Research On Key Technologies Of Ge-based Light Emitting Devices

With the development of integrated circuits,the problems of power consumption,signal delay,and electromagnetic interference caused by conventional electrical interconnections become more and more prominent,which hinders further reduction in the size of integrated circuits.Using optical interconnects to replace electrical interconnects as information transmission channels on or between chips is a widely recognized solution to break the traditional electrical interconnect bottleneck.III-V materials have relatively mature light-emitting devices and good luminescence properties,but they are not compatible with Si-based CMOS processes thus not suitable for Si-based monolithic optoelectronic integration.The light-emitting device of the Group ? materials can be compatible with the Si process,becoming a development direction for achieving monolithic photoelectric integration.Although the Ge material is the indirect band gap material,its energy difference between the direct band gap and the indirect band gap is only 0.136 eV,which can realize direct band gap luminescence through strain,electron filling,etc.Based on the characteristics and band structure of Ge,a variety of methods for introducing the strain is summarized and analyzed.It is also found that the strain can not only reduce the direct band gap energy valley and increase the maximum point of the valence band,but also increase the electron concentration in the direct band gap energy valley and carrier's mobility,which lays the foundation for the design of Ge-based LEDs and lasers.Based on the principle of LED illumination,combined with the advantages of external strain source,micro-bridge structure,Sn-doped and PIN heterojunction structure,a novel strained Ge/Ge_1-xSn_x/Ge PIN double heterojunction light-emitting diode is designed.After integrating and optimizing the process steps,the performance of the device is analysised by changing the physical parameters of the material.The experimental results show that the luminescence properties of the LED increase with the increase of strain;the optimum n-type and p-type doping concentration is 5×10¹88 cm^-33 when the strain of Si₃N₄ film is-1.38 GPa and the composition of Sn is 4.5%;combined with srtain and Sn-doped can reduce the Sn composition for the conversion of Ge into the direct bandgap material.Based on the research of LED,combined with the principle of laser illumination and the analysis of various laser cavity structures,a Ge/GeSn/Ge double heterojunction PIN VCSEL was designed and analyzed by Silvaco software.This kind of laser combines the effects of Sn component and super-injected to achieve the luminescence.The simulation results show that the Ge/GeSn/Ge double heterojunction PIN VCSEL satisfies the requirement of particle number inversion;its spectral linewidth less than 1nm;its characteristics satisfy the characteristics of the diodes;the thickness of the intrinsic layer affects the level of over-injection;increacing doping concentration appropriately and reducing the temperature can also improve the luminescence characteristics;the luminescence intensity is optimal when the Sn composition is compatible with the cavity structure;the optimum I region thickness is different for different Sn components;the higher the Sn composition,the higher the luminescence intensity at the optimum I-zone thickness when the Sn compositions compatible with the DBR cavity structure.Considering the difficulty of Sn doping,the final choice is not the highest Sn composition?8%?but 6%.At this time,the thickness of each layer of the DBR structure of SiO2/Si is 0.233?m/0.143?m,the peak wavelength of the luminescence of the GeSn material is about 2?m,and the luminescence efficiency is significantly improved compared with the published experimental results.Considering the current common level of technology and cost,the idea of“two-pronged approach”is put forward,that is,while designing new high-performance light-emitting devices using new materials and new processes,it is also important todesign a more economical device structure which adapts to the current general state of the art.To this end,the new Si_xGe_y/Ge/Si_0.5Ge_0.5.5 LED was designed,and the process steps were proposed at the same time,and the layout was drawn.