Tian Ye, Feng Peng, Zhu Chenqi, Chen Xinchi, Xu Ce, Esendag Volkan, Martinez de Arriba Guillem, Wang Tao
Department of Electronic and Electrical Engineering, The University of Sheffield, Sheffield S1 3JD, UK.
Materials (Basel). 2022 May 14;15(10):3536. doi: 10.3390/ma15103536.
Heavy silicon-doping in GaN generally causes a rough surface and saturated conductivity, while heavily silicon-doped -AlGaN with ≤5% aluminum can maintain an atomically flat surface and exhibit enhanced conductivity. Given this major advantage, we propose using multiple pairs of heavily silicon-doped -AlGaN and undoped GaN instead of widely used multiple pairs of heavily silicon-doped -GaN and undoped GaN for the fabrication of a lattice-matched distributed Bragg reflector (DBR) by using an electrochemical (EC) etching technique, where the lattice mismatch between AlGaN and GaN can be safely ignored. By means of using the EC etching technique, the -layers can be converted into nanoporous (NP) layers whilst the undoped GaN remains intact, leading to a significantly high contrast in refractive index between NP-layer and undoped GaN and thus forming a DBR. Our work demonstrates that the NP-AlGaN/undoped GaN-based DBR exhibits a much smoother surface, enhanced reflectivity and a wider stopband than the NP-GaN/undoped GaN-based DBR. Furthermore, the NP-AlGaN/undoped GaN-based DBR sample with a large size (up to 1 mm in width) can be obtained, while a standard NP-GaN/undoped GaN-based DBR sample obtained is typically on a scale of a few 100 μm in width. Finally, a series of DBR structures with high performance, ranging from blue to dark yellow, was demonstrated by using multiple pairs of -AlGaN and undoped GaN.
氮化镓中的重硅掺杂通常会导致表面粗糙和电导率饱和，而铝含量≤5%的重硅掺杂-AlGaN可以保持原子级平整的表面并表现出增强的导电性。鉴于这一主要优势，我们建议使用多对重硅掺杂-AlGaN和未掺杂的氮化镓，而不是广泛使用的多对重硅掺杂-GaN和未掺杂的氮化镓，通过电化学（EC）蚀刻技术来制造晶格匹配的分布式布拉格反射器（DBR），其中AlGaN和GaN之间的晶格失配可以安全地忽略。通过使用EC蚀刻技术，-层可以转化为纳米多孔（NP）层，而未掺杂的氮化镓保持完整，导致NP层和未掺杂的氮化镓之间的折射率有显著的高对比度，从而形成一个DBR。我们的工作表明，基于NP-AlGaN/未掺杂GaN的DBR比基于NP-GaN/未掺杂GaN的DBR表现出更光滑的表面、增强的反射率和更宽的阻带。此外，可以获得大尺寸（宽度可达1毫米）的基于NP-AlGaN/未掺杂GaN的DBR样品，而获得的标准基于NP-GaN/未掺杂GaN的DBR样品通常宽度在几百微米的尺度上。最后，通过使用多对-AlGaN和未掺杂的氮化镓，展示了一系列从蓝色到深黄色的高性能DBR结构。
