InGaN/GaN multiple-quantum-well light-emitting diodes grown on Si(111) substrates with ZrB2(0001) buffer layers

Multiple-quantum-well light-emitting diode (LED) structures of InGaN/GaN were grown by metalorganic chemical vapor deposition on Si(111) substrates via ZrB2(0001) buffer layers and a GaN template comprising composite AlxGa1-xN (where x lies in the range from 0 to 1) transition layers to minimize cracking due to thermal expansion mismatch between Si and GaN. Photoluminescence and electroluminescence results from the LED structures compared favorably with similar measurements obtained on identical LED structures grown on sapphire substrates. However, in spite of all the precautions taken, cracking was still present in the LED structures. Scanning electron microscopy and transmission electron microscopy in plan-view and cross-section geometries were conducted on the LED structures to examine the presence and the influence of various defects such as microvoids, micropipes, and threading dislocations on the mechanism of cracking. Our results suggest that the crack network propagates from microvoids on the surface of the LED structure. The formation of microvoids appears to originate from imperfections in the epitaxial ZrB2(0001) buffer layer.