Threading dislocation propagation in AlGaN/GaN based HEMT structures grown on Si (111) by plasma assisted molecular beam epitaxy

A transmission electron microscopy (TEM) study was carried out on a series of AlGaN/GaN high-electron mobility transistor (HEMT) structures grown by plasma assisted molecular beam epitaxy (PA-MBE) on Si (111). Threading dislocation (TD) behavior and density were investigated for three heterostructures using an AlN/GaN superlattice and/or differently strained GaN layers. Threading dislocation densities (TDDs) were measured by TEM (at different depths) and high resolution x-ray diffraction (HRXRD) allowing one of the most complete and few studies so far, presenting separated values on edge, screw and mixed type TDs quantities.