Fine structure of AlN/AlGaN superlattice grown by pulsed atomic-layer epitaxy for dislocation filtering

We report the detailed structure analysis of our AlN/AlGaN superlattice (SL) grown by pulsed atomic-layer epitaxy (PALE) for dislocation filtering. Due to the nature of PALE, the AlGaN well material itself in the SL was found to be composed actually of an AlxGa1-xN/AlyGa1-yN short-period superlattice (SPSL), with the periodicity of 15.5 angstrom (approximate to 6 monolayer), determined consistently from high-resolution x-ray diffraction and high-resolution transmission electron microscopy measurements. The SPSL nature of the AlGaN layers is believed to benefit from the AlN/AlGaN SL's coherent growth, which is important in exerting compressive strain for the thick upper n-AlGaN film, which serves to eliminate cracks. Direct evidence is presented which indicates that this SL can dramatically reduce the screw-type threading dislocation density. (c) 2005 American Institute of Physics.