一种新型Si/SiGe/Si双异质结PIN电学调制结构的异质结能带分析

PIN结构是电光调制器中常见的一种电学调制结构, 该结构中载流子注入效率直接影响着电光调制器的性能. 在前期的研究中, 我们在SOI材料的基础上提出了一种新型Si/SiGe/Si双异质结PIN电学调制结构, 可以有效提高载流子注入效率, 降低调制功耗. 为了进一步研究这种新型调制器结构的调制机理, 本文从单异质结能带理论出发, 定量分析了该新型结构中双异质结的势垒高度变化, 给出了双异质结势垒高度的定量公式, 将新型结构与SiGe-OI和SOI两种PIN电学调制结构进行能带对比, 分析了该新型结构载流子注入增强的原因, 最后模拟了新型结构的能带分布, 以及能带和调制电压与注入载流子密度的关系, 并与SiGe-OI和SOI两种PIN电学调制结构进行对比发现, 1 V调制电压下, 新型结构的载流子密度达到了8× 10¹⁸cm^-3, 比SOI 结构的载流子密度高了800%, 比SiGe-OI结构的载流子密度高了340%, 进一步说明了该新型结构的优越性, 并且验证了理论分析的正确性.

Analysis of Si/SiGe/Si double heterojunction band of a novelstructure of PIN electronic modulation

PIN is a common structure of electrical modulation in electro-optic modulator, and the performance of the electro-optic modulator is directly affected by the carrier injection in PIN structure. In previous studies, we have invented a novel structure of PIN electronic modulation based on SOI material. In the new structure, the SiGe material is adopted in the waveguide zone, therefore the double heterojunction PIN structure is formed in the horizontal direction. The carrier injection efficiency can be enhanced in the novel structure, and the power consumption could be reduced. In order to further study the modulation mechanism of the novel structure, based on the single heterojunction band theory, the barrier heights of the double heterojunction are analyzed, and the quantitative formulas of the barrier heights of the double heterojunction are given. It is shown that the barrier heights of the double heterojunction are related to the doping concentration, the band gap of material, the temperature, and the Ge content. The bands are compared between the novel structure, SiGe-OI structure and SOI structure to analyze the reason why the carrier injection of the novel structure could be enhanced. In the same conditions, the barrier heights of Si/SiGe/Si double heterojunction are minimal values, and those of SiGe and Si materials are second minimal value and maximal value, respectively. When the PIN device is set at a forward biased voltage (P region is the anode, and N region is the cathode), the balance between the carrier diffusion and the carrier drift is broken, and the PIN device is in a non-equilibrium state. According to the quantitative formula of the barrier heights of the double heterojunction, the barrier heights of Si/SiGe/Si double heterojunction are lower than that of SiGe-OI material, and the barrier height of SiGe material is lower than that of SOI material. It is shown that the barrier heights of Si/SiGe/Si double heterojunction could be flatten at first, so its PIN structure has the higher carrier injection than those of SiGe-OI and SOI under the same conditions. Finally, the band distribution of the novel structure and the relationships between the band distribution, the modulation voltage and the carrier injection are simulated. The results show that when the modulation voltage is 1 V, the carrier density of the novel structure arrives at 8×10¹⁸ cm^-3, which is 800% higher than that of SOI structure, and 340% higher than that of SiGe-OI structure. The advantages of the novel structure are further indicated, and the correctness of the theoretical analysis is also verified.