We have studied the optical signatures of the Mg acceptor in GaN, using samples that are doped with Mg during MOCVD growth. In order to reduce the defect density in the material and thus achieve narrow linewidths in optical spectra we have used thick HVPE grown GaN layers as templates in the MOCVD growth. The photoluminescence (PL) spectra show two acceptor-related bound exciton peaks at 3.466 eV and 3.455 eV respectively. In the lower photon energy range the 3.27 eV emission with its LO-phonon replicas is dominant, riding on a broad background emission peaking at about 3.1 eV. These results, together with previous data in the literature, indicate that there are two acceptors in Mg-doped GaN, one dominating the optical spectra (the 3.466 eV and the 3.27 eV emissions) and another related to the 3.455 eV and the 3.1 eV emissions. We suggest that the latter is related to the Mg acceptor, while the former is a H-related complex, not necessarily involving Mg.

The application of SiN interlayers in GaN-based structures for the annihilation of threading dislocations captivates by its simplicity and the possibility to use it. However, since the metalorganic vapor phase epitaxy (MOVPE) of the group-III nitrides happens in a hydrogen-containing atmosphere, the surface decomposes during the SiN deposition. This work addresses the impact of the SiN growth with respect to temperature and surface dose. In particular, a quantitative analysis of the surface coverage is presented and the successive overgrowth with GaN is discussed in view of threading dislocation density and island growth mode.

GaN samples of this study were chemically wet etched to gain easier access to the dislocation sturcture. The scanning electron microscopy and transmission electron microscopy investigations revealed four different types of etch pits. After brief etching, several dislocations with screw component showed large etch pits, which may be correlated with the core of the screw dislocation. By means of SiNx micromasking the dislocation density could be reduced by more than one order of magnitude. The reduction of threading dislocations in the SiNx region in GaN grown on 〈0001〉 sapphire is due to bending of the threading dislocations into the {0001} plane, such that they form dislocation loops if they meet dislocations with opposite Burgers vectors. Accordingly, the achievable reduction of the dislocation density is limited by the probability that these dislocations interact. Edge dislocations bend more easily on account of their low line tension. This results in a preferential bending and reduction of dislocations with edge character.

The processing of homoepitaxial grown GaN based laser diodes by means of chemical assisted ion beam etching (CAIBE) is discussed. These laser diodes, emitting in the blue/UV spectral region, have been processed as buried ridge wave guide structures. Both, the influence of process parameters during etching such as the angle of incidence of the ions and gas fluxes as well as the impact of the ridge depth on the device performance will be analysed. Steep and smooth sidewalls of the ridge have been achieved by optimising the process parameters and by etching the ridge through the active region, cw-lasing has been achieved.

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