Helical-type surface defects in InGaN thin films epitaxially grown on GaN templates at reduced temperatures
The surface morphologies of InGaN films grown at 780 degreesC by metalorganic vapor phase epitaxy were determined using atomic force microscopy. A qualitative model was developed to explain the observed instabilities in the step morphology of these films, namely, the formation of hillocks and v-defects that give rise to surface roughening. V-defects, observed at a surface density greater than 2 X 10(8)/cm(2) are a result of interactions between moving surface steps, cores of screw-type dislocations, and two-dimensional islands of atoms that form on the terraces during growth at high surface undercooling. A delay in the formation of v-defects in InGaN to a nominal thickness of 10 nm was observed and associated with the ammonia partial pressure and the interactions between steps associated with hillock islands and cores of screw-type dislocations. Hillock formation was attributed to a transition in the thermodynamic mode of film growth, as three-dimensional islands nucleated on the cores of screw-type dislocations at a density of 2 X 10(8)/cm(2). Explanations for the foregoing observations are based on growth model theory previously developed by Burton, Cabrera and Frank and on changes in the surface kinetics with temperature, In composition, and gas phase composition. (C) 2003 Elsevier Science B.V. All rights reserved.