Al 1 − x In x N layers with an indium content between x=10.5% and x=24% were grown by metal-organic vapor-phase epitaxy and characterized concerning their optical, structural and morphological properties with regard to the realization of optoelectronic devices. The indium content and the strain of these layers were measured by high resolution x-ray diffraction. Ellipsometric measurements were used to determine the optical constants [refractive index n(λ) and extinction coefficient κ(λ)] in dependence of wavelength and indium content. The values determined for the electronic bandgaps are in good agreement with theoretical predictions and previous publications on this topic but are more focused on AlInN layers which are pseudomorphically grown on GaN. A bowing parameter of b=10.3±0.1 was determined for fully strained layers with an indium content between 13% and 24%. In order to investigate the suitability of these layers for use in distributed Bragg reflectors, the surface morphology is characterized with respect to the indium content. Furthermore, the influence of an annealing step which often is necessary during device growth, was studied. The influence of this annealing step on the roughness was analyzed by atomic force microscopy, while structural features are monitored by high resolution secondary electron microscopy images. Based on these results distributed Bragg reflectors for the green spectral region with up to 40 pairs and a peak reflectivity of 97% have been realized. Transmission electron microscopic analysis of the layer interfaces are in good agreement with the atomic force and secondary electron microscopy images of the single layer surfaces.

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Self-organized and highly ordered GaN nanorods were grown without catalyst on r-plane sapphire using a combination of molecular beam epitaxy and metal-organic vapor-phase epitaxy. AlN nucleation centers for the nanorods were prepared by nitridation of the sapphire in a metal-organic vapor-phase epitaxy reactor, while the nanorods were grown by molecular beam epitaxy. A coalesced two-dimensional GaN layer was observed between the nanorods. The nanorods are inclined by 62 degrees towards the [Formula: see text]-directions of the a-plane GaN layer. The high degree of ordering and the structural perfection were confirmed by micro-photoluminescence measurements.

Most commonly used for the self-assembling of InGaN quantum dots is a Stranski-Krastanov growth scheme. Often neglected is the influence of spinodal decomposition, although it is frequently discussed with quantum well growth. In this publication we will expose the influence of both mechanisms on the formation process of quantum dots. This paper gives an insight in the theoretical background of quantum dot formation and covers the growth by molecular beam epitaxy and metal organic vapor phase epitaxy. Stranski-Krastanov like growth has been verified by the surface evolution beyond the critical thickness as seen by atomic force microscopy on uncapped samples. The overgrowth of such samples led to dissolution of the quantum dots. Indium compositions within the miscibility gap below critical thickness yielded spinodal phase separation in meander like structures These structures are in agreement with the theory from Hilliard and Cahn. Based on spinodal decomposition overgrowth schemes have been developed which showed reliable quantum dot emission. Such layers have been implemented into device structures such as LEDs and laser structures.

We report on a systematic study concerning the realization of nitride-based distributed Bragg reflectors (DBRs) for optoelectronic applications in the near-UV to visible spectral range. Different material combinations are used in order to find an optimized trade-off concerning peak reflectivity, stop band width, and strain state of the Bragg mirrors. For the high refractive index material GaN is used in all cases, while for the low index material a layer of either AlGaN or AlInN, respectively, or a AlN/(In)GaN short-period superlattice (SL) is employed. The best peak reflectivity of 97% at a wavelength of 495 nm is achieved for a lattice matched Bragg reflector based on the GaN/AlInN material combination.Transmission electron microscopy image of a 30-fold distributed Bragg reflector consisting of AlInN (dark) and GaN (bright) layers.

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We report on the growth of pit‐free a‐plane GaN on (1$ \bar 1 $02) sapphire (r‐plane) substrates by metal organic vapor phase epitaxy (MOVPE) using a three step growth method without low temperature nucleation layer. X‐ray diffraction ω ‐scans of the symmetric GaN (11‐20) reflex revealed for 1.2 μm thick crack‐ and pit‐free GaN layers low FWHM of 885 arcsec and 2484 arcsec measured by inclination in c‐ and m‐direction, respectively. To analyze the evolution growth was stopped at different stages and the samples were measured with AFM, SEM, and XRD. Furthermore, we discuss the overgrowth of MOVPE GaN layer with molecular beam epitaxy (MBE). For smooth MOVPE templates with closed surfaces the morphology was reproduced, whereas for not coalesced thinner layers a different growth mode and a smoothening of the layers occurred. We will discuss SEM‐ and AFMdata in detail to examine this overgrowth procedure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)