V-shaped defects in InGaN/GaN multiquantum wells

InGaN/GaN multiquantum well (MQW) structures have been grown on (0001) sapp hire substrate by metalorganic chemical vapor deposition. From cross-sectio nal transmission electron microscopy (TEM), a number of V-shaped defects ha s been observed on the surface which are associated with mixed or pure-edge screw dislocations, as well as with inversion domains. Atomic force micros copy (AFM) reveals that these are hexagonal pits with a width of about 70 n m. The mechanism of formation of these defects has been discussed in terms of stress induced by lattice mismatch and reduced In incorporation on the ( 10 (1) over bar 1) planes in comparison to the (0001) surface. A decrease i n In concentration and also in well thickness during growth has been found. No optical emission has been observed from these defects by cathodolumines cence (CL) studies. (C) 1999 Elsevier Science B.V. All rights reserved.