Nitride Semiconductor Superlattice Buffer for Dislocation and Stress Control

The buffer layer is segmented into multiple alternating layers of AlN and AlGaN with different thicknesses. The first AlN layer has thickness of 2-10 nm, the first AlGaN layer has thickness of 3-20 nm, the second AlN layer has thickness of 10-50 nm, and the second AlGaN layer has thickness of 20-100 nm. This segmentation creates multiple interfaces that act as dislocation barriers, preventing dislocation propagation from the substrate through the nitride semiconductor layer, thereby improving reliability and breakdown voltage

Different regions of the buffer layer are assigned different material compositions and thicknesses to perform specific local functions. The thinner first AlN and AlGaN layers are positioned closer to the substrate for initial dislocation filtering, while the thicker second AlN and AlGaN layers are positioned farther away for additional stress management and dislocation blocking. This local quality differentiation optimizes the buffer layer's ability to manage dislocations and stress at different depths

The buffer layer is divided into four distinct sub-layers (first AlN, first AlGaN, second AlN, second AlGaN) with progressively increasing thicknesses. This segmentation allows each sub-layer to accommodate and manage stress differently, with the thinner layers near the substrate handling initial stress accumulation and the thicker layers farther away providing additional stress relief, thereby reducing overall internal stress in the nitride semiconductor structure

The buffer layer uses a composite structure of alternating AlN and AlGaN materials with different lattice constants and mechanical properties. This composite material approach creates a graded buffer that gradually transitions from the substrate lattice to the nitride semiconductor layer lattice, reducing misfit dislocations and managing thermal and mechanical stress throughout the layer stack