Self-Assembly Nanopillar/Superlattice Hierarchical Structure: Boosting AlGaN Crystalline Quality and Achieving...

As a burgeoning wide-band gap semiconductor material, Al_xGa_1-xN alloy has attracted great attention for versatile applications due to its superior properties. However, its poor crystalline quality has restricted the employment of AlGaN on electronic devices for a long time. Herein, we proposed a nanopillar/superlattice hierarchical structure for AlGaN epitaxy to boost the crystalline quality. The scale-controllable AlN nanopillar template is fabricated from a nickel self-assembly process. AlGaN initiates the epitaxial laterally overgrowth mode based on the nanopatterned template. In addition, the Al_xGa_1-xN/Al_yGa_1-yN superlattice structure could effectively block the propagation of threading dislocation segments. The kinetics of the dislocation and epitaxy process in the hierarchical structure is intuitively demonstrated and analyzed. Consequently, the dislocation density of AlGaN grown by this method is significantly reduced by more than 30 times compared to the AlN template. No threading dislocation segments were observed in the 4 μm TEM field of view. Moreover, based on the hierarchical structure, we also fabricated an AlGaN ultraviolet avalanche photodiode (APD). The APD exhibits superior performance, achieving a maximum gain of 1.3 × 10⁵ and high responsivity of 1.46 A/W at 324 nm. The reliability of the nanopillar/superlattice AlGaN epitaxial procedure is anticipated to shed new light on the nitride semiconductor material, further bringing a breakthrough to wide-band gap electronic devices.