2009 Volume 50 Issue 5 Pages 1085-1090
In order to examine the effect of threading dislocations on the structure of InGaN/GaN multiple quantum wells (MQWs) grown by metal-organic vapor-phase epitaxy (MOVPE), epitaxial lateral overgrowth (ELO) on a patterned sapphire substrate was employed and the MQWs were characterized as a function of the lateral position in terms of cathode luminescence (CL), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The intensity of a blue luminescence peak (426 nm) was larger for the epitaxial layer overriding on the masks than that for the layer on the unmasked area, while the peak wavelength was independent of the position. Threading dislocations, which were generated at the GaN/sapphire interface, did not propagate to the surface of GaN layer on the masks. The thicknesses of both the InGaN well and the GaN barrier, on the other hand, were the same for the MQWs both on the unmasked surface and on the masks, which is consistent with the invariable peak wavelength of the blue luminescence. For an InGaN well with the indium content of around 10%, it seems that the existence of threading dislocations does not affect the structure of the MQWs but just reduces the luminescence intensity through a recombination via mid-gap states.
