Investigation Of Strain Engineering For Mid-Infrared Detector And Light Emitter Based On GeSn Alloys

The bandgap of germanium-tin?GeSn?alloy can be tuned from 0 to 0.66 eV.As the Sn composition is larger than 6.7%,GeSn can be turned into a direct bandgap material.Theoretically,the cut-off wavelength of silicon?Si?-based photonic devices using GeSn alloy can be extended into mid-infrared,even far-infrared range.However,the maximum Sn composition of GeSn used in photonic devices is only around 13% due to the limited solubility of Sn in Ge,which makes the cut-off wavelength of GeSn photonic devices less than 3 ?m.Besides Sn composition,strain also plays an important role in modulating the band structure of GeSn.Applying tensile strain into GeSn contributes to the reduction of bandgap and the transition from indirect bandgap to direct bandgap.This thesis studied the strain engineering for GeSn mid-infrared photonic devices.The main contents and results are listed as follows:?1?According to classic elastic mechanics theory,the strain simulation model applied to GeSn photonic devices is built.Devices with different structures are designed.Tensile strain induced by silicon nitride?Si₃N₄?liner stressor is introduced in GeSn photonic devices and the strain distribution is studied.The results show that biaxial tensile strain within?100?-plane is introduced into GeSn fin photodetectors.The strain induced into GeSn waveguide and pillar photodetectors is tensile strain along the three principle coordinate directions.A large and uniform in-plane?001?biaxial tensile strain is induced in GeSn microdisk structure.?2?The band structure simulation model is built based on k?p perturbation theory.The impacts of strain and Sn composition on the band structure and the relevant properties of GeSn alloys are discussed.The different band structures are designed according to the different requirements of devices,and the device structures are optimized based on the simulation results of the band structure.Under the tensile strain,there are some improvements in the GeSn properties in the active region of photonic device.1)The Sn composition required for indirect to direct bandgap transition is reduced,which is attributed to the more rapid decline of the ? valley than that of the L valley.Compared with the relaxed GeSn alloys,the critical Sn composition for the transition in tensile strained GeSn waveguide photodetectors is reduced from 6.7% to 3.5%.What's more,the Sn composition of 2.5% is required for the transition in tensile strained GeSn/SiGeSn double-heterostructure light emitting diode.2)The direct bandgap EG,? is significantly reduced.The EG,? of tensile strained Ge0.90Sn0.10 in 100 nm fin,waveguide,and 100 nm pillar photodetectors are decreased to 0.31 eV,0.306 eV,and 0.285 eV,respectively.Compared to the relaxed Ge0.90Sn0.10,a reduction of 0.13 eV is achieved in the tensile strained Ge0.90Sn0.10 in the microdisk structure.3)The carrier effective masses are reduced and the ratio of the electron concentration ne,?/ne,total in the ? conduction valley is increased.Tensile strained GeSn double-heterostructure light emitting diode achieves more than 10 times higher ne,?/ne,total compared to the unstrained GeSn device.ne,?/ne,total in tensile strained Ge0.90Sn0.10 multiple-quantum-well microdisk laser with a ne,total of 1017 cm-3 reaches 65%.?3?Tensile strained photodetectors wrapped in Si₃N₄ liner stressor with different structures are designed.The impact of tensile strain on the detection range of the devices is investigated.With optimized dimension,the cut-off wavelengths of strained Ge0.90Sn0.10 fin,waveguide,and pillar photodetectors are extended to 4 ?m,4.06 ?m,and 4.35 ?m,respectively.With the external electric field,the photo-response range of tensile strained waveguide photonic devices can cover the whole 2 5 ?m mid-infrared range.?4?The tensile strained GeSn/SiGeSn double-heterostructure light emitting diode is designed utilizing strain engineering.The impact of tensile strain on the luminescence intensity,emission peak,and internal quantum efficiency is investigated.The important parameters,such as carrier injection density,doping concentration,and the crystal quality of active region,affecting the luminescence performance of light emitting diode,are comprehensively studied.?5?Tensile strained GeSn/SiGeSn double-heterostructure laser and multiple-quantum-well laser are designed by utilizing external stressor.The influence of tensile strain on the threshold current,emitted wavelength,and optical gain is studied.When optical loss is 150 cm-1,the threshold current density Jth values of tensile strained Ge0.90Sn0.10/Si0.161Ge0.695Sn0.144 double-heterostructure laser and multiple quantum well devices,are reduced from 296 to 156 A/cm2 and 346 to 95 A/cm2,respectively.?6?Solid source molecular beam epitaxy?MBE?equipment is employed to grow the single crystal GeSn with high quality and Sn composition up to 8% on Ge virtual substrate.The Si-based GeSn mid-infrared photodetector is realized experimentally.The working wavelength for fully strained Ge_0.92Sn_0.08 mid-infrared photodetector extends up to 2 ?m,which is consistent with the theoretical results of the cut-off wavelength of the material,2.04 ?m.