Study Of Energy Band Structure Of Direct Bandgap Ge_1-xSn_x

With continuous development of optical communication technology,the miniaturization and low power consumption of photoelectric signal conversion equipment becomes more and more urgent.Si-based monolithic optoelectronic integration circuits（MOEIC）in the same layer is an important solution of computing and communications for high performance,low-power MOEIC in the future.In the field of optical devices,electrical devices,and optoelectronics integration,III-V semiconductor materials have been widely used,but their incompatibility with the existing Si processes,high production costs,and long process cycles restrict their further development.Therefore,the search for new materials that are compatible with the current Si process and good photoelectric performance has become a new hot spot in the semiconductor field.Germanium（Ge）and silicon（Si）belong to the same Group IV semiconductor and they are compatible with the Si process.At the same time,Ge can be converted from indirect bandgap to direct bandgap semiconductor by common modification methods:?Alloying is used to form a direct bandgap relaxed Ge_1-xSn_x alloy(DR-Ge_1-xSn_x)when the Sn composition is x>8%;?Low-intensity tensile strain is used to form a quasi-direct bandgap Ge semiconductor（PD-Ge）;?The direct bandgap biaxial tensile strain Ge_1-xSn_x alloy(DBTS-Ge_1-xSn_x)is formed by the joint action of tensile stress and alloy.Direct/quasi direct bandgap type modified Ge(including DR-Ge_1-xSn_x,DBTS-Ge_1-xSn_x,and PD-Ge)has higher recombination efficiency than Ge carrier radiation and is applied to light emitting devices（LEDs,lasers）.The luminous efficiency of the device is significantly increased.Because of its energy-level splitting and effective mass reduction,the modified Ge has a higher carrier mobility than Ge,and it can also be applied to electronic devices.In a comprehensive view,the direct/quasi-direct bandgap type modified Ge material can realize the integration of a light emitting device,a waveguide,and a detector device in the same layer,and has great application potential in the field of MOEIC in the same layer.The band structure is the core theoretical basis for the development of the same-level MOEIC,and the in-depth study of the fundamental characteristics of semiconductor materials.At present,there are relatively few reports about the band structure of DR-Ge_1-xSn_x and DBTS-Ge_1-x-x Sn_x（PD-Ge band structure reported more）.Therefore,based on Schr?dinger equation and the deformation potential induced by strain,an 8-band kp method is applied to study the relationship between DR-Ge_1-xSn_x and the energy band,arbitrary wave vector at pointΓof the band edges and subbands are obtained from the conduction band energy band structure of DBTS-Ge_1-xSn_x,the electron,hole effective mass,density of states effective mass and other physical parameters.The results show that the hole effective mass of DR-Ge_1-xSn_x is anisotropic and the electron effective mass is isotropic.The energy level structures of the same crystallographic family in different directions are the same.The strain induced energy level atГpoint shifts,the degeneracy of DBTS-Ge_1-xSn_x band edge and the subband edge atГpoint is eliminated.The anisotropy of hole and electron effective mass increases significantly.Direct/quasi-direct bandgap modified Ge material realizes MOEIC on Si substrate,The forbidden band width relationship of the active layer materials of each device must satisfy:E_g,Waveguide>E_g,LED>E_g,detector.Considering the level of the integrated circuit technology at home and abroad,the two materials,DR-Ge_1-xSn_x and PD-Ge,are the most promising materials for Si-based MOEIC.It has become an important material at home and abroad.DR-Ge_1-xSn_x or PD-Ge to achieve the same layer MOEIC,both need to be able to modulate the energy band structure.Based on the theory of solid energy band,combined with strain tensor model and deformation potential model,the uniaxial stress-induced bandgap model of DR-Ge_1-xSn_x and PD-Ge is established,and the quantification results of the variation of the bandgap width under uniaxial stress are obtained.The results show that for DR-Ge_1-xSn_x and PD-Ge,the 0°uniaxial stress can be used to achieve widening or narrowing the forbidden band width,which can be applied to the bandgap modulation of waveguides or detectors,but the 45°tension/compression strain only can reduce the forbidden band width,so it only applies to the bandgap modulation of detectors.In this paper,the research of energy band structure,the physical parameters,and the quantification results of bandgap modulation of direct/quasi-direct bandgap modified Ge materials can provide important theoretical basis for the research of the active layer LED and the realization of MOEIC in the same layer in the Si-based optical interconnection.