Gallium nitride (GaN) is a well-investigated material that is applied in many advanced power electronic and optoelectronic devices due to its wide bandgap. However, derivatives of its monolayer form, such as bilayer structures, have rarely been reported. We study herein the electronic and optical properties of GaN bilayer structures that are rotated in the plane at several optimized angles by using the density functional theory method. To maintain the structural stability and use a small cell size, the twisting angles of the GaN bilayer structures are optimized to be 27.8°, 38.2°, and 46.8° using the crystal matching theory. The band-structure analysis reveals that the bandgap is wider for the twisted structures compared with the nontwisted case. The simulation results provide the absorption coefficient, extinction coefficient, reflectivity, and refractive index at these angles. The spectra of all these optical properties match with the bandgap values. The simulated refractive index of the bilayer structures at all the twisting angles including 0° is smaller than that of bulk GaN, indicating a reduced scattering loss for optoelectronics applications. Considering the results of this analysis, the possible applications may include low-loss integrated electronic and optical devices and systems.

中文翻译：

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扭曲双层GaN结构的电子和光学性质的第一原理理论研究

氮化镓（GaN）是一种经过充分研究的材料，因其带隙宽而被应用于许多先进的电力电子和光电设备中。然而，很少报道其单层形式的衍生物，例如双层结构。我们在这里研究了使用密度泛函理论方法在平面中以几个优化角度旋转的GaN双层结构的电子和光学特性。为了保持结构稳定性并使用较小的单元尺寸，使用晶体匹配理论将GaN双层结构的扭曲角优化为27.8°，38.2°和46.8°。带结构分析表明，与非扭转情况相比，扭转结构的带隙更宽。仿真结果提供了吸收系数，消光系数，反射率，和这些角度的折射率。所有这些光学特性的光谱与带隙值匹配。在包括0°的所有扭曲角下，双层结构的模拟折射率都比体GaN的模拟折射率小，这表明光电子应用的散射损耗降低。考虑到该分析的结果，可能的应用可能包括低损耗的集成电子和光学设备和系统。