Research On Modification Methods And Technologies Of Ge-based Materials

As an indirect bandgap semiconductor,germanium can be transformed into direct bandgap semiconductor through some specific modified methods,stress and alloying effect.Direct bandgap modified Ge semiconductor with a high radiation recombination efficiency can be applied for optoelectronic devices,which can improve the luminous efficiency dramaticlly;besisdes,direct bandgap modified Ge semiconductor can also be used for high-speed semiconductor devices to enhance the circuit function,speed and other key performance because of high carrier mobility.Therefore,the direct bandgap modified Ge semiconductor has the advantages in realizing monolithic optoelectronic integration and become a research hotspot in material fields.This topic mainly targets at how to achieve direct bandgap modified Ge semiconductors,including theoretical and experimental work,the detailed work is as follows:Based on the theory of strain tensor and deformation potential,the physical model of Ge bandgap conversion is established,which reveals the law that Ge transitions from indirect bandgap semiconductors to direct one.The results show that the transformation can be achieved when the?001?biaxial tensile stress of Ge material is about 2.4GPa;In the Sn alloying scheme,Ge is changed to direct bandgap when Sn component in the relaxed Ge_1-xSn_x material is about 8%;By combination of stress and alloying,direct bandgap Ge can be achieved in low Sn composition and low stress intensity.The theoretical results reveal the laws that Ge transforms from indirect bandgap to direct bandgap semiconductor,which can provide important theoretical basis for realizing direct bandgap modified Ge.According to the principle of Ge bandgap conversion induced by biaxial tension,a method of direct bandgap Ge compatible with Si process is proposed—the Ge epitaxial layer on the Si substrate is etched around,and the biaxial tensile stress is introduced by selective growth of Si_1-x Ge_x.A finite element stress model is established by selecting the Si_1-xGe_x region in Ge epitaxial layer to implement this method.The result of finite element simulation indicates when Ge component in Si_1-xGe_x epitaxial layer is 0.3-0.5 with150-250nm wide Si_1-xGe_x epitaxial layer,and Ge with 20-40nm in width can be transformed into direct bandgap semiconductor in the depth of 0-6nm.The physical and geometrical parameters of the Si_1-xGe_x growth zone are obtained based on the theoretical results,which can provide important theoretical basis for the realization of subsequent related processes.On the basis of the principle of Ge bandgap conversion induced by alloying,the magnetron sputtering technology is used to prepare high Sn component Ge_1-xSn_x alloy on Si substrate.The depostions of direct bandgap modified Ge are carried out,andan optimized implementation plan is raised.The results indicate that the Ge_1-xSn_x alloy with the best quality when the Sn content is about 18.86%,the substrate temperature is fixed at 150°C,Sn target sputtering power is 8W,and post-annealing temperature is at 300°C,then the RMS is 20.4nm.At the same time,the Ge buffer layer for direct bandgap Ge_1-xSn_x alloy is prepared on Si substrate by RPCVD process.The results show that the Ge/Si buffer layer has high crystal quality and low dislocation density,which improve the quality of the post prepared Ge_1-xSn_x alloy.The preparation of direct bandgap Ge_1-xSn_x alloy and Ge buffer layer on Si substrate in this study,which can provide important technical reference for the realization of direct bandgap Ge semiconductor.