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The mechanisms responsible for the transparency of Ni/Au and Ni/Au/ZnO on p-GaN has been investigated. It was found that the optical transmission of Ni/Au contacts is dominated by the film thickness and morphology. A change in film thickness, induced by thermal annealing, results in a more transparent contact material. In addition a ZnO film was used as an antireflection layer on top of a Ni/Au contact. The Ni/Au/ZnO film was found to have an increased light transmission of 15% compared with an annealed Ni/Au contact. The maximum optical transmission measured through the Ni/Au/ZnO contact was 90%.

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A III-nitride blue LED structure based on the system of two wells with charge asymmetric resonance tunnelling (CART), which allows enhancing the number of the electrons captured into the active region with the quantum well, was systematically studied. The barrier design uses the charge asymmetric resonance-tunnelling phenomenon, which allows making the barrier transparent for electrons and blocking for holes. The growth and post-growth processes were optimised to achieve an efficient CART LED. The output power of 4 mW at the operating current of 20 mA has been achieved, corresponding to the external efficiency of 6%. Results presented in this report include the optimisation of the quantum well growth parameters, bowing parameter for InGaN alloys grown on GaN, dry etching of III-nitride materials, Ohmic contacts to p-and n-type GaN, electrostatic discharge (ESD) problems related with the reliability of LEDs. The results presented include also modulation-technique LED characterisation to tune the maximum radiative-recombination efficiency in accordance with the common operating current density.