Study On Tension Strain Ge Vertical Structure LED

Starting from the characteristics of strained Ge materials,the strained Ge LED device model was built by using the semiconductor device simulation software Silvaco TCAD and the results were analyzed.The Si-Ge-Si double heterojunction structure LED was fabricated experimentally.And the test outcome show that the research purposes is reached.The work of the thesis is composed of three aspects: the study of strained Ge material properties,the simulation analysis of LED device structure and the preparation process of LED devices.This work firstly studied the energy band structure,carrier distribution and refractive index of Ge materials.The calculation of energy band structure of Ge material by Van de Walle deformation potential theory shows Ge material can be transformed from indirect band gap to direct band gap under 1.75% tensile strain.According to the distribution law of electrons in Ge materials,the dependence of electron concentration on doping concentration,temperature and stress is calculated.The calculation results show that increasing the doping concentration can increase the quantity of carriers in the conduction band.But because the impurities cannot be completely ionized,when the doping concentration is too high,the amount of carriers in the ? energy valley is not significantly improved.It is impossible to effectively improve the luminescence intensity by this means.Increasing the temperature can ? the ionization rate of impurities,thereby increasing the luminescence intensity.Introducing tensile stress can significantly increase the amount of electrons in the ? valley,thus increasing the stress is a effective method to increase the luminescence intensity.In addition,the work also established a model between the stress magnitude and the refractive index.The test results of the ellipsometer are basically consistent with the model.Further,according to the working principle of the LED device,the Ge-LED device model is built and studied by using semiconductor simulation software TCAD.Firstly,we compared the performance of Si-Ge-Si double heterojunction structure and pure-Ge structure devices.The simulation results show that when there is no strain in the active region,both structural devices can emit photons with energy of 0.8V(the corresponding emission wavelength is 1550nm).Due to the super-injection effect of heterojunction,under the same working condition,the amount of unbalanced carriers in the active region of Si-Ge-Si structure is much higher than the pure Ge structure,and the output optical power of the double heterojunction device is much larger than that of the pure Ge structure device.Therefore,it is more suitable to prepare an LED device by using a double heterojunction structure.Then,the effects of doping concentration,active region length,operating temperature and stress of active region on performance are investigated.The results show that the higher the doping concentration,the longer the active region,the higher the operating temperature,and the greater the active region stress can achieve the greater the output optical power.However,there are some problems in increasing the optical output power by the above method.Therefore,designing strained Ge LED requires overall consideration of performance,cost,and feasibility.Referring to the simulation results of the LED device,the process of Si-Ge-Si double heterojunction structure LED device was completed by RPCVD growth equipment.The process of LED device for tensile strained Ge materials is proposed.The strained Ge material sample had a good crystal quality,and the tensile strain was 0.24% with surface roughness less than 1 nm.By characterizing the electroluminescence spectrum of the LED device,the infrared luminescence peak around 1640 nm was successfully observed.With the increase of the injection current,the higher electroluminescence intensity was observed.The experimental results were consistent with the simulation results.