which proves that our designed microdisk lasers can achieve lasing in theory.