We have determined the structure of inverted hexagonal pyramid defects (IHPs) in multiple quantum wells InGaN/GaN by high-angle annular dark-field scanning transmission electron microscopy (HAADF STEM). HAADF STEM images reveal definitely that the IHP nucleates at a threading dislocation and grows in the form of a thin six-walled structure with InGaN/GaN {101̄1} layers. It has been found that IHPs start even at In-rich dots under adverse growth conditions.

We present an atomic-scale structural and compositional analysis of ultrathin layers in multiple quantum well InGaN/GaN, by high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM). A high-quality HAADF STEM image processed by two-dimensional smoothing and deconvolution provides precise atomic-column positions and clear contrast, thereby allowing us to map the strain field and In atom distribution in successive GaN and InGaN layers. We conclude from these maps that there is a local fluctuation of In atoms in the InGaN layers and the In-rich regions, considered as quantum dots, cause large expansion only along the [0001] direction.

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This study develops a highly transparent nickel-oxide (NiO )-indium-tin-oxide (ITO) transparent Ohmic contact with excellent current spreading for -GaN to increase the optical output power of nitride-based light-emitting diodes (LEDs). The NiO -ITO transparent Ohmic contact layer was prepared by electron beam in-situ evaporation without postdeposition annealing. Notably, the transmittance of the NiO -ITO exceeds 90% throughout the visible region of the spectrum and approaches 98% at 470 nm. Moreover, GaN LED chips with dimensions of 300 300 m fabricated with the NiO -ITO transparent Ohmic contact were developed and produced a low forward voltage of 3.4 V under a nominal forward current of 20 mA and a high optical output power of 6.6 mW. The experimental results indicate that NiO -ITO bilayer Ohmic contact with excellent current spreading and high transparency is suitable for fabricating high-brightness GaN-based light-emitting devices.