Surface Morphology Evolution of AlGaN Microhoneycomb Structures during Epitaxial Overgrowth

The surface morphological development during epitaxial overgrowth of AlGaN on microhoneycomb (μ-HC) patterned relaxed AlGaN/AlN/sapphire templates is studied. Optimization of μ-pattern design and influence of various growth parameters are carried out in search for conditions resulting in coalescence of μ-HC structures into planar layers or ordered arrays of V-pits with well-defined crystallographic facets. It is found that in a wide range of growth conditions, formation of V-pits with semipolar facets occurs where their crystallographic orientation is defined by the geometry of the initial μ-HC patterns and growth conditions. High-temperature and high V/III ratio conditions are found to favor c-plane expansion and allow recovery of planarity on the patterned templates. Systematic study of surface morphology evolution in conditions favoring 1) semipolar facets formation and 2) coalescence is carried out and possible mechanisms underpinning the observed behaviors have been proposed.