Room temperature (RT) pulsed operation of blue (420 nm) nitride based multi-quantum well (MQW) laser diodes grown on c-plane sapphire substrates with lifetimes exceeding 6 hours have been demonstrated. Threshold current densities as low as 12.7 kA/cm2 were observed for 10×1200 μm lasers with uncoated reactive ion etched (RIE) facets. The emission is strongly TE polarized and has a sharp transition in the far field pattern above threshold.

Heteroepitaxy of hexagonal symmetry materials is more complicated than in the more usual case of cubic systems. In the growth of layers on the (0001) surfaces, the misfit dislocations always exhibit a screw component that leads to rotation of the epilayer in a 3 dimensional growth mode. The size of the islands will depend on many factors among which the substrate surface treatment, prior to growth, may be a predominant one. In this work, a comparative study is carried out for samples grown on plasma treated samples, with and without additional substrate annealing prior to epitaxy. It is found that the defect density can be brought below 109 cm−2, which is better than one order of magnitude in comparison to the layers grown on sapphire substrates. On top of the annealed substrates, the island growth is not obvious. Whereas, misorientations as large as a few degrees can be measured inside the layers on top of non annealed substrates, justifying the occurrence of high densities of threading dislocations.

We present the results of Raman measurements performed on AlxGa1−xN layers grown by MBE and MOCVD. The films were deposited on (0001) c-sapphire substrates, and the aluminum content covered the whole composition range for x from 0 (GaN) to 1 (AlN). It is shown that the energies of both A1(TO) and A1(LO) phonon modes smoothly increase with increasing x, indicating a one-mode behavior. The E2 phonon mode, however, presents a different behavior. Its energy increases very slowly with aluminum content and, for x≈0.4, a new phonon mode shows up which is shifted to higher energies by 50 cm−1. This new line leads to the E2 AlN mode for increasing aluminum content. The linewidths and intensities of these modes strongly depend on composition. These results are compared with recent theoretical calculations. Finally, the Raman selection rules in the MBE and MOCVD samples are compared and conclusions about the quality of the layers are drawn.

GaN based homo- and heterotype LED's have been fabricated and characterized which emit in the blue and ultra-violet part of the spectral range. Complete epitaxial LED layer sequences with different recombination zones have been grown using MOVPE as well as MBE. Subsequent to the material growth, chemically-assisted ion-beam etching and contact metallization are utilized to achieve full LED devices. MBE-grown homotype LED's reveal a peak in the output light spectrum at a wavelength of 372 nm with a linewidth being as narrow as 12 nm. GaN/InGaN LED's grown by MOVPE show visible single peak emission with linewidths of 23 nm. The optical output power as measured in a calibrated Ulbricht sphere is in the 1 μW regime.

A quasi-thermodynamic model accounting for kinetics of molecular nitrogen evaporation is applied to simulate the growth of binary and ternary group-III nitrides using atomic group-III elements and molecular ammonia as the sources. The values of the molecular nitrogen evaporation coefficients from the surface of GaN and AlN necessary for the simulation are extracted from experiments on free evaporation of the crystals in vacuum, while for InN only estimates are available. The growth process of AlN and InN is studied by analyzing the composition of the desorbed vapor species that are thought to influence the native defect formation in group-III nitrides. Different channels of desorption from the surfaces of group-III nitrides (related either to group-III atoms or to their hydrides) are compared. Specific features of the growth processes under the metal-rich and N-rich conditions are analyzed. The developed approach is extended to study the growth of the ternary compounds GaInN and AlGaN. The growth rate of ternary compounds versus temperature shows a two-drop behavior corresponding to the rapid increase of the respective group-III atom desorption. The effect is accompanied by a corresponding stepwise change in the solid phase composition. Factors retarding the growth of ternary compounds — the miscibility gap related to internal strain accumulated in the solid phase due to the lattice mismatch of binary constituents, and the extra liquid phase formation during growth — are discussed with respect to GaInN.

A simple analysis is provided to determine the characteristics of an electron cyclotron resonance (ECR) plasma source for the generation of active nitrogen species in the molecular beam epitaxy of III-V nitrides. The effects of reactor geometry, pressure, power, and flow rate on the dissociation efficiency and ion flux are presented. Pulsing the input power is proposed to reduce the ion flux.