Publication
Gallium Nitride (GaN) and its ternary alloys with aluminium and indium have met a growing interest in the last decade. These semiconductors have a large direct bandgap and can be doped with either silicon (Si) for n-type and magnesium (Mg) for p-type layers. Consequently, they are attractive targets for the fabrication of electrically driven light-emitting diodes, laser diodes and photodetectors, operating in the UV and visible range. Nitride semiconductors are also robust ans stable at high temperatures, suggesting their use in high frequency – high power electronic devices. The research on the III-nitride semiconductors is still in its infancy and, although several devices have been demonstrated and commercialized, there are still many issues to be solved. In particular, the III-nitride materials suffer from the lack of an adequate lattice-matched substrate for epitaxial growth, the high density of defects and dislocations, the poor quality of the p-type layers (low hole concentration and mobility), localization effects in indium containing layers, chemical inertness, etc… Also, due to the material quality issues, some electrical and optical parameters are only approximatively known. AlInN alloys have not attracted much attention compared to the InGaN and AlGaN ternary alloys, due to their unstable growth conditions. High-quality AlInN layers were deposited by metalorganic vapor-phase epitaxy (MOVPE). AlInN with an indium content of 18% is lattice-matched to GaN. It has a bandgap energy of about 4.35 eV and a refractive index contrast to GaN of 7% at 450 nm. It is shown that the optical, electrical and structural characteristic of epitaxial AlInN layers start degrading above a critical thickness of 200 nm, due to an ongoing pollution of the MOVPE reactor by products of the reaction. The distributed Bragg reflector (DBR) is an essential building block for advanced optoelectronic devices such as vertical-cavity surface emitting lasers (VCSELs). The introduction of the lattice-matched AlInN quarter-layers allows to grow thick DBR structures, with limited strain issues. It is used with GaN quarter-layers for visible reflectors and AlGaN quarter-layers for UV reflectors Optimizing the growth conditions of AlInN layers leads to the realization of DBRs with reflectivity above 99 % in the blue wavelength range (410-450 nm) as well as in the UV wavelength range (345 nm). The novel AlInN/GaN DBR is introduced in various microcavity LED (MCLED) structures. The basic features of the MCLED devices are presented, as well as optical simulations obtained using the transfer matrix representation (TMR) formalism, coupled with a dipole approximation for source terms. Electrical characterizations on these devices show that an intra-cavity contact (ICC) scheme should be used to achieve a sufficient electron injection in the active region. The external quantum efficiency of MCLED devices with thick AlInN/GaN DBRs (12 pairs) were lower than expected, due to the degra