以週期性氮化鎵奈米孔洞層形成分散式布拉格反射器內光散射行為的模擬研究

Abstract

利用週期性氮化鎵奈米多孔層結構來形成分散式布拉格反射器，因其多孔層與實心層之間的折射率對比可高於由不同材料交替實心層組成的分散式布拉格反射器，反射率可以提高。然而這種分散式布拉格反射器中的奈米孔結構會導致強烈的散射，進而影響其反射率高低和反射帶寬。在本研究中，我們使用週期性邊界條件的模擬方法，探討此類多孔層分散式布拉格反射器的散射行為。在本研究中，我們假設多孔層中具有管狀孔洞結構，以模擬實驗中觀察到的實際結構。此外，我們採用傳輸矩陣的理論方法，基於有效折射率模型來評估分散式布拉格反射器的性能。模擬結果與理論評估結果之間的差異顯示孔洞散射的效果。研究發現，當入射光的偏振方向垂直於孔管延伸方向時，特別是在分散式布拉格反射器反射帶的短波長側，散射現象較為強烈。

A periodic GaN nano-porous layer structure can be used as an effective distributed Bragg reflector (DBR) because of its large refractive-index contrast between a porous layer and a solid layer, when compared with a DBR consisting of the alternating solid layers of different materials. However, the nano-pore structure in such a DBR can lead to strong scattering, which can affect its reflectivity level and reflection bandwidth. In this research, we use the simulation scheme of periodic boundary condition for evaluating the scattering behaviors of such a porous-layer DBR. In the simulation study, we assume a pore tube structure in a porous layer, imitating the pipeline-like pore structure observed in experiment. Also, we use the theoretical method of transfer-matrix to evaluate the DBR performance based on the effective refractive index model. The differences of the results between the simulation and theoretical evaluation show the effects of pore scattering. It is found that the scattering is particularly strong when the incident polarization is perpendicular to the pore tube extension direction, particularly on the short-wavelength side of the DBR reflection band.