Loss characteristics analysis and process optimization of gallium nitride optical waveguide
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摘要:
本文利用基于光束传播方法(Beam Propagation Method，BPM)的有限元仿真模型研究了氮化镓(GaN)平面光波导的传输损耗特性，针对传统GaN波导损耗较大的问题提出了工艺优化方案。通过构建完整的传输损耗模型，系统分析了波导几何参数对传输特性的影响，重点研究了顶部刻蚀和背后减薄两种优化工艺的改善效果。研究表明，这两种工艺均可显著降低波导传输损耗：顶部刻蚀工艺可将损耗从2.29 dB/mm降至0.19 dB/mm，背后减薄工艺可降至0.24 dB/mm。此外，本文还量化分析了制造工艺引入的侧壁夹角和表面粗糙度等缺陷对传输损耗的影响，并通过参数优化确定了实现可见光单模传输的关键结构尺寸。研究成果为设计和制备低损耗GaN平面光波导提供了理论依据和工艺指导。
Abstract:This study investigates the transmission loss characteristics of gallium nitride (GaN) planar optical waveguides using a finite element simulation model based on the Beam Propagation Method (BPM). To address the high transmission loss in conventional GaN waveguides, we propose process optimization solutions and develop a comprehensive transmission loss model for systematic analysis. Our investigation focuses on comparing the effects of top etching and back thinning processes on waveguide optimization. Both processes significantly reduce the waveguide transmission loss, with the top etching process reducing loss from 2.29 dB/mm to 0.19 dB/mm and the back thinning process reducing it to 0.24 dB/mm. Additionally, we analyze the impact of manufacturing defects, such as sidewall angles and surface roughness, on transmission loss. Through parameter optimization, we identify the key dimensions necessary for single mode light transmission. This study provides a theoretical basis and process guidance for the development of low-loss GaN waveguides.
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图 8 氮化镓波导的光场传输模式分析(波导横截面)(a) 初始模型，(b) 顶部刻蚀工艺去除平板层，(c) 背后减薄工艺去除平板层，(d) 波导宽度150 nm高度100 nm实现单模传输，(e) 波导宽度100 nm高度150 nm实现单模传输
Figure 8. Analysis of light field transmission mode of GaN waveguide (waveguide cross section) (a) initial model, (b) top etching process removes the flat layer, (c) back thinning process removes the flat layer, (d) single-mode transmission achieved by waveguide width 150 nm and height 100 nm, (e) single-mode transmission with waveguide width 100 nm and height 150 nm
图 1 (a) 顶部刻蚀GaN平面光波导的加工流程图，(b) 背后减薄GaN平面光波导的加工流程图，(c) 两种GaN平面光波导的横截面示意图
Figure 1. (a) the processing flow chart of the etched GaN planar optical waveguide at the top, (b) the processing flow chart of the thinned GaN planar optical waveguide at the back, and (c) the cross-sectional diagram of the two types of GaN planar optical waveguide
图 2 初始模型下GaN平面光波导的折射率分布图
Figure 2. Refractive index distribution of GaN planar optical waveguides under the initial model
图 3 GaN平面光波导的相对光功率分布(波导传输方向)(a) 初始模型，(b) 顶部刻蚀工艺去除脊型波导下方平板层，(c) 背后减薄工艺去除脊型波导下方平板层
Figure 3. Relative light output distribution of GaN planar optical waveguide (waveguide transmission direction) (a) initial model, (b) top etching process removes the lower flat layer of ridge waveguide, and (c) back thinning process removes the lower flat layer of ridge waveguide
图 4 两种不同工艺下随平板层厚度变化的氮化镓波导传输损耗
Figure 4. GaN waveguide transmission loss with plate thickness under two different processes
图 5 两种不同工艺下随侧壁夹角变化的氮化镓波导传输损耗
Figure 5. GaN waveguide transmission loss as a function of sidewall angle for two different processes
图 6 两种不同工艺下随粗糙度变化的氮化镓波导传输损耗
Figure 6. Transmission loss of GaN waveguide as a function of roughness for two different processes
图 7 两种不同工艺下随波导宽度变化的氮化镓波导传输损耗
Figure 7. GaN waveguide transmission loss as a function of waveguide width for two different processes
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