Research On Quantum Well Lasers Based On SiGeSn

As the size of semiconductor divices continuously reducing,the most important problem which limits the development of today's silicon integrated circuits is the electrical interconnection.In order to increase the interconnect density in integrated circuits while reduing the energy and latency consumed by interconnections,optical interconnects between chips and on-chip are proposed and explored by a large number of researchers.The biggest challenge in optical interconnection is the that the integrated optical devices are compatible with the traditional CMOS process.In the optical interconnection systems,the system components such as optical modulator,photodetector,waveguide have been fabricated using silicon or germanium and are compatible with silicon process.The main problem we are facing with is the lack of a silicon optical source which is compatible with the traditional silicon process.Because the silicon material itself is an indirect bandgap semiconductor,and has a very low luminous efficiency.Howerer,germanium has a slight energy difference which is just 136meV between the lowest energy point of?valley and L valley.Through doping,tensile strain or Si-Ge-Sn system alloy,we can obtain a direct bandgap semiconductor.This makes many research groups focus on changing the band structure of germanium material.In this paper,we focus on the GeSn and SiGeSn alloys in Si-Ge-Sn system.The SiGeSn-based lasers are designed by analyzing the change of the band structure of GeSn and SiGeSn alloys,which provides a possible solution for the design of silicon-based lasers.Firstly,because the SiGeSn alloy has a series of advantages,such as an adjustable band gap in the case of a fixed lattice constant,having direct bandgap and indirect bandgap.Then we proposed a silicon-based Si_0.15Ge_0.621Sn_0.229/Si_0.637Ge_0.018Sn_0.345 MQW laser in which the active region has 20 Si_0.15Ge_0.621Sn_0.229 quantum wells separated by 20Si_0.637Ge_0.018Sn_0.345 barriers.The maximal optical gain reaches 2300/cm with an estimated carrier concentration of 5×10¹⁸/cm³ which is equivalent to the transparent current density of 0.5kA/cm².Furthermore,the optical confinement factor and modal gain are discussed.The modal gain is sensitively depended on the number of the QWs which restricts the optical confinement factor.The modal gain of the model we proposed can reach 1500/cm with the injected current density of 3kA/cm².The results indicate that it is possible to obtain a Si-based near-infrared laser using SiGeSn al oy.In addition,GeSn can be converted to a direct bandgap semiconductor with the increasing of Sn component.SiGeSn alloy has a larger bandgap than GeSn.Based on the analysis of the band alignment of GeSn/SiGeSn quantum well structure and the selection principle of the well and barrier material in quantum well,the Ge_0.9Sn_0.1/Ge_0.71Si_0.14Sn_0.15 MQW laser was designed.The stress was eliminated by growing a Ge_0.71Si_0.14Sn_0.15 buffer layer between the substrate and the n-type Si_0.71Ge_0.14Sn_0.15 layer.A ridge waveguide was used to reduce the threshold current and increase the injection efficiency.The laser was simulated by Silvaco TC AD software.The results indicated that the energy band alignment in quantum well is consistent with the theoretical analysis.The lasing wavelength is 2.4?m,the threshold current of the model is 160mA,the TE mode gain reaches 6600/cm,and the mode gain reaches 110/cm.The simulation also showed the changes of the threshold voltage under different doping concentration and the changes of the mode gain under different number of quantum wells.The results indicate that the laser we design meets the design requirements of silicon-based lasers and provide a new solution for the research and development of the mid-infraed lasers and Si-based lasers.